This PDF file contains the front matter associated with SPIE Proceedings Volume 12216 including the Title Page, Copyright information, and Table of Contents.

An important challenge in infrared imaging today consists in addressing the SWaP problem (Size, Weight and Power), for example by simplifying as much as possible the optical system before the sensor. The work presented in this paper takes advantage of recent techniques in femtosecond laser direct writing to imprint optical systems. We want to simplify an infrared multispectral imaging system, which combines a lens array and a filter array. This work aims at merging a lens array with a filter array by writing gradient index lenses with a femtosecond laser inside a dedicated glass substrate. A classical gradient index requires a huge refractive index variation, which cannot be reached today with femtosecond laser processing (Δ𝑛𝑚𝑎𝑥 ~ 0.05). So, we decided to turn towards writing a gradient index Fresnel lens. A first-order Fresnel lens was designed with a Δ𝑛𝑚𝑎𝑥 < 0.05 discretized into 8 index levels to guarantee a diffraction efficiency of 85% on the overall spectral bandwidth of the filters. The multispectral design is made of an array of 2x2 Fresnel lenses in a landscape lens configuration. For a horizontal field of view of 40°, each GRIN Fresnel lens has 82 rings inside a total diameter of 3.8 mm. After characterizing the photosensitive response of the material to fs-laser writing, we started writing the first prototypes of graded index Fresnel lenses. For a first approach, a discretization on 4 index levels was chosen. A focal length measurement has been performed in order to compare it with our model.

Laser structuring is a powerful tool for functionalizing surfaces, e.g., improving the tribological properties. To achieve small structures in the < 2 μm range, microscope objectives are typically used in laser material processing. There are two main challenges to achieve small structures: On the one hand, the limited working distance between the focusing optics and the workpiece results in a comparatively small processing area of a few square millimeters. On the other hand, the depth of field is limited when structuring with microscope lenses due to their large numerical aperture. As a result, the intensity of the laser beam is strongly dependent on the position in the propagation direction, so that the process window for material removal is only a few μm and small deviations disrupt the process. For highly productive large-area laser structuring in a roll-to-roll (R2R) process, the processing area must be enlarged, and the depth of field must be increased at the same time to enhance process robustness. With a given R2R process speed of the moving material of 2 m/min, and a material width of 0.5 m, we want to structure an area of 1 m²/min. The structuring pattern is a hexagonal arrangement of spots with a spot diameter of 1-2 μm and a spot distance of 2 μm. Additionally, we want to achieve a depth of field of 45-50 μm to enhance the process robustness. Given this background, this paper presents an approach in which a laser beam is split into numerous sub-beams and these sub-beams are subsequently shaped in such a way that the depth of field is increased for each individual beam. For beam shaping, a combination of static optical elements is used to transform a uniform into a Bessel-like intensity distribution to achieve a greater depth of field. By a skillful arrangement of the focusing elements, structure sizes of 1-2 μm as well as structure distances of 2 μm are achieved with the given R2R process speed.

Wave Front Phase Imaging (WFPI) is a new wafer shape measurement technique that acquires millions of data points in just seconds or less, on a full 300mm silicon wafer. This provides lateral resolution well below 100μm with the possibility of reaching the lens’ optical resolution limitation between 3-4μm. The system has high repeatability with root-mean-square (RMS) standard deviation (σRMS) in the single digit nm for the global wafer shape geometry and for nanotopography it reaches in the sub ångström (Å = 10-10 m) range. WFPI can collect data on the entire wafer to within a single pixel away from the wafer edge roll off1. The flatness of the silicon wafers used to manufacture integrated circuits (IC) is controlled to tight tolerances to help ensure that the full wafer is sufficiently flat for lithographic processing. Advanced lithographic patterning processes require a detailed map of the wafer shape to avoid overlay errors caused by depth-of-focus issues2. In this paper we go deep into the theoretical explanation as to how the wave front phase sensor works.

The SpectRx system has been developed to measure sphero-cylindrical spectacle lens power as an alternative to clinical lensmeters. This work was inspired by the ongoing global pandemic, which limited physical access to eye care facilities for regular eye exams. The SpectRx system aims to bypass this limitation by providing at-home prescription measurements. The power and orientation of the spectacle lenses are obtained by the use of readily available objects such as a cell phone camera, a displayed or printed target, and a fixed-dimension magnetic stripe card. The magnification of the lenses can be calculated by examining the image captured through the lens of the target at a fixed distance. The magnification may be spatially varying due to the cylinder component of the lens. Processing the pictures captured with a cell phone camera is done automatically with standard image processing algorithms. The processed images, in turn, are used to calculate a clinical prescription, i.e., Sph/Cyl×Axis. The SpectRx may expand access to quality eye care in not only the current pandemic situation but also in locations where eye care may not be easily accessible, such as some rural or remote areas. The image processing and clinical prescription calculation are discussed here.

