Showing papers in "Optical Engineering in 2020"
TL;DR: Fiber Bragg grating has embraced the area of fiber optics since the early days of its discovery, and most fiber optic sensor systems today make use of fiber Bragg-grating technology as discussed by the authors.
Abstract: Fiber Bragg grating has embraced the area of fiber optics since the early days of its discovery, and most fiber optic sensor systems today make use of fiber Bragg grating technology Researchers have gained enormous attention in the field of fiber Bragg grating (FBG)-based sensing due to its inherent advantages, such as small size, fast response, distributed sensing, and immunity to the electromagnetic field Fiber Bragg grating technology is popularly used in measurements of various physical parameters, such as pressure, temperature, and strain for civil engineering, industrial engineering, military, maritime, and aerospace applications Nowadays, strong emphasis is given to structure health monitoring of various engineering and civil structures, which can be easily achieved with FBG-based sensors Depending on the type of grating, FBG can be uniform, long, chirped, tilted or phase shifted having periodic perturbation of refractive index inside core of the optical fiber Basic fundamentals of FBG and recent progress of fiber Bragg grating-based sensors used in various applications for temperature, pressure, liquid level, strain, and refractive index sensing have been reviewed A major problem of temperature cross sensitivity that occurs in FBG-based sensing requires temperature compensation technique that has also been discussed in this paper
163 citations
TL;DR: In this paper, a range of flexible and rigid organic light emitting diodes (OLEDs) were compared with inorganic LEDs in terms of power-current and radiation patterns.
Abstract: In recent years, we have seen an increased use of organic light emitting diodes (OLEDs) for illumination in indoor environments due to the softer light compared with the conventional inorganic LEDs. In addition, OLEDs have been reported in visible light communication (VLC) systems, specifically for applications with lower data rates such as information boards, camera communications and positioning. However, OLEDs need extensive electrical and optical characterization if they are going to be fully exploited in VLC. This paper investigates characteristics of a range of flexible and rigid OLEDs and compares them with inorganic LEDs. We show that, OLEDs have highly linear power-current characteristics, and compared with rigid OLEDs with beam patterns closely matching Lambertian profile, the flexible OLED's radiation pattern is wider than Lambertian. Based on the measured experimental data, a new expression for the OLED's beam pattern, which follows the 3-term Gaussian profile, is proposed. Moreover, we show that using larger size OLED in VLC links offers improved bit error rate performance over a wide tilting angle up to 80° and a transmission path length up to 60 cm.
98 citations
TL;DR: This survey focuses on different hyperspectral image compression algorithms that have been classified into two broad categories based on eight internal and six external parameters and identified research challenges and suggested future scope for each technique.
Abstract: Rapid advancement in the development of hyperspectral image analysis techniques has led to specialized hyperspectral missions. It results in the bulk transmission of hyperspectral images from sensors to analysis centers and finally to data centers. Storage of these large size images is a critical issue that is handled by compression techniques. This survey focuses on different hyperspectral image compression algorithms that have been classified into two broad categories based on eight internal and six external parameters. In addition, we identified research challenges and suggested future scope for each technique. The detailed classification used in this paper can categorize other compression algorithms and may help in selecting research objectives.
47 citations
TL;DR: Flexible devices presented here satisfy the functionality of NAND (NOT-AND), NOR (not-OR), and XNOR (exclusive NOR) logic gates using only one structure with proper changes in the phase of an applied light signal.
Abstract: All-optical photonic integrated devices have gained great attention in the field of optical computing and large-scale integration. All-optical logic gates are useful for optical signal processing and optical communication network. The flexible devices presented here satisfy the functionality of NAND (NOT-AND), NOR (NOT-OR), and XNOR (exclusive NOR) logic gates using only one structure with proper changes in the phase of an applied light signal. The design of all-optical logic gates is implemented with photonic crystal waveguides using square lattice silicon rods. The performance of the structure is simulated, verified, and analyzed by the finite-difference time-domain method, with the principle of interference effect at a wavelength of 1550 nm. The contrast ratio (CR) of NAND, NOR, and XNOR logic gates is 17.59, 14.3, and 10.52 dB, respectively, with an optimized size of 7.2 μm × 5.4 μm.
