This PDF file contains the front matter associated with SPIE Proceedings Volume 12672, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

Although glass objects for artistic and utilitarian purposes were present during Roman times and earlier, optical metrology was practically non-existent prior to the emergence of spectacles. Glasses to improve human vision first appeared in Italy around 1280, and some progress in understanding fundamentals of optics was made after that date and during the renaissance. It was not, however, until 1608 with the invention of the telescope in Holland, that the long evolutionary development of optical metrology as a specific scientific discipline began in earnest. The Author traces classical methods of optical metrology from the 17th century telescope era up to the mid-20th century, with emphasis on optical systems for reconnaissance, surveillance, and astronomy. The Author’s hands-on experience in quantitative optical metrology began shortly after World War II with military surplus optics, followed by the construction and testing of numerous telescopes between 6 and 16-inches aperture during the 1950s. The 1960s brought extensive testing and evaluation of lenses at the optical laboratories at Wright-Patterson AFB, Ohio and elsewhere, continuing through the early days of laser metrology in the mid-late 1960s and afterward. This paper presents examples of testing lenses and cameras for USAF, DoD, and NASA to include those used in the Gemini and Apollo Programs. Special emphasis is placed on classic resolving power testing with large collimators and special test cameras using aerial photographic films. Closing comments will stress impacts for later-era digital sensors, high-speed computers, and metrological lasers.

Optical metrology is a driving force in advancing industries ranging from consumer electronics to components for energy and transportation. Despite this progress, there is considerable wasted effort attributable to misleading instrument specifications, inconsistent calibrations, and ambiguous data processing procedures. Confusing statements of accuracy and uncertainty, inconsistencies in filtering and parameter calculations, and misunderstandings about measurement principles and limitations undermine confidence in measurement results. A greater awareness and use of international standards documents can improve the situation, leading to a wider adoption of optical methods. At the same time, there is a critical need for stronger engagement in the development of new standards by experts in optics and photonics.

A major challenge in thermal analysis at the nanoscale for semiconductor materials lies in determining the mass of the sample. Samples for nanocalorimetry are usually deposited directly onto the chip sensor, but the mass and density of these thin films is hard to quantify. In this work, laser doppler vibrometry is used to measure the complex modes of the nanocalorimetry chip sensor membrane. The sample produces a frequency shift in a selected mode, which can be measured using a simple non-contact optical method.

This investigation proposes a method for absolute surface determination in a coordinate measuring machine (CMM) with a planar extension of 200 x 200 mm² which is based on the measurement of two spatial gradient fields. The gradient field data was obtained by measuring a test mirror in two equidistant shifted positions along two orthogonal axes while the reference mirror stayed in a steady position. The comparison of experimental data measured in an area of 192 × 192 mm² showed a small root-mean-square deviation of 5.3 nm between the reconstruction result and a regular measurement result. For an a priori estimation of the influence of experimental error sources on the reconstruction deviation, simulations of the measurement process were carried out. Alongside determining the optimal measurement strategy, the focus was investigating positional and orientational deviations of the test surface caused by the shifting motions. While the translational deviations have a subordinate effect, the simulated results show that small orientation deviations around the motion axes cause high reconstruction deviations. To eliminate the motion-induced share of the gradient fields orientation a separation from the topography intrinsic share, which has to remain part of the data, is necessary. This is achieved by the combination of the high-precision design of the mechanical shifting stage and the implementation of an additional boundary condition in the data processing using a least square algorithm.

The effects of the misalignment of a test surface in a deflectometry system were explored. A Stewart Platform Hexapod stage was used to create the intentional misalignment, rotate the test surface position around the X and Y axes as well as displace their Z location. The measured surface maps were analyzed in coefficients of a fit of the surface map to the Zernike coefficients. The Zernike term results were adopted to show the relationship between the induced pose changes and the reconstructed surface map. Such an understanding of the errors in location and orientation and deflectometry measurement results would be beneficial in the future measurement of ophthalmic optics with a deflectometry system.

In this paper, we present an optical setup which estimates the radius of curvature of spherical surfaces with the aid of Fizeau interferometry. While the use of Fizeau interferometry to achieve these measurements is wellunderstood in prior art and commercially deployed, we propose a variant of Fizeau interferometry for the same measurements. Our proposed method deploys electronically-controlled tunable focus lenses to perform cats-eye and confocal beam scans with a motion-free scanning system as opposed to a motion-based laser scanning and repositioning system. Eliminating motion from a surface scanning system mitigates system breakdowns related to bulk mechanical motion of optical elements. It also promises to reduce the system cost as well as bulkiness of such interferometric systems. We show the proposed system improvement via the use of a standard tunable focus lens on a legacy commercial Zygo surface curvature measuring system. We demonstrate the operation of the proposed system with experimental data and results using lenses and curved mirrors as samples. For all samples, we compare our measurements from the actively-tunable Fizeau interferometer to baseline measurements from the same original Zygo system using its own zoom lens. The experimental results show an excellent agreement between measurements from the motion-based legacy commercial system and the actively-tunable bulk motionfree system. Future work would focus on characterizing sample surface aberrations by subtracting wavefront aberrations imparted by the tunable focus lens piece.