A Powell lens is a unique optic that projects a line output profile from a collimated laser with its output characteristics dictated by the input beam and geometry of the lens. The goal of this work was to demonstrate that a Powell lens can be used to shape the output of the broadband source to be complimentary to the input of a passive line scanning hyperspectral spectrometer. In this paper the use of a Powell lens with a broadband white light source is demonstrated to produce a similar output when compared to a monochromatic source. Output from a tungsten halogen lamp was collimated and transmitted through a Powell lens with input diameters ranging from 400 to 5000 μm. The output from the lens was characterized by a fiber spectrometer at three distances from the lens creating a profile of the output beam. Complementary experiments were then performed with a 532 nm laser to provide a direct comparison to the broadband source and mimic typical usage of the lens. The results show that while the resultant output does produce a line of white light, the intensity of the output is reduced when compared to the source. In addition, the input diameter of the source can be greater than specified limit of the lens, depending on the application as imperfections in the lens surface can cause aberrations in the output.

We present simulations of the scatter pattern of a 1D rough surface using a novel source with which both the coherence and polarization of the incident light can be controlled. This recently developed variable coherence polarimetry source allows the recovery of useful information of the rough surfaces, without having to scan over incidence or scatter angles. The source uses a liquid-crystal phase modulator to control the polarization as well as the coherence of the beam illuminating the rough surface. In our case we scanned two source spots over the rough surface by changing the phase distribution on the spatial light modulator. Changing the polarization state distribution at the source plane gives control of the polarization, or Stokes vector, of the light in these two spots, as well as a central static spot. The scattered beam is analyzed with a Stokes polarimeter. To simulate the experimental results, the Kirchhoff approximation is used to calculate the scattered Stokes vector using the experimental incident Stokes vector and intensity distribution as a source. It is shown that the material of the rough surface can be obtained from the measured scattered light, as well as an estimation of the average surface slope.

Gemstone identification and evaluation for jewelry pieces are limited by the interference from the surrounding metal mount and adjacent gemstones. To maintain transparency in the jewelry market, here we propose an imaging-assisted scanning Raman/photoluminescence(PL) spectroscopy for mounted gemstone measurement. The system can automatically align and measure multiple gemstones samples on a jewelry piece sequentially. The experimental prototype demonstrates capability of noninvasively measurement for separating natural diamond from its lab-grown counterparts and diamond simulants, identifying popular color gemstones, and using the color image for gemstone color evaluation and weight estimation.

We present our results on the development of a technique for the detection of dilute atomic beams by cavity ring-down spectroscopy (CRDS). These measurements were realized with an external cavity diode laser targeting the erbium 400.9 nm transition and a customized ring-down cavity under vacuum. Collimated atomic beams of different number densities were generated by controlling the temperature of a tantalum foil micro-crucible. Absorption values between 3×10-6 and 7×10^-6 were measured with a precision on the order of 10^-6. Number densities of erbium atoms were inferred to be between 2 – 4 × 10⁶ cm^-3. This work demonstrates for the first time the capability of studying dilute atomic beams of refractory materials with high accuracy utilizing CRDS. The proposed approach can be extended to the measurement of other refractory elements, such as the actinides.

Image mapping spectrometer (IMS) allows to obtain 3D (x,y,λ) datacubes instantaneously in a snapshot mode. It has a wide range of applications, including cell signaling, cancer diagnostics, and retinal imaging. The key component, multifaceted mapping mirrors, were fabricated by diamond machining, which have issues causing the variant intensity of facets and limited spatial samplings. Here we present an entirely new fabrication technique using lithographic Two-Photon Polymerization (2PP). A pixelized mapping mirror with an aluminum coating was designed and fabricated to overcome the challenges brought by prior mapping mirrors. A prototype IMS was set up on the bench to show preliminary fluorescence hyperspectral images.