45 citations
TL;DR: In this article, a novel Zeonex-based photonic crystal fiber (PCF) with a honeycomb-like cladding structure and a hexagonal slotted core is proposed.
Abstract: A novel Zeonex-based photonic crystal fiber (PCF) with a honeycomb-like cladding structure and a hexagonal slotted core is proposed. The finite-element method is used to numerically analyze the guiding characteristics of the proposed fiber. The investigations are carried out by optimizing various geometrical parameters of the fiber and varying the frequency, core diameter, and core porosity. The results indicate that the designed PCF demonstrates an ultrahigh birefringence of 0.083, extremely low confinement and effective material loss of 10 − 8 and 0.095 cm − 1, respectively, and a very high core power fraction of 52.2% at an operating frequency of 1.5 THz. In addition, other guiding properties such as numerical aperture, dispersion, and effective area are also analyzed and discussed in detail. The obtained results show that the proposed PCF is extremely suitable for use in numerous low-loss, polarization-maintaining applications in the terahertz frequency range.
27 citations
TL;DR: A deep multimodal image fusion (DIF) framework is proposed to detect the target by fusing the complementary information from multi-modal images with a deep convolutional neural network.
Abstract: Automated situation awareness (ASA) in a complex and dynamic setting is a challenging task. The accurate perception of environmental elements and events is critical for the successful completion of a mission. The key technology to implement ASA is target detection. However, in most situations, targets of interest that are at a distance are hard to identify due to the small size, complex background, and poor illumination conditions. Thus, multimodal (e.g., visible and thermal) imaging and fusion techniques are adopted to enhance the capability for situation awareness. A deep multimodal image fusion (DIF) framework is proposed to detect the target by fusing the complementary information from multimodal images with a deep convolutional neural network. The DIF is built and validated with the Military Sensing Information Analysis Center dataset. Extensive experiments were carried out to demonstrate the effectiveness and superiority of the proposed method in terms of both detection accuracy and computational efficiency.
27 citations
TL;DR: In this paper, a boundary elements method is used as a rigorous scattering model to calculate the scattered field at a distant boundary, and the optical response of a CSI system can be predicted for almost any arbitrary surface geometry.
Abstract: Coherence scanning interferometry (CSI), a type of interference microscopy, has found broad applications in the advanced manufacturing industry, providing high-accuracy surface topography measurement. Enhancement of the metrological capability of CSI for complex surfaces, such as those featuring high slopes and spatial frequencies and high aspect-ratio structures, requires advances in modeling of CSI. However, current linear CSI models relying on approximate surface scattering models cannot accurately predict the instrument response for surfaces with complex geometries that cause multiple scattering. A boundary elements method is used as a rigorous scattering model to calculate the scattered field at a distant boundary. Then, the CSI signal is calculated by considering the holographic recording and reconstruction of the scattered field. Through this approach, the optical response of a CSI system can be predicted for almost any arbitrary surface geometry.
26 citations
TL;DR: In this article, the authors review and discuss the problems existing in the adaptive control of laser-directed energy deposition (LDED) and propose an effective and potential way to solve the problem.
Abstract: Laser directed energy deposition (LDED) is one of the most important parts of metal additive manufacturing, which can provide fast building speed, allows for large building volumes, and is suitable for part repair. LDED can manufacture components layer by layer through processes of rapid heating, melting, solidification, and cooling with the laser beam as a heat source. However, deposition quality and repeatability of components produced by LDED are poor because of the complex thermal cycle and processing environment, hindering the spread of this technique. Adaptive control technology (ACT) is consistently considered an effective and potential way to solve the problem. Many studies have focused on LDED and established the relations of process parameters, process signatures, and product qualities, which promote the rapid development of ACT, with the development of monitoring devices and data processing technology. We review and discuss the problems existing in the ACT of LDED.
