This PDF file contains the front matter associated with SPIE Proceedings Volume 10834, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and Conference Committee listing.

Metrology and quality are two sides of the same coin and high quality standards are a must for the majority of manufacturers in all industrial branches. Above all, optical principles have some exceptional properties that make them indispensable for use in all aspects of quality control. To them belong in particular the non-contact and high speed interaction with the object under test, the largely free scalability of the dimension of the probing tool, the high resolution of the data, the diversity of information channels in the light field, and the flexible adaptability of the measuring standard – the wavelength of light. On the other hand the user is confronted with a number of serious challenges. Some of the biggest challenges that currently attract high attention in both the technical and life sciences, relate to exceeding the physical limits of resolution, to be ready for the exploration of exotic materials and to improve the precision of the measurement. Therefore optical measurement methods are subject to constant improvement. The characteristics that give rise to improve the performance of the systems are obviously dependent on the purpose of the measurement and the object under test. But there are also general features that can be used to assess the performance of a measurement system. To them belong especially the spatial and temporal resolution, the area related resolution, the precision, the trueness, robustness, the degree of automation, the process capability and the ability to work as close as possible to the process. After a short introduction in the history of optical metrology, we describe some important fields of application and the optical measurement principles used there. Based on this we make an attempt to create a list of general and application dependent features for the assessment of modern measurement systems and propose measures to improve their performance. Finally we illustrate this on example of a new nano positioning and measurement device and show selected measurement results.

Be it quantum or classical, optical field is intrinsically of stochastic nature, and is generally composed of predictable and unpredictable components. It seems to be a common belief that the deterministic component of the optical field serves as a useful signal while its random component acts as a disturbing noise. Such a common belief based on the simple “good and evil dualism” does not hold for optical speckle fields, which have much subtler characteristics. While speckles are already known to be useful in optical metrology, they are still considered as a nuisance in imaging. This talk will introduce a methodology and techniques that illustrate how the speckles can be turned from a harmful noise to a useful vehicle for imaging.

Optical metrology provides very attractive means for noninvasive and highly accurate evaluation of different features of various objects. Information is acquired and processed over whole sensor area using so-called full-field methods. In coherent light techniques the measurand is stored in the complex amplitude of the optical field. Due to physical limitations the recorded intensity distribution is generally captured in a form of a fringe pattern with information encoded in phase and/or amplitude modulation distributions, hence the importance of their demodulation techniques. In this contribution several recently developed adaptive techniques for information retrieval in automated fringe based full-field optical metrology will be presented. Adaptivity constitutes advantage enabling robustness and versatility – presented methods adapt their performance according to characteristics of analyzed fringe patterns providing efficient means to successfully retrieve information obtained by various optical techniques, i.e., interferometry (classical two-beam, multi-beam, timeaveraged, speckle, grating), moiré and structured illumination. Developed fringe pattern demodulation techniques are based on the concept of single-frame processing using advanced image pre-filtering techniques, i.e., empirical mode decomposition and variational image decomposition. The phase/amplitude demodulation is conducted utilizing the 2D Hilbert transform and complex analytic signal paradigm. Applications of these specially tailored methods include but are not limited to: coherent phase microscopy for stationary and live biological objects (e.g., prostate cancer cells, red blood cells, semen cells etc.), vibration amplitude studies of technical microobjects, wavefront sensing, optical testing etc.

This communication presents a set of expressions to evaluate the standard uncertainty and covariance of the real an imaginary parts of the complex-valued field resulting from the reconstruction of digital holograms by using the Fresnel approximation. These expressions are derived by applying the law of propagation of uncertainty as defined in the “Guide to the expression of uncertainty in measurement” to the numerical evaluation of the Fresnel integral, understood as a linear function of the values in the digital hologram. The expressions are eventually applied to holograms produced by the interference of speckle patterns with uniform reference beams, and assuming that the square of the standard uncertainty in the digitized hologram depends linearly with its local values, according to the noise model adopted in the EMVA 1288 camera characterization standard. The resulting uncertainties and covariance of the real and imaginary parts of the reconstructed fields can be subsequently propagated to measurements of the phase change between holograms by following the procedure already presented in our previous work on the propagation of the measurement uncertainty in Fourier-transform digital holographic interferometry.

Digital simulations of speckle patterns are reported. Wavefront propagation and scattering by a diffusely reflecting surface is represented by a generalized Huygens principle for scalar light waves. The surface roughness is expressed by a set of random numbers that are uniformly distributed within variable range. No approximations for the propagation distances are employed between a point source and a surface point as well as between the surface point and an observation one. The 3-dimensionall intensity distributions in the diffraction field of the object that is illuminated by a spherical wave are calculated by adding many wavelets in complex amplitudes of the scattered waves at the observation point. The intensity distributions on the planes parallel and perpendicular to the object are calculated. For analyzing the speckle patterns illuminated by a multimode laser and multiple wavelength lasers incoherent superposition of the speckle patterns arising from superposition from various wavelengths or various source positions are calculated to investigate the effect of speckle suppression by addition of many speckle patterns.

This paper discusses on noise reduction in holographic data processing. Especially, for phase data in speckle metrology, related to a wrapped modulo 2π phase map, post processing is required to reduce random fluctuations such as the speckle phase decorrelation. The choice of the filtering algorithm is a challenge since a large variety of filtering schemes are available in literature. In addition, the metric for evaluating algorithms has to be discussed, especially regarding the need, or not, for a reference image. In order to assess the evaluations of the available de-noising strategies, we have constituted databases with simulated phase data. Then, 34 de-noising algorithms were chosen considering their efficiency in image processing and digital holography, as stationary wavelet transform based algorithm with Daubechies, symlets wavelet, curvelets, contourlets, BM3D (block matching 3D) algorithm (state of the art in the image processing), NL-means (non local) algorithms, 2D windowed Fourier transform and SPADEDH ; in addition, we consider classical methods such as Wiener, median and Gauss filtering, anisotropic filtering and Frost filter which was widely used in SAR (synthtic aperture radar) imaging. These schemes were evaluated through rankings provided by pertinent quality metrics. But, the main problem with quality metrics is that they are not self-sufficient in the sense that they require a noise-free reference phase fringe pattern in order to be computed. In practical situations, one only has a set of measurements to be processed, and no exact phase is available to evaluate the quality of processing. In order to bypass this limitation, a noise-free reference metric was developed, that means a metric which is directly capable of providing information on how efficient the filtering is, without the help of any reference measurement and by only considering the measured available phase data. So, we present and discuss on the rankings which were obtained, and in addition, we present a reference free metric adapted to phase data filtering in speckle metrology.

We are motivated by the question if scanning laser projection with low speckle noise is possible. Scanning laser projection requires “instantaneous” speckle reduction, within a few nanoseconds – meaning that no moving diffusors can be used. We will argue that instantaneous speckle reduction is possible by conversion of spatial coherence to spatial incoherence - but nature demands for a compensation. The cost can be estimated via the information theoretical concept “channel capacity”, which incorporates the etendue as well as the signal-to-noise ratio. We will show that an optical system with low spatial coherence (=low speckle noise) must provide significantly more degrees of freedom than a coherent imaging system. The consequence for the technical optical system is serious: significant speckle reduction can only be achieved by an excessively large projection aperture. This is not just a sophistic consideration, it seriously restricts the design of scanning laser projectors.

This paper presents the analysis of the influence of de-noising algorithms from the point of view of the contrast transfer function (CTF). The study focuses on amplitude images from digitally recorded holograms of the USAF target. In order to assess the evaluations, a database is constituted with experimental images extracted from 20 holograms acquired with a random illumination. Then, using the 20 amplitude images, 20 other images are computed in order to get images with increasing SNR (signal to noise ratio). In order to study the influence of de-noising algorithms on the CTF, 16 ROIs (region of interest) are selected in the USAF target. Each ROI corresponds to a specific pattern at a given spatial resolution. For the evaluations, 34 denoising algorithms were chosen considering their efficiency in image processing and digital holography. We choose advanced methods as stationary wavelet transform based algorithm with Daubechies and symlets wavelet, curvelets, contourlets, BM3D algorithm (state of the art in the image processing) and NL-means algorithms; in addition, we consider classical methods such as Wiener, median and Gauss filtering, anisotropic filtering and Frost filter which was widely used in SAR (synthetic aperture radar) imaging. From the ROIs, the CTF is evaluated. Then, we provide ranking of de-noising algorithms by considering the measured CTF. The variation of the CTF versus the input SNR is analysed for each algorithm.

Digital holography is practical technique for researching of 3D-objects parameters. There are various limitations of reconstructed image quality: speckle noise, twin image, zero order, shot noise, camera’s fixed pattern noise (FPN). In this work comparison of effect of digital camera’s main noise components on hologram reconstruction is investigated. Characteristics of different type’s cameras were used. It was obtained that for majority of cameras shot noise has higher effect on reconstructed images. However for various conditions FPN alone result in worse reconstruction quality than shot noise does. Borders of equal effect of shot noise and FPN on reconstructed images were obtained.