Cardiomyocyte Ca²⁺ overload is known to disrupt cardiac excitation/conduction; however, unknown is how large area of Ca²⁺-overloaded myocardium is required to provoke such abnormalities. We sought to visualize patterns of excitation/conduction in a cardiomyocyte monolayer before and after localized flash photolysis of caged Ca²⁺. Under electrical stimulation at 2-5 Hz and Fluo8 fluorescence imaging, the monolayer exhibited spatiotemporally uniform propagation of Ca²⁺ transients. Upon UV-light flash (365nm, 70mW/cm^2, 20-250mm^2) the monolayer exhibited increases in Ca²⁺-transient amplitude with occasional emergence of automatic excitation and/or conduction delay on the flashed area. This experimental approach may provide deeper insights into understanding cardiac arrhythmias.

The goal of this paper is to show development and research as well as building and testing a of novel UV-C disinfection device prototype for small surfaces in public transportation. Device prototype has been successfully developed and tested on S. aureus and E. coli bacteria and could be modified to suite various other applications in public spaces. After testing, there is still room for improvement and authors have given their fair thoughts of how to achieve better results.

Photothermal ablation of biological tissue is a powerful minimally invasive technique capable of selectively destroying high-risk localized lesions using near infrared laser light delivered through thin optical fibers. As such, photothermal therapy (PTT) holds great therapeutic potential particularly in the context of cancer treatment, however, effective implementation has proven challenging due to lack of availability of direct treatment monitoring. Currently, MRI is the modality of choice due to molecular contrast and thermometry capability, unfortunately slow imaging speed as well as high cost and complexity are significant impediments preventing widespread adoption. Photoacoustic imaging (PAI) can in principle overcome these limitations since it provides multispectral molecular contrast and thermometry, while easily implemented at video frame rates. Nevertheless, current embodiments of PAI systems have failed to provide sufficient imaging sensitivity to changes in tissue temperature and optical properties during PTT at clinically relevant scales. We are developing a PTT-specific PAI system with specialized detectors capable of visualizing bulk-tissue optical property changes, as well as temperature, at imaging scales of up to several cm. We show that, despite the traditional interpretation, photoacoustic signals are not limited to depending on only the optical absorption coefficient but can be influenced by temperature. Finally, by combining PTT with novel organic nanoparticles (Porphysomes) and diffuse optical tomography, both developed at our center, we demonstrate theranostic potential through enhanced lesion localization and thermal confinement. These developments have significant implications for guiding minimally invasive photothermal treatments with reduced or eliminated collateral tissue damage and consequently preservation of posttreatment quality of life.

The angular spectrum method solves the vector Helmholtz equation for describing the propagation of the electric field rigorously. We present how the decomposition of the vector field by implementing intrinsic coordinates renders the propagation formulas analytically attractive by formulating analytical solutions for the propagated field. We investigate the validity range of different methods to calculate the projected focal spot: brute force integration, scalar angular spectrum decomposition and paraxial approximation. We combine our approach with the chirp Z transform to further extend the applicability range of the angular spectrum method and enable fine sampling of the focal spot beyond the limits of the fast fourier transform. The method can be applied to study focusing of highly converging light from aplanatic metalenses, such as immersion lenses for microscopy.

Traditionally, inverse design technology aimed to optimize fixed-shape optical structures which were based on basic shapes such as triangles or circles. However, the increasing demand for multifunctional and high-performance metasurface has brought about a need for a freeform design method that can handle a large design space with a magnitude of several orders higher than traditional structures. Here, we formulate the design problem of a beam deflector made of one-dimensional freeform silicon metasurface as a Reinforcement Learning (RL) problem. By utilizing RL, without a need for any prior metasurface data, we show that the suggested algorithm can derive optimal structures of the given problem with a simple neural network structure. During training, an agent designed as a deep Q-network randomly explores the design space and exploits its knowledge to optimize the deflection efficiency. The design strategy showed overall improvements in maximum efficiency when compared to state-of-the-art baseline approaches. Also, the algorithm proved its robustness by showing a small variance for multiple experimental initializations.

In the past two decades, solid-state lighting has steadily expanded to outperform many traditional lighting technologies due to its higher energy efficiency, longer lifetime, and reduced maintenance. The effectiveness of a solid-state lighting design for a given application relies upon the optimum use of its sub-components. An LED lighting system uses an optical subsystem with secondary optics to optimize the total luminous flux on the application surface, thus increasing its application efficiency. Therefore, it is essential to use well-defined secondary optics to achieve desired illumination patterns, luminous efficiency, and lighting uniformity. Hence, this study focused on developing a 3D printable refractive lens structure that collects luminous flux from the LED light source and redirects it into the spherical lens array. Subsequently, the spherical refractive array structures are designed in the lens to redirect the accumulated luminous flux onto the target plane to increase the application efficacy and uniformity. The designed lens is later fabricated using 3D printing to perform the experimental study. The results confirm the possibility of using a refractive array lens with a backend structure to achieve higher application efficacy.