22 citations
TL;DR: In this paper, an ultrawideband (UWB) antenna covering the lower terahertz band is designed and numerically analyzed, and the antenna response can be set with the tunable single/dual/triple band-notch characteristics depending on the size and location of the applied graphene nanoribbons.
Abstract: An ultrawideband (UWB) antenna covering the lower terahertz band is designed and numerically analyzed. A number of higher-order modes are excited and merged to provide the UWB response. The band-notch is obtained by applying graphene nanoribbons at the top of the radiating metallic patch. The antenna response can be set with the tunable single/dual/triple band-notch characteristics depending on the size and location of the applied graphene nanoribbons. The notched frequency band can be tuned by changing the chemical potential of the graphene nanoribbons by keeping the cutoff frequencies of the antenna response unchanged. Moreover, the antenna radiates like a monopole throughout the passband with consistent radiation pattern, high gain, and radiation efficiency.
22 citations
TL;DR: In this paper, the authors review progress in forming ChG-based gradient refractive index (GRIN) materials from diverse processing methodologies, including solution-derived ChG layers, poled ChGs with gradient compositional and surface reactivity behavior, nanocomposite bulk ChGs and glass ceramics, and metalens structures realized through multiphoton lithography.
Abstract: Optical materials capable of advanced functionality in the infrared will enable optical designs that can offer lightweight or small footprint solutions in both planar and bulk optical systems. The University of Central Florida’s Glass Processing and Characterization Laboratory, together with our collaborators, have been evaluating compositional design and processing protocols for both bulk and film strategies employing multicomponent chalcogenide glasses (ChGs). These materials can be processed with broad compositional flexibility that allows tailoring of their transmission window, physical and optical properties, which allows them to be engineered for compatibility with other homogeneous amorphous or crystalline optical components. We review progress in forming ChG-based gradient refractive index (GRIN) materials from diverse processing methodologies, including solution-derived ChG layers, poled ChGs with gradient compositional and surface reactivity behavior, nanocomposite bulk ChGs and glass ceramics, and metalens structures realized through multiphoton lithography. We discussed current design and metrology tools that lend critical information to material design efforts to realize next-generation IR GRIN media for bulk or film applications.
22 citations
TL;DR: In this article, wave-optics simulations were used to look at the Monte Carlo averages associated with turbulence and steady-state thermal blooming (SSTB), and the results showed that the log-amplitude variance and branch-point density increase significantly due to TTBI.
Abstract: Part I of this two-part paper uses wave-optics simulations to look at the Monte Carlo averages associated with turbulence and steady-state thermal blooming (SSTB). The goal is to investigate turbulence thermal blooming interaction (TTBI). At wavelengths near 1 μm, TTBI increases the amount of constructive and destructive interference (i.e., scintillation) that results from high-power laser beam propagation through distributed-volume atmospheric aberrations. As a result, we use the spherical-wave Rytov number and the distortion number to gauge the strength of the simulated turbulence and SSTB. These parameters simplify greatly given propagation paths with constant atmospheric conditions. In addition, we use the log-amplitude variance and the branch-point density to quantify the effects of TTBI. These metrics result from a point-source beacon being backpropagated from the target plane to the source plane through the simulated turbulence and SSTB. Overall, the results show that the log-amplitude variance and branch-point density increase significantly due to TTBI. This outcome poses a major problem for beam-control systems that perform phase compensation.
TL;DR: In this article, the photogating effect was induced by photosensitizers situated around a graphene channel that coupled incident light and generated a large electrical charge, and the results obtained in this paper will contribute to the development of high-performance graphene-based IR imaging sensors.