Metasurfaces, consisting of subwavelength nanostructures, have been considered a future holographic device that demonstrates unprecedented ability to control electromagnetic waves. In this invited talk, a general introduction to metasurface holography will be presented along with physical instruments and applications. In addition, complete complex-amplitude modulation holograms will be discussed in their theoretical and experimental demonstrations. Then we will discuss our vision of the future of this field including optical metasurfaces and meta-holograms.

The metamaterial filter introduced in the form of the so-called METATOY Johannes Courtial et al., j. opt. 13 (2011))[1] has a series of interesting properties, although it can presently only be realized as an array of discrete elements, being it an array of Dove prisms or lens arrays. Nevertheless, a theoretical analysis of field propagation through such a twisting filter is still lacking. Based on the complex-valued ray matrix formalism (ABCDmatrices/ canonical transforms), the propagation through such a filter can be mimicked by using the known Green’s function (e.g. Aykut et al. Journal of the Optical Society of America a (2010) 27(9) 1896)[2]. This matrix for an entire system including a flipping filter is non-symplectic, which in fact indicates that this filter’s perturbation is rayoptically forbidden. However, if we proceed and insert the matrix-values into this Green’s function, we arrive at results that are in agreement with the previously shown examples with METATOY. It is further shown how e.g. Fourier transformation of this filter will give rise to unexpected ray transformations. Finally, a new ray-optically forbidden element is discussed, as will possible future applications.

Speckle fringe patterns modulated by the third-order nonlinear optical behavior of Gold-Platinum nanoparticles in rotation were analyzed by a two-wave mixing configuration. Random interference patterns derived by speckles were obtained by employing a Nd:YAG laser system featuring nanosecond pulses at 532 nm wavelength for the measurements. The nanostructured samples were prepared by a sol-gel method and contained in a water suspension. Transmission electronic microscopy, UV-vis spectroscopy and Energy-dispersive X-ray spectroscopy studies were undertaken in order to characterize the samples. The bimetallic nature of the nanoparticles gave origin to an optically anisotropic response related to nonlinear optics enhanced by plasmonic excitations. The orientation of the samples produced important changes in the ratio between the real and imaginary parts of the third-order nonlinear optical susceptibility. Gyroscopic properties of the samples confirmed the possibility to identify mechanical motion of the system through the evaluation of induced birefringence and multi-photonic absorption. Vectorial self-diffraction signals generated by two-wave mixing experiments were explored to reveal the mechanisms responsible for the nonlinearities observed. The nanoparticles were incorporated in randomly distributed cells in order to monitor their mechanical activity by recording speckle fringe patterns. A self-focusing effect resulting from a positive nonlinear refractive index in the nanoparticles allowed us manipulating the location of the speckle fringe pattern; and then, a focusing system dependent on irradiation was proposed for the observation of mechano-optical processes. Nonlinear optical interactions for performing ultrafast all-optical instrumentation functions can be contemplated.

A complex amplitude imaging method based on a single-pixel camera architecture with a complex-amplitude representation is proposed. The use of the complex-amplitude representation of the input signal and the phase-shifting technique enables us to perform the phase imaging of an object, that is, profilometry. The complex-amplitude representation of the optical coding masks and a coherent addition that is performed by interference can directly represent the Hadamard patterns that have the positive and negative values. The complex-amplitude masks are displayed on phase modulation mode liquid crystal on silicon spatial light modulator (LCOS-SLM). Furthermore, the residual area of the mask is used for the reference beam with the phase shifting. Therefore, the complex amplitude imaging system with the coaxial structure has high stability for external disturbances.

Coherence induced noise and parasitic reflections in the experimental setup are main restrictions that limit the resolution and measurement accuracy in laser light-based digital holographic microscopy (DHM). We explored, if coherence properties of partial coherent light sources can be mimicked by utilizing spectrally tunable lasers. Moreover, the performance for label-free quantitative phase imaging of biological specimens is illustrated utilizing an experimental configuration including a commercial microscope and tunable super continuum laser sources with a wavelength range of up to 230 nm.

Crosslinked collagen hydrogel membranes are widely used in engineering tissue to promote the performance of biological processes involved in the healing of wounds, mainly in the presence of chronical diseases such as diabetes. One of the standard techniques used in biology to measure mechanical properties of hydrogels and tissues is based on a methodology called rheology. Rheological studies consist on the measurement of stress, strain and the ratio of stress to strain of several biological membranes to determine their viscoelastic properties. In this research work we propose as a proof of concept the use of digital holographic microscopy (DHM) and second harmonic generation (SHG) microscopy to compare qualitatively some basic image properties of collagen hydrogel membranes. Once demonstrated that this comparison is equivalent, we study under controlled excitation the biomechanical properties of collagen membranes by means of the analysis of the optical phase that results from comparing two consecutives holograms from a reference and deformed state. At this stage of characterization, an in depth study between rheological and holographic results will be performed in the near future.

In this paper, we review our recent work on the statistical properties of polarization speckle generated by a birefringent material with rough surface. After a short introduction of a less-known concept of polarization speckle with its unique properties of random polarization states fluctuating in space, we provide an intuitive explanation of the cause of polarization speckle by vector random walks in the complex plane for two components of the vectorial electric fields. The surface polarization scattering is investigated in terms of the coherence matrix, and a relationship between the statistical properties of the scattered light at the scattering surface and the micro-structure of the anisotropic media has been explored to understand the underlying mechanism. The coherence and polarization properties of the stochastic electric fields at the far field after propagation have been studied in order to describe their spatial structure and evolution. Furthermore, the dynamic properties of polarization speckle have also been investigated in order to investigate the simultaneous reduction of coherence and polarization of the scattered light for the first time.

Many optical applications requires often totally polarized light. However there are an other applications, such as optical spectrum analyzer, in which incident polarized light is undesirable. Insertion of depolarizer in such devices may stabilize the optical signal of the measured light, in order to reduce offsets in measurements. Liquid crystal are functional materials possessing anisotropies originating from their inner molecular alignment. A vertically aligned nematic liquid crystal with zero pretilts in the off state is isotropic for light impinging at normal incidence. However, the liquid crystal orientation upon electric switching is undefined; therefore the cell usually generates disordered birefringent medium related to undefined switching direction of molecules which produce random polarization of the transmitted light by liquid crystal cell, therefore depolarization effect is produced. In this work, the treatment of problems involving depolarization of incident polarized light beam passing through a depolarizing medium and general physical phenomena associated with it, will be investigated at the speckle scale. A suitable tool for this treatment will be real time Young’s interferometer constructed with a new principle including the possibility to control the fringe pattern in real time with objective to study the dynamics of speckle fluctuation. Modulation of depolarization control with an applied voltage are reported, also.

The early diagnosis of cancer is essential since it can be treated more effectively when detected earlier. Visual inspection followed by histological examination is, still today, the gold standard for clinicians. However, a large number of unnecessary surgical procedures are still performed. New diagnostics aids are emerging including the recent techniques of optical coherence tomography (OCT) which permits non-invasive 3D optical biopsies of biological tissues, improving patient’s quality of life. Nevertheless, the existing bulk or fiber optics systems are expensive, only affordable at the hospital and thus, not sufficiently used by physicians or cancer’s specialists as an early diagnosis tool. We developed an endoscopic microsystems based on Mirau interferometry and applied for swept source OCT imaging applied for gastroenterology. The architecture is based on a miniature spectrally tuned a single-channel Mirau interferometer integrated with an electro-thermal MEMS microscanner scanning the sample area.

Holography and tomography are imaging techniques, capable of producing 3-D images by image stacking and numerical refocusing, a spatially localized probing or by sample rotation. Usually, those methods are employed at visible range wavelengths of electromagnetic radiation. It is the simplest, most developed and most common approach since visible light is the part of electromagnetic radiation, which is the closest, by perception, to humans. There are, however, certain limitations to the visible light methods, such as diffraction limit in the range of hundreds of nanometers, the incapability of direct imaging of low-density objects, such as gasses, or the objects being completely opaque to the visible light radiation. Thus, the extension of those methods to the extreme ultraviolet (EUV) and soft X-ray (SXR) spectral ranges allows mitigating those problems. A few examples of such experiments employing EUV and SXR compact, tabletop laser plasma and capillary discharge sources will be presented and discussed.

Machine learning is an efficient tool to estimate input signals from the output ones for nonlinear systems. In case of object observation through scattering media with coherent illumination, the output signals could be speckle patterns highly disordered from the input ones. Even for the case, machine learning is effective to retrieve the input information. In the method, a number of pairs of input and output signals are used for training, and then untrained input signals can be retrieved from the observed output signals. We demonstrated object recognition, imaging, and focusing through scattering media and confirmed effectiveness of the presented method.