This paper describes a novel mathematical approach for correcting image distortions created with an optical laser scanning system employing a two-dimensional rotatable plane mirror. The image distortions are created by the movement of the plane mirror during the scanning process. Scanning mirror systems are frequently used in a variety of fields, such as medical imaging, material processing, device measurement, and three-dimensional scanning. The case of a fast steering scanning mirror used for low energy material retro-reflection measurements is studied. The system described suffers from distortions. This paper presents the derivation of a novel mathematical model used to correct the distortions. The corrections obtained from the model are tested and verified by application to an experimentally acquired data set.

In the SiM4diM project we improve the measurement uncertainty of bidirectional optical measurements in industrial inspection to below a tenth of a micrometer. This will be achieved by combining highly accurate focal and afocal measurements with a robust model of the measured intensity of the structure in question. The inverse problem is then efficiently solved by applying a machine learning algorithm in the form of Bayesian optimization. We present a practical guide to modelling an optical system as well as the latest results of the SiM4diM project, showcasing improved edge detection over the state of the art.

At present, solid-state light sources are more efficacious than traditional lighting technologies. To provide benefits in the target applications, this efficacy advantage at the light source has to be supplemented by the optical system used in the lighting system. In general, optical systems can be broadly classified as refractive or reflective based on the optical elements used in the lighting system. Usually, these secondary optic elements are made using injection molding (lenses) or casting and subsequent machining and polishing (reflectors) in large-scale productions. This aspect tends to reduce the use of unique or custom optical solutions in practical applications. Additive manufacturing, or 3D printing, has been successfully used to manufacture small- to medium-scale production volumes of customized solutions in other industries. This technology provides an opportunity to manufacture optical components that maximize the efficacy of a target application by creating unique optical components that facilitate the distribution of light in desired directions. In this study, an optical system based on reflective principles was designed to provide a Type V distribution on the target plane. The designed reflector system was 3D-printed and laboratory tested for total light output, intensity distribution, light output distribution, and optical efficiency. The test results were compared with Monte Carlo ray-tracing simulation results.

With LED lighting technology having matured in the past few years, lighting fixture manufacturers are now looking to add value to LED systems by introducing novel concepts through different sub-components. In conventional refractive optical systems, the lens outer surface geometries are used to shape the output beam distribution. As a result of geometries used on external surfaces, dust and dirt could accumulate on the surface of the secondary optics, decreasing the fixture’s efficiency over time. Furthermore, exterior surfaces with complex geometries are difficult to clean and maintain. Hence, this study is focused on developing a 3D printable lens with planar exterior surfaces and internal cavity structures for beam shaping. The authors investigated the feasibility of using internal cavity structures with refractive spherical arrays to achieve prescribed illuminance distribution. The lens design strategy contains an iterative optimization procedure on internal cavity parameters to improve optical efficiency. Also, the study suggests that 3D printing can be used to manufacture internal cavity structures that are challenging to create using conventional methods.

This paper presents a technical ensemble between a mobile projector and smartphone camera for providing colorimetrically calibrated realistic experience everywhere. Since portable projectors can be used in any places without a dedicated white screen, it is very essential to calibrate color of output videos no matter what a colored surface is used for a screen. That is, a calibration process is strongly required to realize the constant intended color experience while using mobile projectors. For that, we build an easy calibration process as follows. First, the (Android or iOS) mobile and projector are connected in a common local common network, and then a mobile application generates a specific electro-optical (RGB-XYZ) conversion function by capturing re ected light from a given specific white plate. The smartphone that plays the role of an optical measurement device transmits measured light information and calibration instruction to the display system. Then the projector adjusts its light outputs and notify the status to the mobile. This `measurement-adjustment' process is recursively conducted within few seconds. The process is completed when the adjustment result meets a stop condition for a calibration target on given colored wall screen. Based on our experimental results of photometric calibration using many kinds of recently released Android and iOS smartphones, the e effectiveness of the methods is proven.