Abstract: We demonstrated a middle-wavelength infrared (MWIR) graphene photodetector using the photogating effect. This effect was induced by photosensitizers situated around a graphene channel that coupled incident light and generated a large electrical charge. The graphene-based MWIR photodetector consisted of a top graphene channel, source–drain electrodes, an insulator layer, and a photosensitizer, and its photoresponse characteristics were determined by current measurements. Irradiation of the graphene channel of the vacuum cooled device by an MWIR laser generated a clear photoresponse, as evidenced by modulation of the output current during irradiation. The MWIR photoresponse with the photogating effect was 100 times greater than that obtained from conventional graphene photodetectors without the photogating effect. The device maintained its MWIR photoresponse at temperatures up to 150 K. The effect of the graphene channel size on the responsivity was evaluated to assess the feasibility of reducing the photodetector area, and decreasing the channel area from 100 to 25 μm2 improved the responsivity from 61.7 to 321.0 AW − 1. The results obtained in our study will contribute to the development of high-performance graphene-based IR imaging sensors.
TL;DR: In this article, an in situ calibration method based on digital holography is proposed to calibrate the spatial nonuniformity of phase modulation of the SLM panel, where the differential phase on hundreds of blocks can be reconstructed through holograms.
Abstract: Reliable phase-only spatial light modulators (SLMs) are in demand for accurate phase modulation in a wide range of fields. Due to the nonlinear optical response of liquid crystals and the limited manufacturing process available, the spatial nonuniformity of the phase modulation by the pixels should be measured and/or calibrated. We propose an in situ calibration method based on digital holography to calibrate the spatial nonuniformity of phase modulation of the SLM. The SLM panel is divided into blocks composed of pixels. The differential phase on hundreds of blocks can be reconstructed through the holograms. The distribution of modulated phase can then be derived after eliminating statics phase anomalies. The spatial nonuniformity of the panel can be measured for calibration with high efficiency. A modulated phase step on the SLM was calibrated to increase linearly. The spatial nonuniformity was calibrated to decrease by more than 75% using only a beam splitter and an imaging sensor. The in situ strategy for low cost and efficient calibration was demonstrated with optical experiments using a 4K (3840 × 2160 pixels) phase-only SLM.
TL;DR: In this article, wave-optics simulations were used to look at the Monte Carlo averages associated with turbulence and time-dependent thermal blooming (TDTB), and the results showed that the log-amplitude variance and branch-point density increase significantly due to TTBI.
Abstract: Part II of this two-part paper uses wave-optics simulations to look at the Monte Carlo averages associated with turbulence and time-dependent thermal blooming (TDTB). The goal is to investigate turbulence thermal blooming interaction (TTBI). At wavelengths near 1 μm, TTBI increases the amount of constructive and destructive interference (i.e., scintillation) that results from high-power laser beam propagation through distributed-volume atmospheric aberrations. As a result, we use the spherical-wave Rytov number, the number of wind-clearing periods, and the distortion number to gauge the strength of the simulated turbulence and TDTB. These parameters simply greatly given propagation paths with constant atmospheric conditions. In addition, we use the log-amplitude variance and the branch-point density to quantify the effects of TTBI. These metrics result from a point-source beacon being backpropagated from the target plane to the source plane through the simulated turbulence and TDTB. Overall, the results show that the log-amplitude variance and branch-point density increase significantly due to TTBI. This outcome poses a major problem for beam-control systems that perform phase compensation.
TL;DR: An underwater image enhancement framework for autonomous underwater vehicles platform is proposed, which consists of underwater light source optimization and illumination nonuniformity correction and an adaptive filter-based illumination correction algorithm to solve the uneven illumination caused by the artificial light source.
Abstract: Underwater imaging has been increasingly employed in vision-based marine research. However, the inappropriate installation of a light source and the complex underwater environment will result in the uneven illumination and overexposure on the captured images. To address these issues, an underwater image enhancement framework for autonomous underwater vehicles platform is proposed, which consists of underwater light source optimization and illumination nonuniformity correction. The light source optimization method improves the imaging quality by computing an appropriate angle of the light casting. In this way, the center of the field of view is always well lit. In addition, an adaptive filter-based illumination correction algorithm is proposed to solve the uneven illumination caused by the artificial light source. During this process, image block segmentation and the measure of image enhancement index are applied to improve the adaptability and reduce the calculation errors of the filter parameters. A dataset with real underwater images collected under different natural conditions has been built and tested. The experimental results indicate that the proposed method is more adaptive and effective than the typical methods.