A dual-mode on-machine metrology system has been developed to address the critical demand for on-machine metrology in precision optics fabrication. The system can measure both surface form and roughness simultaneously, without requiring the reconfiguration of the optical path to switch between laser interferometer mode and LED interference microscopy mode. It can achieve snapshot high-precision phase-shifting measurement, minimizing the impact of environmental disturbance. With its compact design, the system makes on-machine metrology feasible in diamond turning machines, avoiding errors caused by removing, repositioning, and balancing the workpiece. With the compact and dual-mode features, it makes on-machine tool alignment and surface characterization possible, avoiding off-line testing and significantly increasing process efficiency.

Dynamic light scattering (DLS) is a technique used to characterize the size of nanometer and sub-micrometer particles in colloidal suspensions. Its non-destructive nature and simple usage make DLS widely applied in fundamental research, research and development (R&D), and quality control processes. While it is not uncommon to encounter the need to measure highly concentrated samples, the applicability of DLS is normally constrained by multiple sample and setupdependent factors. MicroDLS, an optical microscope-based DLS design, has emerged as an effective alternative to measure highly concentrated or heterogeneous samples. Based on microDLS as a platform, we have been developing a method to improve the time resolution of measurements to further apply DLS to time-evolving systems. Herein, we performed various explorations of parameters to test the practical limit of applications by microDLS. Our setup is built based on a confocal optical microscope, a 532nm CW laser, a time-correlated single photon counting system, and a custom post-processing data analysis methodology. We explored the effects of the type of microscope objective and sample concentration on the measurement quality. The measurement of 60nm and 220nm polystyrene particles in suspension at different concentrations, showed the existence of an optimum working concentration range. Finally, the contrast between microscope objectives (20x NA0.4 and 4x NA0.1 air) revealed the specific technical challenges and limitations for each case.

The systems employ line-scan fiber-based surface characterization and temperature monitoring based on the two-color pyrometer through the fibers for different wavelength radiation. The proposed system offers a promising approach for SLM process monitoring, providing valuable information for process monitoring and control, leading to improved part quality. The integration of surface characterization and temperature measurement into one system can be used to optimize process parameters, reduce manufacturing costs, and enhance SLM process understanding.

Optical metrology methods such as structured light, triangulation and diffractive methods all rely on the properties of the light source used. Spatially coherent sources provide for small focus spots, but also pronounced surface scatter. There are more options today for metrology light sources than ever before from a wide range of laser diodes, LEDs and super-luminescent diodes available today in many wavelengths, powers and coherence properties. For some applications that use interference effects, high coherence is critical where others that rely on signal peak and phase may be degraded by the coherent effects such as speckle prevalent with most lasers. This paper will explore the use of laser diodes, LEDs and super-luminescent diodes (SLDs) for several metrology applications including interference and structured light methods and present practical results and limitation for with each source.

We have previously presented our work in developing and applying a commercial digital holographic microscopy (DHM) system for volumetric, 3D characterization of bacterial motility. The system was applied to simple biological systems, i.e., single bacterial species, to demonstrate its effectiveness. We are now applying DHM to more realistic conditions, including multiple bacterial types, to differentiate the species of interest for investigating their interactions. Our workflow for species classification and motility characterization combines DHM and machine learning. Specifically, our DHM instrument acquires holograms of single bacterial species and mixtures of different species, the software extracts in-focus images of individual bacteria and their trajectories, and deep convolutional neural network models are constructed and trained using the in-focus images and then deployed to the mixture data for classification. The motility and morphology of the predicted species in the mixture is consistent with the measurements from isolates, verifying the effectiveness of the developed workflow. This work showcases the application of DHM to investigate complex biological systems.