Light field visualization technology offers a glasses-free 3D experience that may be enjoyed by multiple observers simultaneously. The overall visual experience depends on a multitude of factors, among which is light ray density. In case of horizontal-only parallax displays, it defines the smoothness of the horizontal motion parallax, which is crucial to visualization quality. However, the perceived light ray density naturally depends on the viewing distance; the farther the observer is, the fewer light rays may address the two pupils, with respect to a single point on the screen. Research on this topic has already been initiated and the first results are now available in the scientific literature. However, the experiment, similarly to the vast majority of research efforts regarding the perceived quality of light field visualization, is built on the participation of individuals that are screened for normal vision. Yet a notable portion of potential future users would not pass such screening, particularly the Snellen chart on visual acuity. In this paper, we investigate the suitability of viewing distances for the future use cases of light field visualization from the perspective of users with reduced visual capabilities. The subjective tests evaluate contexts of passive visual consumption, such as a cinematic experience or an exhibition of cultural heritage. The selected use cases are not only assessed by their natural viewing distance intervals, but by closer and farther distances as well. The output of the research aims to extend the social inclusion of potential systems and services of light field visualization.

High Dynamic Range (HDR) imaging has proven its importance in numerous applications over the recent years. In the industry, there is an evident strive to further enhance the quality of the captured contents. Accordingly, legacy Low Dynamic Range (LDR) images are currently being reconstructed as HDR images due to their importance and usage in so many use case contexts. Analogous to conventional LDR and HDR images, the HDR reconstruction of light field images has also become relevant within the scientific community. Although the procedure of reconstruction is similar in several ways, the creation of HDR light field contents poses a significantly greater challenge and suffers from obstacles that are not present in case of the 2D counterpart. In this paper, we provide a context-dependent analysis of HDR light field imaging. The investigated use cases include, but are not limited to industrial prototyping, medical applications, control systems, digital signage, exhibitions of cultural heritage, education, cinematography and communication. The work takes into consideration global illumination and rendering challenges. The topics of real-time systems and services, cost-efficient practices, content availability, baseline-specific considerations, apparatus-specific optical limitations, user interaction and general plausibility are additionally emphasized in the analysis. The paper also provides a set of recommendations regarding the use-case-specific requirements of the investigated practical contexts.

Ultraviolet-visible (UV-Vis) absorption spectroscopy has been widely exploited by the gemstone industry, as it can be used to identify natural and synthetic gemstones, type of gemstone, and the origin of their color, all using a non-destructive method. Current spectrometers for gemstone identification capture required spectral information, however, they have a few noticeable disadvantages: it is difficult to customize the setup (adding fluorescence/LED illumination, implementing new software functions to capture time series data etc.), they can have long measurement times, and high maintenance cost. Due to these reasons, we have designed a UV-Vis absorption spectrometer that can capture spectra from 220 nm to 990 nm, with a measurement time up to 10 seconds. The device can be used to measure both loose/mounted gemstones, with almost no sample size limitation. They have been installed globally for diamonds, colored stones and pearl production. Several new options are currently being developed for the current unit: new software functions such as time series spectra measurements and hardware updates specifically for diamond treatments and coating detection. Besides the UV-Vis wavelength range, a new approach is to further extend the current wavelength range (up to 990 nm) to the Near-Infrared (NIR) – Mid-Infrared (MIR) range (up to 5μm). Spectrometers based on up-conversion phenomenon of non-linear crystal have been utilized for this research. The target for this development is towards quick and easy operated gemstone screening.

The efficient technique based on the Bouguer-Lambert-Beer law for experimental measurement of the concentration value of an optically scattering medium is presented. The software for batch analysis of intensity distributions of scattered laser beam is developed and tested. An experimental laboratory setup to measure the concentration value of a scattering suspension of polystyrene microbeads is assembled.

We report the design of a modified angular diversity receiver (ADR) with reduced size and improved communication performance for indoor VLC applications. The proposed design has four freeform and one spherical lens mounted on five co-planer photodiodes. An extended polynomial surface is used to determine the slope of the freeform lens with a quadrilateral off-axis field of view (FoV) (28° × 28°). Four identically designed freeform lenses are placed in a 2×2 format keeping 90° angular separation. Due to the orthogonal slope alignment of the proposed structure, the angular diversity is established. The distinct off-axis FoV of the freeform lenses introduce an uncorrelated channel gain in a multiple-input multiple-output (MIMO) VLC framework. A spherical lens with a narrow FoV (~15°) is also placed at the middle of quadrupole freeform lenses to ensure high SINR of 156 dB when the receiver approaches to the nadir of any transmitter. The compact physical dimension of the designed receiver structure (11.2 mm × 11.2 mm × 6.1 mm) is highly advantageous to facilitate VLC at any handheld gadget. Considering a square indoor environment (5m × 5m × 3m), an excellent average SINR performance of 95.7 dB is observed over the communication floor.