Spectroscopic holography refers to techniques in which the detected hologram contains information about specific species in the medium under study. In general, at least two lasers are required with wavelengths chosen carefully to fit the interaction process utilized. In this process, energy from the shorter wavelength laser beam is transferred to the longer wavelength coherently through the process of stimulated emission. Two interaction mechanisms are considered; Stimulated Laser Induced Fluorescence (LIF) and Stimulated Raman Scattering (SRS), which both are species specific with the ability of coherent interaction. In this paper, the fundamental properties of spectroscopic holography is presented and demonstrated with a few idealized experiments. These validation experiments are performed in a gas chamber in which different gases may be blended and the gas pressure changed between 1-12 bars. In addition, two examples of applications are presented. In the first set of experiments, LIF holography is used to image light absorption and laser heating in a dye simultaneously. The second set of experiments is performed in a ow of methane gas. It is demonstrated that the combination of holographic phase measurements and SRS gain images may be used for calibration. This calibration may further be used to measure absolute concentration in a burning flame.

Digital holographic microscopy (DHM) has proved to be a powerful imaging tool for identifying, analysing and reconstructing the 3D shape of cells and small organisms in their natural environment. In fact, DHM has the advantage, compared to other imaging techniques, to be a non-intrusive, non-destructive and label-free method for in situ measurements. This makes holography the most suitable tool for underwater imaging, where many of the species under investigation are very fragile and can be damaged. In particular, we built up an optofluidic platform based on DHM able to perform such analysis in microfluidic environment, i.e. in dynamic conditions and also in case of a turbid medium. In this work, we take advantage of this technique to identify, sort and reconstruct the morphology of different classes of microplastics (e.g. PVC, PET, PP, etc.) dispersed in water, which are among the major pollutants in the ocean, and to provide an effective assessment of their abundance. By adopting special algorithms for numerical processing of the acquired images, we try to separate the plastics from other materials, such as organic debris (shell fragments, animals parts, diatoms, etc.) and other items (metal paint coatings, tar, glass, etc.).

In some areas such as chemistry and biology it is of interest to have the ability to analyze transparent samples when they are subjected to changes or interactions with other media. In interferometry, these kind of tests are normally carried out with variations of a Mach-Zehnder layout where the object under study is in-line between the object beam and the camera’s sensor. The latter, results in a rather complex system difficult to align and that can easily saturate the sensor, among other experimental drawbacks. This invited talk presents a simple optical arrangement based on a digital holographic interferometer with an out-of-plane sensitivity, that allows the interaction of the object beam with the transparent sample only once without the need to have the digital camera aligned in-line with this beam. The use of a neutral backscattering screen avoids saturation in the sensor and introduces the possibility of being able to control the magnification/zoom used to inspect the sample. As proof of principle we present the results of the interaction of liquids with other liquids that have small differences in their temperature and density. The versatility and potential of the proposed interferometric system can be further explored by analyzing some chemical and physical reactions and their resulting optical phase.

Limited light source coherence can be both a complication and a benefit to interferometric optical metrology. Although high-coherence lasers are great for displacement measuring interferometry, holography, and Fizeau interferometry, many instruments rely on low coherence as part of the measurement principle. Examples include systems that separate parallel surfaces of transparent parts, coherence scanning interferometers for surface topography, and coupled-cavity fiber position sensors. In cases where high coherence is essential, there can nonetheless be a benefit to synthesizing reduced coherence to suppressing spurious fringes, coherent noise, and unwanted speckle.

High speed imagers record images at much higher speed than perceived by the human eye, but also enable to analyze it in different time bases. Recording is the keystone of sensor. It can either be embedded or remoted. The advantage of the onboard system mainly relies on the transfer speed to the in situ memory (including at the photon to charge conversion site). Its major drawback can be the onboard memory size limit. Remote storage requires the transfer of information very quickly to networks of high speed discs. If the main advantage lies in virtually infinite memory size, major drawback is the transfer speed between the camera and the external memory device. Choosing an appropriate high speed camera must be done by selecting, the maximum frame per second rate, minimum exposure time versus sensitivity and maximum recording time versus resolution and speed. Some imagers can now lead to 7kfps in relatively large resolution to 20kfps for reduced 1Mpixel images. Optics and light sources are important as continuous light require freezing the object movement by the camera exposure time, while pulsed source will remove the motion blur. For imaging, pulsed laser source in uncoherent radiation can even be used. Aperture of the optical system will determine speckle size or depth of field. Most of the imagers can be employed lensless for digital holography purposes. Small sensitive pixel will then be very attractive for this. This paper presents the recent developments and application in speckle light.

Shearography is a quite robust optical measurement technique frequently used for in-field testing. Defect inspections with shearography on fiber-reinforced plastics parts, widely used in aircrafts, ships, chemical and oil and gas industries, are often performed outside of the lab. However, environmental disturbances can make this task difficult or even impossible. Mechanical vibrations, air and thermal instabilities are among the most disturbing agents in harsh environments that can destroy the interference signal or, at least, dramatically reduce the interference signal quality, what raises the measurement uncertainty to unacceptable levels. For a successful testing, it is crucial to neutralize the influence of those agents. Compactness, high stiffness, robust mechanical design and an effective clamping system are very important design considerations to minimize the influence of those agents. However, the most effective solution is using a single-shot measurement technique; namely, acquiring a single image instead of a series of images. The exposure time is kept short enough to “freeze” any relative motion between the parts or drift of the measurement signal. This paper presents, describes and explores two configurations of multiple aperture single-shot shearography used by the authors for testing fiber-reinforced plastics used in the oil and gas industry outside the lab. The first one is a two-aperture setup variation based in an already existing configuration that produces carrier fringes on the speckle pattern and allows fringe processing in the 2D Fourier plane. The second one is a new three-aperture configuration that allows acquiring three fringe patterns simultaneously form three different shearing directions for each given loading state. A set of three wedges are used in combination with the three apertures to produce simultaneous shearing interferograms in three different orientations. One single shot image is acquired using a single high-resolution camera before a loading is applied to the specimen and another single shot image for each different loading levels. Since the resulting fringe patterns have carrier fringes in different orientations they are easily separated in the Fourier plane. Once the device has no movable parts and a single shot image is acquired, it is very compact, robust and can be successfully used outside of the optical bench. The paper presents applications of both devices. They have a great potential to expand the use of shearography for testing in harsh environments.

Numerical modeling tools are widely used in space science, but are usually limited to the thermomechanical steps. However, many payloads are equipped with high performance optical systems with tight tolerances. Therefore, experimental testing of space optics in very realistic conditions is a mandatory process. This experimental step is both time consuming and expensive. A multiphysics modeling tool that also takes into account the optical performances would therefore be an elegant solution to avoid these drawbacks. In this paper we compare some experimental results with numerical results obtained from a multiphysics suite. The local displacements of two space mirrors have been measured by use of electronic speckle pattern interferometry (ESPI) and the deformation itself has been calculated by subtracting the rigid body motion. After validation of the thermo-mechanical model, experimental and numerical wavefront errors are compared.

The modular design of steam turbines requires the welding of individual rotor discs to the finished single rotor. Conventional welding technology is very complex. Lack of fusion defects will occur after completion of welding and quality assurance is carried out by X-ray and ultra-sonic detection currently. Turbine rotors principally work at high temperature and therefore Ni superalloys are used to get those rotors manufactured. Fraunhofer institute IWS is currently developing a new welding technology based on laser-multi-pass-narrow-gap-welding (Laser-MPNG) including the implementation of a respective in-line quality assurance approach. For this approach, the nondestructive testing (NDT) i.a. Laser Speckle Photometry (LSP) was adapted to be applied in the narrow gaps of up to 200 mm in depth. LSP is an optical contactless, quick and quality-relevant NDT method, which will be used for characterization of material properties and defect detection, allowing process monitoring in many industrial fields. The LSP method is currently used at laboratory scale. For the transfer of LSP to an industrial level the LSP-setup and the evaluation algorithms need to be adjusted for in-line measurement during Laser-MPNG welding process. Additionally the results obtained by the LSP measurement was verified in the sense of a benchmark by simultaneously taking measurements with acoustic emission (AE) and ultrasonic technique (UT) and comparing the results with micrographs and visual inspection. This work presents the suitability of the LSP technique to monitor the Laser-MPNG welding and to detect defects less than 0.5 mm during the welding process.

This work presents the design and preliminary results of a high-speed shearography instrument in development for surface strain components measurements during an impact event. Composite materials are vulnerable to extreme dynamic loadings such as blade off events or foreign object damage as their mechanical properties are strain rate dependent. The development of new instruments to reconstruct extreme dynamic events will provide important insight into the understanding of the behaviour of composites. Shearography provides a quantitative measurement of the surface strain components with a high sensitivity as it is a non-contact interferometric technique. The current configuration of the shearography instrument realises measurements of the out-of-plane surface strain components during an impact using a double frame approach. The first experimental results reveal phase maps registered during an impact event with μs temporal resolution. Later the experimentally measured surface strain components will be used as input and validation data for new numerical and analytical models of the impact response of composites. The overall set of technical parameters of the developing shearography instrument makes it one of the most extreme applications of shearography for material characterisation.