Growing awareness of the adverse health effects of nitrogen oxides has increased the demand for reliable, sensitive and mass-producible sensor systems. Photothermal interferometry has shown great promise towards sensitive, selective and miniaturized sensor solutions. This work describes the development of a macroscopic photothermal sensor system with a sensor head consisting of a low-cost, custom-made and fiber-coupled Fabry-P´erot etalon. The sensor was tested with NO₂, achieving a 3σ limit of detection of 2.5 ppmv (1 s). Exhibiting little drift, a limit of detection of 100 ppbv is achievable for 200 s integration time. Compensating for the low excitation power, the normalized noise equivalent absorption was calculated to be 2.2 × 10⁻⁸ cm⁻¹W/ √ Hz. The sensor system is not limited to NO₂, but can be used for any gas or aerosol species, by exchanging the excitation laser source.

This study presents a method for reconstructing the full-aperture wavefront, particularly at the edge-side wavefront in Quadri-Wave Lateral Shearing Interferometry (QWLSI). While QWLSI is a powerful method for measuring wavefront error in an optical system, it faces the challenge of obtaining wavefront information on the non-interfering region on the edge side of the input beam by lateral shearing. This challenge becomes more significant for larger apertures. To address this, the study proposes a modified method for reconstructing the full-aperture wavefront using the basic principle of partial slope detection in lateral shearing interferometry (LSI). QWLSI provides four directional two-point slope functions by wavefront shearing. The inverse LSI slope can be deduced using the spatial relation between the reconstructed center wavefront and the measured slope information. The partial edge-side wavefront can then be reconstructed using this inverse equation, following the four-shearing direction. Finally, the partial edge-side wavefront maps can be combined using a phase stitching algorithm to obtain a full-aperture wavefront. The effectiveness of this method was demonstrated through numerical simulation and experimental results, which showed that the proposed method accurately reconstructed the noninterfering edge-side wavefront in QWLSI, improving the spatial range of wavefront measurement. This technique has potential applications in optical testing, particularly in improving the efficiency of large aperture mirror testing by reducing the margin diameter of the mirror blank preparation. The study introduces the reconstruction method in detail and presents some testing results for verification.

We present the experimental results of the proof of concept of a metrology instrument developed to characterize the cryogenic mirror of the Einstein Telescope (ET) prototype. ET is a proposed gravitational-wave observatory. The metrology instrument uses the principle of low-coherence interferometry to measure the local change in topology and local induced vibrations of the mirror resulting from the cooling down process. We implement an innovative optical phase mask and a microlens array to obtain a depth map of the mirror on a single camera frame. With our instrument prototype, we can obtain 25 interference patterns of the same mirror spot for each camera frame. Each interference pattern corresponds to a difference Optical Path Difference (OPD). Then by reconstructing the interference patterns, we can measure the mirror’s local topology change and local induced vibration. Moreover, in this proceeding, we describe the analysis of the white-light interference patterns through numerical simulations and depict the metrology instrument’s optical design. Finally, we discuss how we can use the metrology instrument for real-time characterization of other optical components with all the advantages of white light interferometry.

The optical interferometric technique with polarization phase shifting has been realized as one of the most important techniques for optical non-contact measurements. However, the measurement of thin film thickness using field emission scanning electron microscopy (FE-SEM) or scanning electron microscopy (SEM) has been inconvenient due to the high cost of maintenance. This research aims to measure the thickness of the Hole Transport Material Nickel (II) oxide (NiO) layer deposited on a glass substrate (NiO/FTO layer) using phase shifting in a Sagnac interferometer. In the experimental setup, the signal is split into the FTO reference arm and the NiO/FTO sample arm using a nonpolarizing beam splitter. The split signals are then detected through a balanced photodetector. By analyzing the signal intensities at polarization settings ranging from 0° to 90°, the phase shift and thickness of the NiO layer can be determined. In this study, a NiO thickness value of 281.64 nm was successfully achieved. To evaluate the accuracy of the proposed measurement method, the percentage error between the proposed technique and the conventional SEM method was computed. The percentage error was found to be 0.23%. These results indicate that the proposed setup holds promise as a cost-effective alternative to SEM for measuring thin film thickness.

In hospitals but also in other public facilities, it is essential to minimize the risk of contagion from infected persons. One of the key aspects is therefore to avoid contact infections caused by touching contaminated surfaces. While the current practice of wipe disinfection carried out by cleaning staff is expedient, it makes objective documentation difficult, can lead to surface damage by sanitizer overdosage, and can even put people at risk due to the released vapors. Consequently, it would be beneficial to implement technical solutions for both efficient and gentle disinfection of surfaces, e.g., a mobile platform with a sanitization module attached to a robotic arm. For a targeted cleaning and disinfection, which is tailored to specific objects and materials, such a system requires sensor technology for analyzing the environment. With this purpose in mind, we have developed a multimodal 3D sensor for detecting objects that can typically be found in a hospital environment. We started by examining specific materials using a spectrometer as well as cameras of various spectral ranges. Based on the results, we developed a sensor that can provide multimodal surface data with high spatial and temporal resolution. In experiments, we investigated how the generated data stream can be utilized for the targeted identification and treatment of typical hospital objects.

