To experimentally analyze the morphological characteristics and to predict the resulting scattering patterns of different
bacterial colonies, an optical morphology analyzer was constructed based on a laser confocal displacement meter to
simultaneously obtain the optical properties of colonies. The profile data was accurately captured using the confocal
laser triangulation technology and the transmitted light was collected by a photodiode circuit. The analog signals were
read into a data acquisition board in parallel for off-line signal processing. This approach showed promising results for
differentiation of micro-colonies in the range of 100~300 μm based on the morphological differences among different
species using light scattering.
Bacterial colonies play an important role in the isolation and identification of bacterial species, and plating on a petri dish is still regarded as the gold standard for confirming the cause of an outbreak situation. A bacterial colony consists of millions of densely packed individual bacteria along with matrices such as extracellular materials. When a laser is directed through a colony, complicated structures encode their characteristic signatures, which results in unique forward scattering patterns. We investigate the connection between the morphological parameters of a bacterial colony and corresponding forward scattering patterns to understand bacterial growth morphology. A colony elevation is modeled with a Gaussian profile, which is defined with two critical parameters: center thickness and diameter. Then, applying the scalar diffraction theory, we compute an amplitude modulation via light attenuation from multiple layers of bacteria while a phase modulation is computed from the colony profile. Computational results indicate that center thickness plays a critical role in the total number of diffraction rings while the magnitude of the slope of a colony determines the maximum diffraction angle. Experimental validation is performed by capturing the scattering patterns, monitoring colony diameters via phase contrast microscope, and acquiring the colony profiles via confocal displacement meter.
In order to maximize the utility of the optical scattering technology in the area of bacterial colony identification, it is
necessary to have a thorough understanding of how bacteria species grow into different morphological aggregation and
subsequently function as distinctive optical amplitude and phase modulators to alter the incoming Gaussian laser beam.
In this paper, a 2-dimentional reaction-diffusion (RD) model with nutrient concentration, diffusion coefficient, and agar
hardness as variables is investigated to explain the correlation between the various environmental parameters and the
distinctive morphological aggregations formed by different bacteria species. More importantly, the morphological
change of the bacterial colony against time is demonstrated by this model, which is able to characterize the spatio-temporal
patterns formed by the bacteria colonies over their entire growth curve. The bacteria population density
information obtained from the RD model is mathematically converted to the amplitude/phase modulation factor used in
the scalar diffraction theory which predicts the light scattering patterns for bacterial colonies. The conclusions drawn
from the RD model combined with the scalar diffraction theory are useful in guiding the design of the optical scattering
instrument aiming at bacteria colony detection and classification.
Early detection and classification of pathogenic bacteria species is crucial to food safety. The previous BARDOT
(BActeria Rapid Detection by using Optical light scattering Technology) system is capable of classifying the bacterial
colonies of around 1~1.5mm diameter within 24~36 hours of incubation. However, in order to further reduce the
detection time and synchronize the detection operation with the bacterial cultivation, a micro-incubator is developed that
not only grows bacteria at 37°C but also enables forward scatterometry. This new design feature enables us to
continuously characterize the light scattering patterns of the bacterial colonies throughout their growing stages. Some
experimental results from this new system are demonstrated and compared with the images obtained from phase contrast
microscopy and a confocal displacement meter to show the possibility of earlier identification of bacteria species.
Moreover, this paper also explains the updated optical and mechanical modules for the beam waist control to
accommodate the smaller bacteria colony detection.
Shack-Hartmann Wavefront Sensor (SHWS) recently has been extensively researched for optical surface metrology due
to its extendable dynamic range compared with the interferometry technique. In our institute, we have developed a
digital SHWS by adopting a programmable Spatial Light Modulator (SLM) to function as a microlens array and replace
the physical one in the traditional configuration of this sensing system. In this paper, we proposed to use the developed
system for the relative measurement of toroidal surfaces, which are widely used in many optical systems due to their
unique optical features of different curvatures in X and Y directions. An innovative idea to design the diffractive
microlens array implemented by SLM was presented to tackle the measurement challenge. This unconventional design
approach has a great advantage to provide different optical powers in X and Y directions so that focusing spots can be
formed and captured on the detector plane for accurate centroid finding and precise wavefront evaluation for 3D shape
reconstruction of the toroidal surface. A digital Shack-Hartmann Wavefront Sensing system with this unique microlens
array was built to verify the design concept, and the experimental results were presented and analyzed.
Since its emergence in the early 1970s, Shack-Hartmann Wavefront Sensing technology has been investigated and
explored world-widely by the researchers and engineers. However, there are few papers or reports to study the system
performance and key factors to affect the performance of a Shack-Hartmann Wavefront Sensor (SHWS), in this paper,
through experimental study of the system stability of a SHWS, it is found that the image sensor and detector, normally a
CCD, should be placed exactly at the focal plane of the lenslet array, otherwise it will bring in significant wavefront
measurement error. In order to improve the system performance, a special lenslet array with long focal range is designed,
and it is functioned by a spatial light modulator for sampling wavefront in a SHWS. Diffractive lenses with long focal
length range can provide pseudo-nondiffracting beams, and a long range of focusing plane. The performances and effects
of the modified SHWS with such a special lenslet array generated by a programmable SLM, are investigated, and the
experimental results show that the system stability and measurement repeatability are not sensitive to the sensing
distance, and can keep at a good level in a long range.
An improved second generation digital image watermarking scheme is proposed. This scheme exploits the region feature instead of point or line feature. The region features are retrieved by watershed transform, which allows watermark recovery after common attacks. The experiments have shown that this proposed scheme is robust against compression, noise intrinsically and more robust against geometrical attacks and JPEG compression compared with Kutter's method. The watermark capacity is improved because the robustness of region feature is more than point or line feature.
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