Holographic imaging modalities are gaining increasing interest in various application domains ranging from microscopy to high-end autostereoscopic displays. While much effort has been spent on the development of the optics, photonics and micro/nano-electronics that enable the design of holographic capturing and visualization devices, relatively few research effort has been targeted towards the underlying signal processing. One significant challenge relates to the fact that the data volumes needed in support of this kind of holographic applications is rapidly increasing: for visualization devices, and in particular holographic displays, unprecedented resolutions are desired resulting in huge bandwidth requirements on both the communication channels and internal computing and data channels. An additional challenge relates to the fact that we are handling an interference-based modality being complex amplitude based in nature. Both challenges lead to the fact that for example classic data representations and coding solutions fail to handle holographic data in an effective way. This paper attempts to provide some insights that enable to alleviate or a least reduce these bottlenecks and sketch an avenue for the development of efficient source coding solutions. Moreover, it will also outline the efforts the JPEG committee is undertaking in the context of the JPEG Pleno standardization programme to roll out a path for data interoperability of holographic solutions.

The digital holography and holographic display constitute the best framework of 3D imaging as they aim to recreate the complete optical field emitted by a recorded scene. In this paper, we present two techniques of Fourier holographic imaging of real world objects. The first solution is an end-to-end full color Fourier holographic imaging approach, which involves standard RGB holographic recording an LED-driven viewing window display. It gives possibility of almost undistorted orthoscopic reconstruction of large real objects. Second architecture uses the same digital holographic content and horizontal parallax rainbow holographic display, which has reduced space bandwidth product requirements.

Digital holograms can be severely degraded by a mixture of speckle and incoherent additive noise. The problem is more severe in the case of IRDH, due to the large speckle grain. In order to suppress the speckles, here we present the MLDH-BM3D, a method specifically suited to filter DH images that combines Multiple DH captures, named Looks, to the BM3D, a numerical filter conceived in order to take advantage from a very sparse representation of the object features. We show that the joint action of ML and BM3D overcomes their respective limitations and achieves quasi noise free DH reconstructions.

The paper discusses the many opportunities for airborne digital holography, shows examples of current applications, describes different recording and data processing techniques, and suggests methods for improving and extending the technology.

An application of digital speckle pattern interferometry (DSPI) is demonstrated for the measurement of out-of-plane and in-plane deformations in the cortical bone of human maxilla at the bone-miniscrew implant interface. In the experiment, a dry human skull with dental arches and all teeth present was used. A miniscrew implant was inserted in the interradicular region of the maxillary second premolar and molar region with 45-degree angulation. The miniscrew implant was loaded by nickel-titanium coil retraction spring which induces deformation in the cortical bone around the boneminiscrew implant interface. DSPI system was used for the measurement of out-of-plane and in-plane deformations induced in the cortical bone. In DSPI, two specklegrams are recorded corresponding to pre- and post-loading of the retraction spring. The DSPI fringe pattern is observed by subtracting these two recorded specklegrams. The phase information is obtained from a single DSPI fringe pattern by using Riesz transform method. The obtained phase is used to measure the deformation induced in the cortical bone. The experiment was repeated for different miniscrew implants with various lengths and diameters. The experimentally obtained results reveal that implant diameter and implant length affect the deformation induced in the cortical bone layer at the bone-miniscrew implant interface. The experimental results show that by increasing the length and the diameter of the miniscrew implants reduces the deformation in the cortical bone.

The quality of an optical system forming a laser beam can be characterized through the measurement of aberrations in a deformed wavefront. The wavefront can be evaluated interferometrically in lateral shearing interferometer in which a coherent wavefront under test interferes with a laterally sheared wavefront copy. The resulted fringe pattern contain information on the first derivative of wavefront shape, according to direction of the shear. In this contribution we discuss the challenge related to wavefront shape reconstruction based on two lateral shearing interferograms from orthogonal shear directions. In case of not complicated wavefront the directional phase integration can be applied. Proposed method of reconstruction entirely omits this complicated process. It is based on calculations of the coefficients of Zernike polynomials from derivatives of wavefront shape and they are used for wavefront shape reconstruction. The utility of the proposed approach is tested numerically and demonstrated with characterization of aberrated wavefronts. Moreover, the simple configuration of lateral shear interferometer with two separated lateral shearing direction is introduced with context of monitoring of high power laser beam. At the end of the data analysis we apply an method for extracting the Zernike coefficients. The accuracy of implemented method is verified by characterization of generated spherical and highly aberrated wavefront. An error analysis indicates optimal conditions of measurements and proves high accuracy of developed method.

Holographic optical element (HOE) based digital speckle pattern shearing interferometer (DSPSI) is presented. The proposed DSPSI setup consists of volume phase holographic (VPH) grating combined with ground glass (diffuser) to shear the incident wavefronts. The shear of the two wavefronts is controlled by the distance between VPH grating and the ground glass. The sheared wavefronts on the ground glass are imaged on the image detector by an imaging lens. As both interfering wavefronts are of almost equal intensities, the contrast of the digital speckle pattern shear interferometric fringes is optimum. The proposed DSPSI setup is used for the measurement of temperature and temperature distribution in butane diffusion flame under the influence of magnetic field. In DSPSI system for the measurement of temperature in gaseous flames, two speckle interferograms are recorded: one in absence of the flame and another in the presence of the flame. These two recorded speckle interferograms are subtracted to get fringe pattern corresponding to the change in refractive index. The phase information is extracted from the experimentally obtained single fringe pattern by using Riesz transform method. The obtained phase information is used to calculate the change in refractive index and hence the temperature inside the flame under study.

Due to the special structural and functional properties, the advanced ceramic technology plays an important role in many areas of the industry. Fraunhofer IKTS develops novel ceramic materials for industrial applications, e.g. Na-β-alumina. These materials are used to produce high-temperature, low-cost ceramic batteries. In Na-β-alumina the defects occurs in production by extrude process. Therefore, defect detection is of great importance for quality assurance of ceramics for industrial applications, and advanced non-destructive diagnostic procedures are required. Laser Speckle Photometry (LSP) is an innovative optical non-destructive and monitoring technique based on the detection and analysis of thermally or mechanically activated characteristic speckle dynamics in the non-stationary optical field. Unlike other techniques based on speckle phenomenona, which concentrate on the distortion of whole speckle pattern or fringes, LSP is based on measuring spatial-temporal dynamics of laser speckles in near field, which focuses on the intensity change of each single pixel of camera sensor. The advantages of the new NDT method are, for instance, contactless, noninvasive, full field, fast, real time, high precision and sensitivity. The basic LSP setup has a simple but robust design to reduce the cost compared with other conventional NDT methods, and depending on its working principle, it can be integrated into in-line manufacturing process. The results of measurements will be presented by an imaging LSP method. At current research stage, the detectability of LSP for defects in ceramics is 300 μm in terms of length for crack and 200 μm in terms of diameter for pore.

The instantaneous out-of-plane displacement two-dimensional (2-D) maps associated to the scattering generated by the interaction of Rayleigh-Lamb waves with defects in plate structures can be measured using pulsed TV-holography (PTVH) and employed to characterize damage in non-destructive inspection applications. On the basis of visual comparisons we have shown previously that, except for the amplitude in the backscattering zone, a reasonable description of the measured experimental scattering patterns produced by holes both in harmonic and transient regimes can be obtained using the finite element method (FEM) combined with a 2-D model based on the scalar wave equation. In this work a systematic quantitative analysis of the agreement between FEM simulated maps and filtered experimental PTVH maps is developed considering both the spatial distribution of the local (pixel-wise) error in amplitude and phase and the corresponding global (averaged) errors over different areas in the 2-D image of the acoustic field. Changes produced in the experimental values by the speckle noise and variations introduced in the numerical values by the uncertainty in the characterization of the incident acoustic wave and the shape and position of the hole are characterized in order to obtain the net value of the error between theory and experiment.

A study in cortical bovine bones with collagen quality affectation by the air-dried technique is presented. An out of plane digital holographic interferometer is used to retrieve the optical phase during controlled compression tests on cortical bone samples. This test simulates physiological deformations in post-mortem healthy bone tissue and compares their surface response with those affected by the dehydration mentioned processes. Recent studies have demonstrated that bone strength must be understood as an integral concept that depends on quantity, quality and turnover of the bone. Considering that several diseases and conditions could affect not only the inorganic (hydroxyapatite) but also the organic (collagen and water) components of the bone, it is critical to isolate each affecting effect during the optical tests. Water comprises about 20 % of the bone’s volume and is a key determinant of its structural mechanical behavior, i.e., it is responsible for giving the collagen its ability to confer ductility or plasticity to the bone. The results presented in this talk analyze the micro structural variations of the bone strength due to the resulting optical phase variations as obtained from the tested bulk samples. Several tests were performed to register the profiles and ranges of the displacements during the compressive loads which are expressed in terms of wrapped optical phase. A discussion is presented.

A new configuration of a transmission digital holographic interferometer to observe micro scale samples is presented. The optical system uses high magnification to analyze the phase of semitransparent biological samples in order to measure their size. As proof of principle some previously characterized pollen grains are placed in the object’s beam path and magnified by projection on the neutral phase screen whose image is conveyed on the camera sensor and thus is used to retrieve the optical phase that is related to the size of each particle. As validation fluorescence and transmission images from a confocal microscope are used to compare the phase intensity retrieved with the interferometric system. Results show a direct relation between the pollen size and the resulting phase magnitude after geometrical processing with the advantage of having a micrometric measurement with a simple optical set up.