Binary pseudo-random array (BPRA) artifacts are useful devices for calibrating the instrument transfer function (ITF) of interferometric microscopes and other optical and non-optical surface and wavefront measurement instruments. The intrinsic white noise character of the power spectral density function of the artifact simplifies the deconvolution of the ITF from the measured power spectral density (PSD). However, resampling of the BPRA intrinsic artifact features with the measurement tool’s specific sampling pattern modifies the white noise character of the intrinsic spectrum and needs to be accounted for in the ITF-based data deconvolution process. We have developed an analytic solution to the spectrum of a resampled one- and two- dimensional BPRA. The resultant nominal PSD function is a simple two-parameter cosine function with a period equal to the resampled pixel width. A transfer function model for interferometric microscopes that incorporates this function, along with an ITF that includes aliasing effects and variable numerical aperture (NA), wavelength, and obscuration factor, is used to fit to the BPRA PSDs measured by an interference microscope for a range of objective and zoom lens magnification combinations.

The use of artificial intelligence (AI) software for wavefront sensing has been demonstrated in previous studies. In this work, we have developed a novel approach to wavefront sensing by coupling an AI software with an Autostigmatic Microscope (AM). The resulting system offers optical component and system testing capabilities similar to those of an interferometer used in double pass, but with several advantages. The AM is smaller, lighter, and less expensive than commercially available interferometers, while the AI software is capable of reading out Zernike coefficients, providing real-time feedback for alignment. Our AI software uses an artificial neural network (NN) that is trained to output the Zernike coefficients, or any other relevant figures of merit, exclusively from synthetic data. The synthetic data includes random Zernike coefficients for a parametric description of the wavefront, noise, and a defocus error to avoid any stringent accuracy requirement. Once trained, the NN yields Zernike coefficients from a single frame of defocused intensity. The feedforward architecture of the NN enables swift output of Zernike coefficients, eliminating the need for iteration or optimization during run time. Using the software with an AM allows for paraxial alignment of the object in the test cavity, with the real-time Zernike coefficients guiding the item into optimal alignment. This double pass test is not possible with most other types of wavefront sensors, as they are designed for single-pass use. Our results demonstrate that the test results obtained compare well with modeled results, and that errors in the AM can be removed by calibration, as in the case of interferometer transmission spheres. Furthermore, the simple defocused image of a source provides non-ambiguous phase retrieval, which competes with traditional wavefront sensors such as Shack-Hartmann (SH) sensors or interferometers. The AI software provides high dynamic range, sensitivity and precision. This novel approach to wavefront sensing has significant potential for use in a wide range of applications in the field of optics.

PMMA is widely used in aquariums, windows of planes and submarines, and even scientific experiments like the Jiangmen Underground Neutrino Observatory (JUNO). Residual stress in PMMA has an important influence on its craze, creep and lifetime. The novel detection equipment of residual stress of PMMA was developed using spectral measurement and analysis technology based on the principle of stress birefringence and Wertheim's stress-optical law. There are two advantages of the novel detection equipment - the optical path difference is obtained through multi-wavelength spectral analysis instead of single-wavelength analysis, and the measurement accuracy of residual stress is better; the detection equipment can not only analyze PMMA samples in laboratory, but in actual engineering.

This paper introduces a methodology for simultaneously conducting multi-component 3D measurements in highspeed turbulent afterburning flames using several spectral plenoptic cameras. Traditionally, plenoptic imaging techniques capture the 3D scene using a single camera, where the camera is modified to include a microlens array that is located between the primary lens and the sensor. Each pixel behind a microlens encodes angular information onto the sensor by sampling a point on the main lens. A multispectral plenoptic camera is a combination of a plenoptic camera with a spectral filter array at the primary lens aperture plane. Thus, spectral information is encoded onto angular information, such that the camera captures spatial, angular, and spectral information of a light-field in a single-snapshot, which enables multiple measurements to be performed using discrete spectral bands from a single camera. Additional cameras provide improved performance by extending the overall range of angular information captured. Experiments were conducted using three spectral plenoptic cameras to capture subsets of the following measurement within a sonic hydrogen flame and subsonic ethylene flame: tomographic particle image velocimetry; dual-wavelength pyrometry of particle-laden flow; and 3D measurement the chemiluminescence of CH*. This work demonstrates the ability to simultaneously capture multiple 3D measurements with views from as few as three multispectral plenoptic cameras, whereas traditional cameras could require an order of magnitude more sensors.