TL;DR: This work aims to address limitations and present a comprehensive review of CGH-related hardware implementations and provide performance comparisons between different architectures for the evaluation of the suitability of recent hardware platforms for CGH algorithms.
Abstract: Computer-generated holography (CGH) is a technique to generate holographic interference patterns. One of the major issues related to computer hologram generation is the massive computational power required. Hardware accelerators are used to accelerate this process. Previous publications targeting hardware platforms lack performance comparisons between different architectures and do not provide enough information for the evaluation of the suitability of recent hardware platforms for CGH algorithms. We aim to address these limitations and present a comprehensive review of CGH-related hardware implementations.
TL;DR: In this paper, an active hyperspectral image (HSI) cube is generated by sweeping the wavelength of the IR quantum cascade laser while collecting image frames with the FPA, and the HSI cube contains both spatial and spectral information, where the spectrum of a pixel or region of interest within the image can be extracted and compared against a known threat library.
Abstract: We are using active infrared (IR) spectroscopic imaging to detect trace explosives on surfaces at proximal distances up to a few meters. The technology comprises an IR quantum cascade laser (QCL) for illumination and an IR focal plane array (FPA) sensor to collect signal backscattered from surfaces of interest. By sweeping the wavelength of the QCL while collecting image frames with the FPA, we generate an active hyperspectral image (HSI) cube. The HSI cube contains both spatial and spectral information, where the spectrum of a pixel, or region of interest within the image, can be extracted and compared against a known threat library. These cubes are fed into a convolutional neural network (CNN) trained on purely synthetic data to identify chemicals in the field of view. The CNN identifies chemicals by their IR signature and identifies their location within the image.
TL;DR: In this article, a terahertz imaging system consisting of an impact avalanche and transit time-diode source, a condenser lens, and an imaging camera was used to monitor the hydration state of plants in their natural environment.
Abstract: Quantitative analysis of the temporal evolution and spatial distribution of water content in grass and clover leaves has been carried out in vivo , with the aid of the terahertz imaging system comprised of an impact avalanche and transit time-diode source, a condenser lens, and an imaging camera. The leaf samples were exposed to 100-GHz radiation to measure the transmitted power. Progressive variation in the level of the transmitted signal has been detected when the plants were subject to the condition of insufficient water supply, whereas after watering the plants, the transmission was restored to its initial value. The presented experimental results demonstrate that TeraSense imaging instrumentation can be effectively used to monitor the hydration state of plants in their natural environment.
TL;DR: In this paper, the photoresponse mechanism of a graphene/InSb heterojunction middle-wavelength infrared (MWIR) photodetectors was investigated.
Abstract: The photoresponse mechanism of graphene/InSb heterojunction middle-wavelength infrared (MWIR) photodetectors was investigated. The devices comprised a graphene/InSb heterojunction as a carrier-injection region and an insulator region of graphene on tetraethyl orthosilicate (TEOS) for photogating. The MWIR photoresponse was significantly amplified with an increase in the graphene/TEOS cross-sectional area by covering the entire detector with graphene. The graphene-channel dependence of the MWIR photoresponse indicated that the graphene carrier density was modulated by photocarrier accumulation at the TEOS/InSb boundary, resulting in photogating. The dark current of the devices was suppressed by a decrease in the graphene/InSb carrier-injection region and the formation of the heterojunction using an n-type InSb substrate. The results indicate that photocarrier transportation was dominated by the formation of a Schottky barrier at the interface of the graphene/InSb heterojunction and a Fermi-level shift under bias application. The high-responsivity and low-dark-current photoresponse mechanism was attributed to the graphene/InSb heterojunction diode behavior and the photogating effect. The devices combining the aforementioned features had a noise equivalent power of 0.43 pW / Hz1/2. The results obtained in our study will contribute to the development of high-performance graphene-based IR image sensors.
TL;DR: In this article, a metamaterial absorber-based microwave imaging detector that is operating in industrial, scientific, and medical (ISM) band is presented, which has almost perfect absorption at 2.39 GHz in simulation and 2.51 GHz in the experimental measurement.