In this paper, we analyze the image quality reconstructed by holographic display depending on spatial coherency and temporal coherency of the light source in holographic display system. The simulation was conducted by changing both spatial coherency and temporal coherency independently using proper modeling of coherency. A holographic display setup was composed to verify simulation results. LED and LD were respectively used as a light source for holographic display, and the quality of reconstructed images reproduced by using LED or LD was compared. The scheme of near-eye holographic display adopting LED as a light source which generates low speckle noise but narrow depth range was proposed. The proposed scheme of near-eye holographic display system was verified experimentally.

Digital holography is widely known as one of the techniques reconstructing a depth profile of the object. For digital holography (DH), the light source that has a long coherence length such as laser or laser diode is generally recommended. Recently, digital holographic microscopy (DHM) utilizing light emitting diode (LED) as a light source has attracted attention. However, it has to satisfy certain conditions for LED be utilized in off-axis DHM as it has small coherence length. Due to this fact, the hologram cannot be captured from the other side of a beam splitter. Therefore, we propose an LED-based off-axis reflective DHM that combines a 4-f system that optically relays the field to the sensor plane of charge-coupled device (CCD). We analyze the reason why the sample plane has to be relayed by 4-f system. We provide experimental results to verify the necessity of relay optics in LED-based reflective off-axis DHM.

Composite materials are continuously being developed for all kinds of applications, making an impossible task to test each one during their development. The main purpose of these new and advanced materials is to improve the physical and mechanical properties of two or more materials by combining them. Without this combination each material by its own does not meet the specifications that the composite one will. New composite materials are subject to several types of tests trying to predict their behavior under specific chemical and mechanical conditions. In this work we deal with the mechanical characterization under a controlled compression test in circular composite probes. The use of a home-made specifically designed testing machine for non-destructive optical testing allows repeatable and controlled compression loads. Associating this testing machine with the well-known analysis capabilities of digital holographic interferometry in high speed mode, makes it possible to register and analyze the precise instant where the composite samples develop a crack by compression, its propagation and finally the fracture formation. A series of composite samples with three different concentrations of metallic particles (reinforcement) within the polymer (matrix) were manufactured. These specimens were subjected to a controlled compression and the obtained interferometric results show that it is possible to estimate an unknown particle concentration density of the composite material by identifying the load value when the crack appears. The latter is possible if a data base of similar samples are characterized before and then the crack load point is correlated to estimate this reinforcement.

This paper presents an application of laser speckle imaging method to characterize the kinetic growth of Bacillus thuringiensis (Bt). Numbers of parameters, such as speckle grain size and spatial contrast, are considered in order to characterize the culture medium and to monitor in real time the fermentation process. We show that the grain size and the contrast of the speckle image decrease with the increase of the cells concentration. The correlation of speckle results with optical density measurements shows the effectiveness of dynamic speckle for real-time monitoring of Bt cells growth kinetics.

We present an experimental study of the method using a spatial light modulator for correction of the wavefront reflected from the optically rough surface. This method is based on the detection of the mutual phase differences between different regions of the wavefront that correspond to the constructive interference. We study the capabilities of this method from the metrological point of view for the ground glass samples characterized by several different levels of roughness. The resulting wavefront correction is tested in dependence on the measurement parameters settings and is verified by analyzing two specific patterns generated by the spatial light modulator.

We present a novel approach to 4D (XYZ + time) body scanning, developed for supporting medical rehabilitation monitoring. The system reflects the actual requirements for 4D measurements, providing a feature of capturing up to 120 Hz sequences of point clouds, with a spatial resolution of 1.0 mm and inaccuracy of 0.5 mm. The presented system consists of four directional modules arranged evenly around the measurement volume to provide complete scans. A structured light method is utilized, therefore each directional module consists of detectors and projectors. In order to enhance body surface coverage from every direction each measurement module uses two detectors and a single projector. This configuration is a result of optimizing the best scanning results considering proper amount of data and a reasonable number of hardware elements (that translates into system price). For the chosen number of directional modules a problem of synchronization (projected patterns overlapping is highly erroneous) was solved. We decided to apply spectral separation in a form of colored projection and color filters. This solution allows each detector to register only the pattern associated with it. A single frame pattern for structured light method was used to achieve presented measurement frequency. A set of algorithms was developed in order to perform all processing steps, including phase unwrapping, based only on a single image per detector. The final phase distribution is scaled into XYZ coordinates, therefore an extended common calibration process was introduced to receive a single multidirectional cloud as the output. The system is able to reconstruct dynamic objects in the form of point clouds, where each point, aside from XYZ coordinates, also contains an information about it’s normal vector. The future work will include improving the system accuracy and error-resistance.

In this work we demonstrate wavefront complex modulation of semiconductor light sources via digital micromirror device (DMD). Proposed holographic configuration allows to correct the aberrations caused by the imperfections of the DMD and the optical elements. We consider the blazing effect of the DMD surface and configured the optimal condition of the optical setup for certain DMD and the wavelength of the radiation source. The technique was approved with the experiment of obtaining different kinds of wavefront distributions from the semiconductor laser with high M2 factor.

Holographic tomography (HT) enables nondestructive, quantitative measurement of three-dimensional refractive index distribution of transparent, weakly-scattering micro-samples. The method has been successfully applied for inspection of technical objects, as well as biomedical specimens. The key element of the HT measurement is acquisition of multiple holograms corresponding to various projection directions. In the conventional configuration of HT, this is achieved by rotating a sample, which provides high and almost isotropic resolution of tomographic imaging. However, the major disadvantages of this configuration is degradation of the reconstruction quality due to inaccuracies of the sample rotation. In this paper, we propose a novel autofocusing solution, which enables compensation of the rotation errors in HT. The method utilizes cross-analysis of two optical fields that were registered for special combination of the illumination and rotation angles. The proper selection of these parameters ensures redundancy of information in the fields, which here is used for quantitative evaluation of the misalignment error. Notably, the proposed solution is fundamentally different than other alignment methods for HT. Those methods utilize autofocusing algorithms that assume a single in-focus plane of a sample. Contrarily, our solution does not disregard the 3D character of a sample and thus is compatible with tomographic measurements. The utility of the proposed alignment method is validated with numerical simulations using two examples of complex samples with large axial thickness: a set of beads and Shepp-Logan phantom.

Computerized Aided Design (CAD) and Computerized Aided Manufacturing (CAM) ceramic occlusal veneers are increasingly used as therapeutic options. However, little is known about their mechanical behavior under stress, as the response of the prepared tooth that supports it. The aim of this article is to use for the first time 3D color holography to evaluate the behavior of a molar occlusal veneer under stress and the response of the prepared tooth. The occlusal surface of a lower molar is prepared to receive a specific monolithic ceramic reconstruction manufactured with a chairside CAD/CAM system. Longitudinally cut samples are used to get a planar object observation and to “look inside” the tooth. A digital holographic set-up permits to obtain the contact-less and one-shot measurement of the three-dimensional displacement field at the surface of the tooth sample; stain fields are evaluated with low noise-sensitive computation. The results show an excellent behavior of the restored tooth without areas of excessive stress concentrations, but also a significant involvement of the dentin enamel junction. So, we demonstrate that the ceramic occlusal veneer seems to behave in accordance with the biomechanical concepts ensuring the longevity of the reconstituted tooth. It follows that we demonstrate that 3D holography is a highly recommended method for studying dental biomechanics.

Digital holographic microscopy (DHM) is actively investigated in the field of bio-imaging as a quantitative phase microscopy. In recent years, digital holographic technique for enhancing the spatial resolution using speckle patterns has been reported by several research groups, and we reported the enhancement of the spatial resolution in DHM using speckle illuminations generated from a ring-slit aperture. In this study, by applying the two-wavelength method to DHM using speckle illuminations, we realize the enhancement of spatial resolution and the extension of measurement range of shape measurement in DHM.

We designed, realized, and tested a pocket module that allows performing off-axis Digital Holography microscopy with no need for an interferometer setup. A commercial plastic chip is engineered for the scope. Our strategy is moving complexity from the reconstruction algorithms and the external imaging apparatus to the chip itself, using custom optical components. We functionalized the chip with a photoresist grating and polymer lenses, to avoid the need for a reference arm as well as external optical components. Thanks to the single beam scheme, the system is robust against vibrations and the stability of fringe patterns implies enhanced portability.

Defocused laser speckle photography is used as a tool to measure the heat responses in a titanium component during laser heating. The evolution of the response is compared with a set of preprocessed Finite Element Simulations of the corresponding process with the aim to verify the simulation model and to find the simulation settings that best resemble the experimental results. The titanium component consists of a 300 x 100 mm₂ substrate of thickness 3.2 mm on which a 200 x 30 x 11 mm³ ridge is built up using the laser metal deposition by wire process. The component is heated on the top of the ridge by a 300 W laser for 10 s and the deformation of the subtrate is followed throughout the heating-cooling cycle. The simulated deformation gradient is shown to resemble the measured response, and the magnitude of the response indicates that about 70 % of the laser power transferres into heat in the metal.