This work demonstrates as a novelty the generation of lossy mode resonances (LMR) in uncoated optical fiber with high index cladding (HIC), without use of an additional high refractive index thin film. For this purpose, commercially available double cladding fiber (DCF) having W-type refractive index profile was chosen for the purpose and spliced between two multi-mode fibers at the two ends. Here, the outer cladding of DCF fiber is having higher refractive index than the inner one which allows to generate LMR phenomena. The LMR phenomena can be tuned by changing the thickness of the outer cladding of DCF fiber e.g., by using chemical etching. The resulted fabricated device is characterized towards surrounding medium refractive index, demonstrating the sensitivity of about 1100 nm/RIU in RI range of 1.33-1.39, further making such devices suitable for bio-chemical sensing. This novel sensing becomes an alternative to other thin film based optical fiber sensors due to advantages in terms of simplicity, cost and stability.

In our method, we calibrate the high-resolution frequency domain optical coherence tomography (FD-OCT) spectrometer using a single mode fiber optic Michelson interferometer coupled with a broadband super-luminescent light emitting diode (SLED) source, used in the very same FD-OCT system. The SLED light is filtered by the Michelson interferometer and exhibits equally spaced in the frequency domain fringes. The spacing of these fringes is controlled by the difference in arm's length of the spectrometer. By performing measurements for several values of differences in optical paths between arms in Michelson interferometers we find the nonlinear dispersion of the grating spectrometer. We use this dispersion when employing the FD-OCT system as a distance gauge.

This work explores combining the reference sphere and nulling hologram for freeform measurements by using a nulling reflection hologram in a Fizeau geometry. To do this, we combined standard phase shifting with an iterative algorithm to solve for errors in the phase steps, obtained a phase surface, and ultimately fit it to a set of Zernike polynomials. Preliminary results show that we can characterize a surface via Zernike coefficients using in situ holographic exposures followed by a sequence of interferograms using small (<100μm) values of lateral shear.

Due to the negative diopter lens constructions of conventional remote sensing catadioptric telescopes, the corrector lens produces divergent optical property, resulting in difficulties of measuring the center thickness of the lenses and the air gaps between lens interfaces. One solution to address this issue is to incorporate a positive diopter lens on the image side during the optimization of remote sensing catadioptric telescope lenses and thus the lens center thickness as well as interlens surface air gap distances can be measured accurately from the image side by low-coherence interferometry. In this study, the lens center thickness and inter-lens center surface air gap distances of an enclosed corrector lens was measured in a single scan by using non-contact in situ measurement method of low-coherence interferometry and resulted in a significant advancement in the assessment and verification process. It facilitated the determination of whether the corrector lens met the required specifications of remote-sensing instrument during the process of assembly, integration, and successive environmental testing.

In this research, we developed a surface inspection system based on Phase-Measuring Deflectometry for specular surfaces. PMD is a non-contact, full-field optical measuring technique that measures the phase shifts caused by surface deformations. While PMD has seen significant advancements and increasing use in various industries due to its simple configuration and moderate precision, uncertainties in alignment and calibration can limit the practical performance of the system for industrial applications. To address this, we propose a system that measures freeform optical surfaces smaller than 50x50 mm2 using stereoscopic redundancy to eliminate height ambiguity. We apply self-calibration methods to maintain measurement precision below sub-micrometer level. Our measurement results of specular surfaces demonstrate a measurement precision of less than 0.1 um, with excellent convenience and less throughput time.

By measuring scattered light, our goal is to improve the accuracy and automation of manual inspection. In this study, we attempted to measure the non-contact surface roughness of the curvature surface of a round bar sample by capturing and analyzing the scattered light distribution. We also evaluated the influence of machining marks on the round bar. A round bar workpiece (cold forged material, surface polished) was irradiated with a He-Ne laser (spot diameter Φ0.8 mm, maximum power 8 mW, wavelength 632.8 nm) and a PIN photodiode (sensor size Φ1.5 mm) was scanned to acquire the scattered light intensity distribution. The detected scattered light distribution was fitted to a scattered light distribution model based on the generalized Harvey-Shack theory to calculate surface roughness parameters. The extracted roughness parameters are root mean square roughness ”Rq” and half width of autocovariance ”lc”. The PIN photodiode was scanned in the direction of the machining striations and in the direction orthogonal to the striations, and the ratio of the lc in the two directions was used to evaluate the surface roughness anisotropy parameter ”Str”. By determining ”Str”, we can consider the effect of machining striations on machine performance. This paper presents the results of the evaluation of Str compared to the conventional method, which allows non-contact, non-destructive measurement.