Abstract: Our paper presents the design, fabrication, and characterization of metamaterial absorber-based microwave imaging detector that is operating in industrial, scientific, and medical (ISM) band. The results reveal that the structure has almost perfect absorption at 2.39 GHz in the simulation and 2.51 GHz in the experimental measurement. For energy-harvesting applications, Schottky diodes have been used and 11.8-mV dc voltage across a Schottky diode has been observed with 84.2% dc conversion efficiency in harvesting application. To show the different incident angle imaging, MATS-1000 antenna training kit is used, and different imaging pictures are given, which are obtained by MATLAB with the help of a microcontroller card. Both experimental and simulation study results verify that the microwave detector generates accurate images with negligible distortions. The innovative side of this study when it is compared with similar studies can be sorted as having more dc obtained voltage, incident angle characterization, and operation frequency. Simulated and measurement results show that the proposed structure can effectively be used in the imaging at ISM frequency band, which is the most common frequency band in wireless appliances.
TL;DR: In this article, the authors reviewed the advances of terahertz (THz) science and technology in biophotonics, including related challenges and solutions, and concluded that the main impediment to THz spectroscopy and imaging in this field is the high absorption of the THz beam in water.
Abstract: We review the advances of terahertz (THz) science and technology in biophotonics, including related challenges and solutions. The main impediment to THz spectroscopy and imaging in this field is the high absorption of the THz beam in water. Hence, transmission imaging and spectroscopy of thick wet tissue using THz radiation has generally been quite difficult. However, the absorption of THz waves by water molecules is so strong that increasing the power of the THz source can lead to structural and functional changes in tissues, so solutions must go beyond a larger power output. In terms of resolution, THz imaging is superior to ultrasound but inferior to visible light microscopy. Owing to its unique material analysis capabilities, promising diagnosis applications have been demonstrated through THz imaging and spectroscopy. Unfortunately, many applications are limited by beam penetration depth and resolution. Hence, researchers from a wide variety of scientific and technical fields have been actively improving these features through the development of electronic devices and materials. In addition, groundbreaking optical architecture and materials to reduce beam absorption in the optics of a system and generate focused beams with smaller diameters have been proposed. On the software side, image processing techniques to computationally enhance the resolution and quality of THz imaging have been proposed. Data science and machine learning to automate the diagnosis of defects and diseases through processing THz images and spectroscopy data have been proposed. We have reviewed the applications of THz radiation in biophotonics and research achievements toward advancing these applications. A conclusion with a roadmap toward increasing the footprint of the THz technology in biophotonics is also proposed.
TL;DR: An analytical framework for a dual-hop amplify-and-forward UV NLOS cooperative relay is developed and the closed-form expressions of lower-bound outage probability and the average symbol error rate for the energy efficient modulation schemes, such as hexagonal quadrature amplitude modulation (QAM) and rectangular QAM schemes are derived.
Abstract: Nonline-of-sight (NLOS) ultraviolet (UV) communication is expected to play a prominent role in wireless communications with enhanced connectivity due to the aerosol and strong molecular scattering and availability of large unlicensed bandwidth. We investigate the performance of NLOS UV co-operative communication over a log-normal fading channel by considering the channel estimation error, as experienced in practical UV communication systems. An analytical framework for a dual-hop amplify-and-forward UV NLOS cooperative relay is developed. We derive the closed-form expressions of lower-bound outage probability and the average symbol error rate for the energy efficient modulation schemes, such as hexagonal quadrature amplitude modulation (QAM) and rectangular QAM schemes. The derived analytical results are validated through the Monte Carlo simulations.
TL;DR: This work presents a propagation-free method for simulating imaging through turbulence with applications in ground-to-ground imaging, and proposes fast and scalable sampling strategies to draw intermodal and spatially correlated Zernike coefficients.