In this work is exploited the possibility to use Electronic Speckle Pattern Interferometry (ESPI) for the characterization of different tyres with particular attention to the tyres shoulder section. Tyres characterization is of fundamental importance for vehicle dynamics modelling, since they are the main responsible of vehicles dynamical behaviour and thanks to their ability to deform, they allow to drive a vehicle generating the appropriate interaction forces at the interface with the road. Their behaviour is a consequence to their very complex structure. Two different racing tyres, one for car and other for motorcycle, have been considered. The investigation has been focused at the aim to evaluate and measure the section’s components in order to get accurate information about the different layers along through the tyres shoulder section. Here we demonstrate that the different layers (rubber, nylon, steel) can be easily highlighted and identified by mean of the ESPI that, thanks to its high sensitivity, is capable to estimate the different out of plane displacement of the different layers that respond in a different way (i.e. with a different deformation) to a thermal stimulus highlighting the layers themselves. Moreover, we introduce a de-noising step in the reconstruction process: in particular we enhance the wrapped phase information by using a suitable algorithm called SPADEDH. It is important to note that the assessment about the different layers along the section is a very difficult task to obtain by visual inspection or classical microscopy. In fact, the condition of the cutted surface, or rather the strong inhomogeneity and the roughness make impossible to obtain good images especially in the shoulder area.

Mycoplasma synoviae (MS) infection in poultry is a serious global epidemiological and economic problem. Usually, MS pathogen is responsible for respiratory disease, infectious synovitis and the eggshell apex abnormalities (EAA). The EAA may lead to an increase in the incidence of cracks and breaks of eggshells which often are reason of microbial infections and higher water vapor loss during the entire incubation process. All these problems can cause higher embryonic mortality and lead to significant economic losses. Most of eggs with EEA posses characteristic deformation of an eggshell, however, a number of those eggs infected by MS may be omitted during visual inspection. To prevent such situation a combined Full-Field OCT (FF OCT) and spectral technique for detection of MS infected pieces is proposed. After a numerical processing from a recorded transmittance spectra of a eggshell a few parameters are calculated. Those parameters describe the shape of the transmittance spectrum understood for example as the directional coefficient of a line matched to a graph, or maximum amplitudes of changes in a specified range of wavelengths. Analyses of those parameters allow shells assignment into one of two groups – eggs coming from healthy and MS infected poultry. Data obtained from FF OCT allow more precise evaluation of MS influence on the eggshell, for example changes in the micropores, which are responsible for proper embryo – environment gas exchange [1]. Authors present a new approach to food quality testing which in near future may be applied to reduce the egg production losses caused by MS in the commercial poultry industry.

Skin cancer is one of the most common forms of cancer and thus a big public health problem worldwide. However, although it is well known that UV radiation is the main cause of skin cancer, there are currently only a few quantitative studies about the effects of UV radiation on the skin. One of the main objectives of the research project we are conducting is centered on the study of the change in elasticity and/or stiffness that the skin suffers after being irradiated with UV, parameters that are being analyzed and quantified with the aim of using these elasticity properties as a powerful clinic tool. Preliminary studies on the elasticity of animal skin samples aged inside a UV radiation chamber were conducted using Digital Holography Interferometry, a non-invasive optical technique that has been gaining importance as an alternative way to study elasticity properties, mainly due to its sensitivity and precision for measuring displacements and strains. Controlled sound waves were used to stimulate the skin samples, with the results suggesting that the longer it is exposed to UV radiation the greater is its increase in stiffness, confirming the importance of not selfoverexposing to solar radiation. The research work proposed in the project represents a great opportunity to contribute to the knowledge of other skin diseases as well as skin cancer. A deeper analysis of the change in elasticity between healthy skin and skin with cancer will be discussed in a later publication.

The pointwise intensity-based processing of time-correlated speckle patterns allows for detection of activity in threedimensional objects by building a two-dimensional map of a certain statistical parameter. We have developed in this work reliable approaches for high-quality visualization of the activity map through normalization and preprocessing of the captured raw data. As a first task, we analyzed statistical behavior of correlation-based estimates to show erroneous determination of activity under non-uniform illumination or varying reflectivity across the object surface for nonnormalized algorithms and wrong detection of zero-activity regions for the normalized algorithms. Next, we proposed solution for the non-uniform illumination issue by using the sum of the speckle patterns at a given time lag for normalization and by introducing a flexible threshold to form binary patterns. We checked the option of the spatial smoothing of the raw data for activity map visualization enhancement and proved that smoothing in the temporal domain was more effective. Efficiency of the proposed preprocessing for data captured at uniform and non-uniform illumination was demonstrated on synthetic and experimental speckle patterns.

In this paper we propose and implement the systematic approach to investigation of skin tissue based on sequential determination of refractive index and dry mass density for representative skin cells (3T3 fibroblasts and HaCaT keratinocytes) during their growing in a culture from single cells up to formation of a single layer. The main measurement tool is digital holographic microscopy supported by reference measurements performed by holographic tomography. The results of the measurement are presented and discussed.

Limited angle optical diffraction tomography is a technique that allows for non-destructive and quantitative analysis of biological samples directly from Petri dishes and microscope slides. Recently, a new reconstruction method, called Generalized Total Variation Iterative Constraint (GTVIC), was proposed. It is an iterative modular technique that calculates the reconstruction without the errors that are otherwise present due to limited angular range of projections. Unlike other similar techniques, GTVIC is dedicated to biological structures that have non-piecewise constant refractive index distribution. However, GTVIC is sensitive to local deviations of the immersion refractive index from its nominal value. Such deviations are present due to e.g. dust or cellular debris in the measurement volume. Therefore, we propose a method for preprocessing of a sinogram that numerically removes unwanted objects from the measurement volume without affecting the investigated object and its diffraction pattern. The described method is found useful in any tomographic algorithm that utilizes support constraint in the reconstruction process.

Holographic tomography (HT) is a measurement technique utilizing refractive index (RI) as imaging contrast and enabling wide spectrum of applications in modern cell biology. Obtained 3D RI distribution within a sample is quantitative, however it is prone to phase measurement and numerical errors especially in the case of limited angle holographic tomography (LATH). Therefore, determination and control over metrological parameters of HT system is crucial for credibility and usefulness of obtained results. In this work we propose a new type of calibration 3D phantom for LATH that allows to determine accuracy of a tomographic system. We have experimentally verified that it is possible to design, fabricate (using two-photon polymerization method) and measure complex microstructure containing regions of constant, step-like and gradient RI distribution. The phantom printing parameters required to obtain the reference RI values are determined based on its measurements using well-established 2D techniques (digital holographic microscope and white-light interferometry). The final calibration structure printed with multiple RI levels is measured by full angle HT as the reference method for LAHT. The advantages and limitations connected with implementation of the proposed phantom are discussed.

We have developed so far the method for imaging simultaneously blood flow and blood concentration change in skin tissue by using two-wavelength near infrared laser speckle patterns. We conducted experiments for human volunteers to confirm the feasibility of the method for estimating temporal response in the blood flow and blood concentration change in a human finger to occlusion on a human arm with different pressures from 50 to 150 mmHg. The results demonstrated that the response may depend on individual minimum and maximum blood pressure values.

In the paper a concept of an optical vortex application for the secure optical system was presented. The proposed system uses a spatial multiplexing of optical signals performed by creating two separate communication channels in one optical fiber in which the important data can be encrypted. The optical secure system consists of three parts, i.e.: light beam generator, optical fiber link and demodulation unit. Light from a single source is split into two types of light beams. One of them remains unchanged and preserves its Gaussian shape. The other one is transformed to an optical vortex by passing through the liquid crystal spiral phase plate. This liquid crystal cell requires spatially distributed electrodes which can be supplied independently to introduce spatially distributed phase shifts what changes this Gaussian beam into optical vortex. It was applied as a perdeuterated liquid crystal D5CB which has a small absorption in telecommunications’ spectral region. Both beams are coupled together to the specially designed photonic crystal fiber which supports propagation of fundamental and vortex modes launched to it. The cross section of the optical fiber has a honey comb lattice with two types of air-holes rings. External one with four rings confines all propagating modes and internal single ring which spatially separates the fundamental mode and the first group of higher order modes. Both types of spatially separated modes can be used for transmitting important data. The fiber link output requires a second spatial demodulator to decouple both modes and decrypt transmitted data. At this stage of the project a light beam generator is developed, fiber link and demodulation unit are under testing.

An iterative algorithm for sparse-angle optical diffraction tomography in 2D is proposed, which combines elements of the gridding reconstruction technique with the classical scheme of Fourier data consistency iterations subject to non-negativity constraint, additionally supplemented with gradient-domain and wavelet-domain sparsity constraints. The initial gridding step together with a heuristic replenishment method for convolved data points serves to minimize the Fourier-domain interpolation errors while keeping very low oversampling factors, here 1.375. In the considered 2D case this setting leads to reduction of memory use by factor 2 and faster convergence without sacrificing reconstruction quality when compared to results relying on nearest neighbor mapping. The algorithm is tested numerically in 2D with noiseless synthetic data simulated through the Fourier diffraction theorem in a way that prevents nonphysical wrapping of the projection fields within the detector frame. A modified Shepp-Logan phantom is tested together with a custom phantom created from an integrated phase image of a living cell for a set of 32 and 17 projections in full angle. The results indicate that the combination of TV and wavelet based priors is effective with both types of objects. Also, simultaneous use of the two priors always outperforms each of them applied separately. However, the optimal balance between their parameters can vary significantly with different objects and projection sets.