Abstract: Simulating atmospheric turbulence is an essential task for evaluating turbulence mitigation algorithms and training learning-based methods. Advanced numerical simulators for atmospheric turbulence are available, but they require evaluating wave propagation, which is computationally expensive. We present a propagation-free method for simulating imaging through turbulence with applications in ground-to-ground imaging. The key idea behind our work is a method to draw intermodal and spatially correlated Zernike coefficients. By establishing the equivalence of the angle-of-arrival correlation by Basu, McCrae, and Fiorino (2015) with the multiaperture correlation by Chanan (1992), we show that the Zernike coefficients can be drawn according to a covariance matrix defining the correlations. We propose fast and scalable sampling strategies to draw these samples. The method allows us to compress the wave propagation problem into a sampling problem, hence making the simulator significantly faster than existing ones. Experimental results show that the simulator has an excellent match with the theory and real turbulence data. We anticipate the simulator, which balances speed and accuracy, will be a useful tool for various computational imaging applications.
TL;DR: In this paper, the effects of multiple longitudinal modes and rapid fluctuations in center frequency were simulated using sinusoidal phase modulation and linewidth broadening, respectively, and the results showed that the coherence efficiency decreases quadratically with fringe visibility.
Abstract: To simulate the effects of multiple-longitudinal modes and rapid fluctuations in center frequency, we use sinusoidal phase modulation and linewidth broadening, respectively. These effects allow us to degrade the temporal coherence of our master-oscillator laser, which we then use to conduct digital holography experiments. In turn, our results show that the coherence efficiency decreases quadratically with fringe visibility and that our measurements agree with our models to within 1.8% for sinusoidal phase modulation and 6.9% for linewidth broadening.
TL;DR: In this article, the authors demonstrate an application of digital holography for detection of a new type of defect, i.e., delamination of polyurethane pads on a polishing tool used on a high-speed computerized numerical control machine for production of precision optics.
Abstract: We demonstrate an application of digital holography for detection of a new type of defect, i.e., delamination of polyurethane pads on a polishing tool used on a high-speed computerized numerical control machine for production of precision optics. The method enabled us to acquire both qualitative and quantitative information about the delaminated region in the polishing pad. A delaminated region of 13.6 mm × 10.8 mm is detected and measured on the surface of the polishing pad. An increase in the delaminated region by 30% is noticed after completion of the polishing process with the delaminated polishing pad. The effect of delamination of the polishing pad on an optical surface is experimentally demonstrated using it for polishing a BK-7 glass substrate. These investigations may enable production of improved quality precision optics at the commercial level.
TL;DR: In this paper, an experimental system for irradiating cells with intense broadband terahertz (THz) pulses was developed to allow cells to be kept in suitable conditions for long-term exposure and to be irradiated with THz pulses in single point mode as well as in scanning mode.
Abstract: Terahertz (THz) waves can influence a diverse range of cellular processes. The use of high-power THz sources in biological studies may lead to major advances in understanding biological systems and help to determine safe exposure levels for existing THz technologies. We are devoted to the development of an experimental system for irradiating cells with intense broadband THz pulses. Subpicosecond pulses of THz radiation with intensities of 32 GW / cm2 and electric field strength up to 3.5 MV/cm are obtained by optical rectification, using an OH1 organic crystal, of near-infrared femtosecond pulses generated by a Cr:forsterite laser. The system has been developed to allow cells to be kept in suitable conditions for long-term exposure and to be irradiated with THz pulses in single-point mode as well as in scanning mode. The transmission in the THz region of various plastic dishes for cell culture is estimated.
TL;DR: In this paper, a convolutional neural network was used to identify and classify noisy images of Laguerre-Gaussian (LG) modes collected from two different experimental set ups.
Abstract: Automated detection of orbital angular momentum (OAM) can tremendously contribute to quantum optical experiments. We develop convolutional neural networks to identify and classify noisy images of Laguerre–Gaussian (LG) modes collected from two different experimental set ups. We investigate the classification performance measures of the predictive classification models for experimental conditions. The results demonstrate accuracy and specificity above 90% in classifying 16 LG modes for both experimental set ups. However, the F-score, sensitivity, and precision of the classification range from 57% to 92%, depending on the number of imperfections in the images obtained from the experiments. This research could enhance the application of OAM light in telecommunications, sensing, and high-resolution imaging systems.