In the paper the advantages of two different microscopic techniques, namely digital holographic microscopy (DHM) and Confocal Laser Scanning Microscopy (CLSM) have been combined with the aim to investigate HeLa cell culture in terms of statistical analysis of area of subcellular structures of HeLa cells and related to them dry mass estimation. To assure the proper statistical representation of the cells both measurements comprised of multiple fields of view (FoVs), stitched together to form two FoVs with overlapping regions. The results suggest a strong linear correlation of nucleoli dry mass to their projection area, a result that is promising in terms of its biological relevance.

We demonstrate the non-invasive investigation of circulating human breast adenocarcinoma cells in microfluidic environment by implementing the full-angle tomographic phase microscopy (TPM). The proposed approach lies in a completely passive optical system, i.e. avoiding mechanical scanning or multi-direction probing of the sample and exploiting the engineered rolling of cells while they are flowing along a microfluidic channel.

Shearography can be used for full-field strain measurements in the field of vibration analysis. It provides the spatial derivative of the optical phase difference of the vibration modes amplitude along the so-called shear direction. The shearographic setup considered here is based on the phase-shifting time-averaged technique. It can easily be applied experimentally, but its drawback is that binary phase patterns are obtained. These phase changes are related to the zeroes of a Bessel function. Retrieving the corresponding displacement maps is not straightforward. Moreover, integration of shearographic results need to be performed, and this step is sensitive to noise in the patterns. In this paper, different processing stages are described, from fringe denoising to integration of the displacement maps. The application on data acquired in industrial environment illustrates the good performances of the proposed method.

In this experimental study we present full methodology for investigation and evaluation of high power laser induced damage and its influence on structural integrity of polymer structural sandwich composites (PSSC) samples covered with various colour paint coatings. The work includes in-situ quantitative monitoring of out-of-plane and in-plane displacements and strains by 3D digital image correlation and temperature fields - by thermovision. The experiments are supported by material reflectance studies and post-mortem, microscopic crater investigations. Conclusions concerning influence of structural core and colour coating on PSSC performance, their structural integrity and laser lethality are presented.

Kinoform is a synthesized phase diffractive optical element which allows to reconstruct image by its illumination with plane wave similarly to hologram. Unlike hologram however, kinoform forms only one diffraction order containing reconstructed image. There is no analytical solution to kinoform synthesis problem; various iterative methods providing relatively small synthesis error are used instead. However, with limitation on quantity of addressable phase levels this error becomes significant. Another factor affecting reconstructed image quality is speckle-noise inherent to coherent illumination. There is common solution to speckle-noise problem – repetition of kinoform or hologram several times along each dimension in order to reduce size of image pixels so that they do not overlap with each other. This greatly reduces amount of speckle-noise, but leads to formation of grain structure in resulting image. We eliminate this disadvantage by synthesizing several kinoforms with sparsed image. In each case image is shifted relative to previous one. So that when all kinoforms are sequentially displayed on spatial light modulator with sufficiently high frequency, reproduced images merge into one. Resulting image is relatively speckle-free and does not have grain structure. Furthermore, because each individual kinoform has vast amount of free dark space, it can be used to dump synthesis noise similar to dummy-area technique but with free space between informative pixels. Results of optical experiments are presented.

Imaging deep inside the tissue still remains a challenge for all microscopic techniques. Imaging using coherent illumination is even more challenging due to unwanted effects like speckle formation causing significant loss of imaging contrast. In our work we propose a solution to this problem by controlling the spatial distribution of phase of light illuminating the sample. In newly developed optical set-up the beam illuminating the sample first is passing through SLM that enables to fully control projected light patterns. The interferometric setup enables to perform 3D full field OCM imaging. We present the results from controlled wavefront illumination and its ability to image through scattering layers. The ultimate goal of our techniques is to create new imaging method applicable for biological 3D imaging in turbid medium.

In holographic tomography obtaining projections is the key part of the measurement process that enables the 3D refractive index reconstruction. The error of the illumination angle can significantly influence the reconstruction quality and alter the result degrading the reliability of the reconstruction. Thus, in this paper the impact of the scanning errors in limited angle holographic tomography with respect to two reconstruction algorithms is analyzed. The simulated errors are compared to the errors identified in the experimental system. The reconstruction errors are verified using a paramecium cell phantom at the simulation stage and with a biological object, namely a macrophage cell in the experimental part. The experimental system presented in the paper exhibits maximum expected measurement errors found in galvanometer-mirror-based holographic tomography setups.

The process of information recovering from fringe pattern can be divided into two main parts: filtration (fringe pattern background and noise removal) and phase (or amplitude) demodulation. In recent years the 2D Hilbert spiral transform (HST) has become one of the most popular phase demodulation techniques. Together with empirical mode decomposition used for fringe pattern preprocessing forms a strong fringe pattern analysis algorithm called 2D HilbertHuang transform (HHT). Variational image decomposition was recently adapted for fringe pattern filtration. In combination with the 2D Hilbert spiral transform and after some modifications it might become an excellent tool for fringe pattern analysis purpose and can compete with well-developed HHT. Proposed modification is the first attempt to automate the variational image decomposition in terms of fringe pattern filtration. Received results show that VID-HST can compete with HHT and may become an excellent alternative for fringe pattern evaluation. Another fact encouraging the development of VID is a wide range of applications that have been proposed up to now, i.e., image denoising, fringe pattern filtration and phase filtration.

The depth-of-field (DOF) characteristic of the imaging system with scattering medium is analyzed based on the analytical model of ambiguity function as a polar display of the optical transfer function (OTF) in this paper. It is indicated that the scattering medium can help re-collect more high spatial frequencies, which are normally lost with defocusing in traditional imaging systems. Therefore, the scattering medium can be considered not as an obstacle for imaging but as a useful tool to extend the DOF of the imaging system. To test the imaging properties and limitations, we performed optical experiments in a single-lens imaging system.

The aim of this work is to develop a holographic method that provides the shape reconstruction with high, interferometric accuracy and an extended measurement range. The method requires recording of a set of n holograms obtained for selected combination of illumination angles θ𝑛. The difference between the optical phases corresponding to on-axis φ0 and offaxis φ𝑛 fields allows calculating the object height. To maintain high-accuracy evaluation of height the dedicated shape reconstruction algorithm is proposed. The algorithm consists of n steps, each with several substeps. Each substep is divided into: (1) calculation of the height from φ0 and φ𝑛 ; (2) propagation of the optical fields. In this paper, the proposed algorithm is numerically validated using three types of objects.

Rapid development of machine learning techniques opens new application fields for Unmanned Aerial Vehicles technology, which include detection and classification of objects. It is possible to detect buildings, vehicles or various objects present near pipelines and industrial buildings. In some cases, such as monitoring of the critical infrastructure, accuracy of the detection is crucial. 2D data classification enables detecting an object and determining its basic parameters. 3D data, that can be obtained from drones, supplement 2D data, and can significantly increase the accuracy of detection and classification of objects. It also bares additional information and can simplify determination of dimensions of already classified objects. Furthermore, some objects, difficult for classification using 2D images, can be easily classified with 3D data. Such objects are for example: excavations in the ground, objects partially overshadowed by trees or fully covered by dried leaves. 3D data collected by drones is typically obtained with SfM (Structure from Motion) and Lidar (Light Detection and Ranging) methods. SfM provides three-dimensional data from the photos that have been collected for 2D analysis. The advantage of this method is high quality texture. The main problem is that this method is not useful for night flights due to lack of feature points on images. Lidar is a laser measurement method using data on the time of flight of a laser beam reflected from an obstacle (object). It allows to obtain 3D data in all light conditions. However, collected data does not have color information. The combination of both methods will provide dense and accurate point clouds with texture, which can be consequently used for detection and classification of objects. In this paper a pipeline for acquisition, merging and processing of 3D data gathered by drones is presented. The first step is to obtain assembled point clouds from Lidar in one coordinate system using GPS data. Then Lidar point cloud is integrated with SfM point clouds. 3D data generated this way also includes coordinates of camera in the moments when SfM photos were collected. The full 3D model of monitored area containing GPS coordinates and positions of camera may be used to simplify configuration of a supplementary flight in order to measure places where no measurement data was obtained or the density of point cloud was too low. Having a point cloud of the reconstructed object prepared in such way, it is possible to compare point clouds, features extracted from point clouds and geometry of already classified objects over time.