TL;DR: In this article, the Monte Carlo ray trace modeling program TracePro is extended through the use of its macrolanguage to model reflectance spectra from analytes deposited on various substrates.
Abstract: Since solids are only sometimes seen en masse in a pure bulk form, and for liquids other than water almost never, a capability to model reflectance spectra from analytes deposited on various substrates would be highly advantageous. If available, the real, n ( ν ) , and imaginary, k ( ν ) , components of the complex refractive index, n∼ = n + ik, can be used to simulate infrared spectra, accounting for reflection, refraction, and absorption phenomena as a function of wavelength. We focus on using the Pacific Northwest National Laboratory (PNNL) derived n / k vectors for solid and liquid analytes deposited as thin layers on different types of substrates including conductors, such as aluminum, and inorganic dielectrics, such as glass. The model is an adaptation of the Monte Carlo ray trace modeling program, TracePro, extended through the use of its macrolanguage. The model is tested using thin films of organic liquids including silicone oil and no. 2 diesel fuel, as well as organic solids such as caffeine and acetaminophen on aluminum and glass. The predicted spectra for the solid films were compared to experimental hemispherical reflectance data measured using a Fourier transform spectrometer with an integrating sphere. The thickness of the calculated layer is a parameter for predicting the (transflectance) spectra and is obtained using the areal density measured from gravimetric methods to generate the thin-layer samples. Comparison of the calculated spectra with experimental hemispherical reflectance data shows excellent agreement, indicating promise for the use of measured n / k data to synthesize reference spectral data. In particular, accounting for the inhomogeneity of the deposits greatly improved the match with experimental data. Finally, the theoretical modeling shows that for thicker layers (ca. 20 to 100 μm) of typical organics possessing moderately strong k values, the longwave infrared features are often saturated and better spectral contrast is obtained from the overtone/combination bands in the shortwave infrared.
TL;DR: In this article, a trace chemical detector is described that combines external-cavity quantum cascade lasers and a mercury cadmium telluride camera to capture hyperspectral images of the diffuse reflectance from a target surface in the long-wave infrared.
Abstract: A trace chemical detector is described that combines external-cavity quantum cascade lasers and a mercury cadmium telluride camera to capture hyperspectral images of the diffuse reflectance from a target surface in the long-wave infrared. The system is able to generate individual hypercubes in 60 cm2 / s have been achieved. Results are presented for standoff distances ranging from 0.1 to 25 m. Hyperspectral images generated by the system are analyzed for spectral features that indicate the presence of trace surface contaminants. This approach has been found to be highly capable of detecting trace chemical residues on a wide variety of surfaces, and we present a collection of detection results to demonstrate the capabilities of this technology. Examples include the detection of 10 μg of saccharin powder on a wide range of substrates, 0.2 μg of an explosive residue on a computer keyboard, residual pharmaceuticals within a plastic baggie, and a contaminated fingerprint on cell phone case.
TL;DR: The nature of a typical camera raw space is investigated, including its gamut and reference white, and the strategy used by internal image-processing engines of traditional digital cameras is shown to be based upon color rotation matrices accompanied by raw channel multipliers.
Abstract: Color conversion matrices and chromatic adaptation transforms (CATs) are of central importance when converting a scene captured by a digital camera in the camera raw space into a color image suitable for display using an output-referred color space. In this article, the nature of a typical camera raw space is investigated, including its gamut and reference white. Various color conversion strategies that are used in practice are subsequently derived and examined. The strategy used by internal image-processing engines of traditional digital cameras is shown to be based upon color rotation matrices accompanied by raw channel multipliers, in contrast to the approach used by smartphones and commercial raw converters, which is typically based upon characterization matrices accompanied by conventional CATs. Several advantages of the approach used by traditional digital cameras are discussed. The connections with the color conversion methods of the DCRaw open-source raw converter and the Adobe digital negative converter are also examined, along with the nature of the Adobe color and forward matrices.