Grating Interferometry well known also as High Sensitivity Moiré Interferometry is the optical method for in-plane displacement and strain measurement. The sensitivity of this method depend on spatial frequency of the diffraction grating attached to the object under test. For typical specimen grating, with spatial frequency 1200 lines/mm, the basic sensitivity is 0.417 μm/fringe. On the other hand, the high sensitivity makes the measuring range to small for many applications in experimental mechanics and material engineering. In the paper the simple idea for decreasing sensitivity of the Grating Interferometry by using the gratings with lower spatial frequencies of 100 - 200 lines/mm is presented. Additionally, in this case the measurement sensitivity can be controlled by matching the illumination angles to the higher diffraction orders of the gratings, e.g. for grating frequency 200 lines/mm, the basic sensitivity is 2.5 μm/fringe for the first and 1.25 μm/fringe for the second diffraction orders. Such sensitivities can be delivered by other optical techniques, e.g. Digital Image Correlation but the Grating Interferometry has the unique feature - the specimen grating "remembers" its initial state. It means that all successive measurements have the same reference (moment when the grating is attached to the object surface) what allows to obtain information about the cumulative displacement between any measurement periods and monitoring the state of the object under test at any time. Theoretical analysis of proposed technique and concept of the Decreased Sensitivity Grating Interferometer design are described and discussed.

The experimental results on the application of the dynamic speckle-interferometry technique in studies of micro-and macroprocesses occurring in high-cycle fatigue of metals and in live cell are presented. A brief theory of the method and its metrological characteristics are described. The process of the surface alteration in macrocrack initiation was studied using a Charpy-notched sample. It was shown that the processes of the crack formation at the notch tip and the tightening formation at some distance from the tip are simultaneous from the very test start. The secondary plasticity zone emerges after the crack initiation. The reaction of cells to ECHO11 virus was studied on a monolayer of cultured RD cells. It was shown that there is a substantial difference in the dynamics of the speckle images of the cells infected with ECHO11 virus and herpes simplex virus type 1.

We address a non-invasive imaging method to observe dynamic objects hidden behind a turbid medium. An initial image of the objects is first recovered by speckle correlation technique (SCT) with a single shot speckle pattern. The scattered point spread function (PSF) is then extracted by taking a deconvolution process between the initial image and its corresponding speckle pattern. Consequently, the images of the dynamic objects, within the optical memory effect (OME) range, can then be reconstructed directly with the same deconvolution process between the sequential speckle patterns and the estimated PSF. In addition, a further calibration operation is employed to enhance the robustness of the PSF, ensuring sharp images can still be observed when objects are close to or even cross the edge of OME. Experimental demonstration is presented to verify the feasibility of our proposed method.

In the paper we investigate hologram binarization method through time multiplexing based on histogram. In the proposed approach input object is divided into N components with equal total intensity distributions. Next, propagation and binarization procedure is employed for each component separately. Presented method is matched to DMD application since it modulates the input light simply by reflection. In the computer simulations the quality of the reconstructed holograms with the proposed method is compared with that of the threshold method for different reconstruction distances. Additionally, efficiency of the technique is verified experimentally during optical reconstructions performed in the holographic display with DMD and LED illumination.

In this work, we investigate numerical models of selected spatial light modulators (SLMs) to provide an accurate simulation of diffractive effects present in optoelectronic hologram reconstruction, i.e. DC term and higher orders. We focus on reported most influential parameters: (a) fill factor, (b) amplitude modulation of dead space (effect of surface structure between adjacent pixels), (c) phase of dead space (phase modulation profile between adjacent pixels), (d) spatial influence of adjacent pixels on phase modulation value, and (e) number of phase quantization levels. The impact of each factor on modeled diffraction efficiency and orders distribution is investigated. We consider phase-only reflective models of LCoS SLMs on the basis of commercially available architectures. Additionally, the pixelated SLM model is tested on the example of two practical cases.

With state-of-the-art 3D measurement systems, short-wave structures such as tool marks cannot be resolved directly inside a machine tool chamber. Up to now, measurements had to be performed outside the machine tool. We present an interferometric sensor that carries out such measurements inside the machine tool, which saves time-consuming and expensive setup procedures. Our sensor HoloCut uses digital holography as measurement principle. By the use of multiple wavelengths, we get a large unambiguous axial measurement range of up to 2 mm and achieve micron repeatability, even in the presence of laser speckles. With a lateral resolution of 7 μm across the entire 20 x 20 mm² field of view, both macro- and microstructures (such as tool marks) are measured with an axial resolution of 1 μm. Consequently, this qualifies HoloCut for in-situ measurements and integration in a machine tool. In this paper, the boundary conditions of integrating interferometers inside a machine tool are evaluated. Occurring vibrations and limited available space are particularly challenging constraints: The optical and mechanical design of HoloCut is introduced along with numerical correction algorithms: A piezo-stage setup is used to induce known displacements. Using these algorithms, measurements even with a closed-loop control of the machine tool head activated are demonstrated on a coin measurement. The use of HoloCut is motivated on the base of the daily operation of a 5-axis machine tool: We present an evaluation of an exemplary ISO 25178 parameter Sq using HoloCut measurements and compare those with reference, yet not inline-capable systems.

Classical time-averaging is widely used for MEMS/MOEMS dynamic behavior investigations. In order to evaluate the information on maximum amplitude at a given load of vibrating object one needs to evaluate the argument of Bessel function that encodes the useful information. For this purpose many different approaches were presented. Among them Temporal Phase Shifting applied to Bessel fringes is of special interest since it provides most accurate results. It, however, requires additional cumbersome pixelwise correction routine via specially designed look-up-table. In this paper we investigate, through extensive numerical simulations, the possibility of reduction of phase evaluation error (without correction routine) by different strategies of phase shifting. Two different 5 step algorithms are investigated for that purpose. Additionally, quick and robust correction procedure based on evaluated phase distribution is presented.

Based on a previously devised speckle-based set-up for probing minute wavelength changes for a coherent field [1], [2] we will here present the first experiments where these changes are resolved on a millisecond time scale. The setup is based on probing the lateral shift of a speckle pattern arising from a slanted rough object, the speckle displacement being linearly proportional to the wavenumber change. Thus, by shearing the speckle pattern across a grating-like structure [3],[4] and [5], a frequency proportional to the frequency of the wavelength change can be derived as will the irradiance. Thus, a cordial display of the complex field amplitude may be obtained with a high temporal resolution and a reasonable spectral resolution. The spatial filter is here preliminarily implemented by recording the speckle pattern with a CMOS array with subsequent digital image processing mimicking the use of a spatial filter.

Multiwavelength digital holography enables precise and fast 3D height measurements of rough surfaces. To inspect objects during motion would enlarge the range of applications enormously. In this work the limits of this technique with respect to velocity and inclination angles are studied for linearly moving as well as for rotating objects. We demonstrate measurements on surfaces with inclination angles of up to 40° , moving linearly with a velocity of 2 mm/s, providing 2 μm accuracy, and on a rotating cylinder with circumferential speed of 10 mm/s, we achieve 1.1 μm precision. All measurements are conducted with less than 1 mW of continuous-wave laser light, so the object moves several micrometers during exposure time.

Measuring scratches, nicks and dents on precision machine parts is a challenge for industry, especially when the parts have to be tested on the factory floor or in the field, far from any metrology laboratory. A new system that combines dynamic interferometry with structured light enables the projection and analysis of polarization-based virtual fringes in a single camera frame. This very compact system, the metrology setup is flashlight-sized, is capable of micrometer precision, yet is immune to vibration, which enables handheld operation in a variety of environments. This paper will discuss the technical approach to achieve vibration-immune 3D measurements and will present a variety of performance tests and a discussion of practical applications of the system.

The emerge of super-resolution (SR) microscopy enabled imaging below the diffraction barrier. One of the SR techniques, Stimulated Emission Depletion (STED) microscopy, has shown promise in super-resolution imaging of thick specimen. Imaging such structures is a non-trivial task due to the increased aberrations introduced by the sample. Adaptive optics provides the solution to this problem. AO can correct the aberrations by modulation of the phase. Although STED microscopy is theoretically a diffraction unlimited technique, the resolution limiting factor is noise. Modern filtering techniques, such as block matching and 3D filtering (BM3D), can increase the signal-to-noise ratio of the STED images. This work presents an AO 3D STED microscope with aberration correction and background noise filtering using BM3D algorithm. We show the super-resolution images of thick samples and emphasize the importance of image processing for recovering of object high spatial frequencies.

The evaluation of the characteristics of a dental restorative material is based on several criteria such as the ability of the material to resist to potential degradation, its durability, the stress it exerts on the residual dental structures, its resistance to surface wear, and its resistance to fracture. All these important factors must be taken into account and tested when developing a new dental restorative material. Glass ionomer cements (GIC) possess unique properties, including adhesion to tooth structure, bioactivity and fluoride release. The objective of this study is to evaluate by analyzing the dynamics of the polarized speckle field how GIC samples, prepared according to two different methods and conserved in water at 35°C, deteriorate.

Glass-ionomer cements (GIC) belong to the class of materials known as acid-base cements. The drying process of these materials and the evolution of their physical properties play an important role in the quality and durability of dental care. Since monitoring these processes contributes to the improvement of the knowledge on these materials, we aim in our work to monitor in real-time hardening of GIC using dynamic speckle. Speckle images are temporally analyzed by computing the temporal correlation coefficient. The temporal correlation curves present a Lorentzian profile, which characteristics vary during GIC hardening process.