This PDF file contains the front matter associated with SPIE Proceedings Volume 12893, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

The Korea Astronomy and Space Science Institute (KASI) is currently developing GrainCams as a candidate payload for NASA's Commercial Lunar Payload Services (CLPS). GrainCams consists of two instruments to be mounted on a rover: LevCam, which observes levitating dust near the lunar surface, and SurfCam, designed to observe lunar regolith. Over the past two years, LevCam and SurfCam have been engaged in optical and optomechanical design work, conducting various analyses to assess manufacturability. SurfCam, being a light field camera, has seen the development of a prototype to measure initial optical performance, along with conducting preliminary assembly and alignment. Despite some minor optical specification changes this year, the overall development is still ongoing. The paper will cover SurfCam's assembly and alignment strategies and performance measurement aspects.

Stray light analysis is essential for the design of high-quality optical systems, to ensure that unwanted light reaching the sensor is minimized, and artifacts that degrade optical performance - such as lens flare – are mitigated. This article introduces a system-level approach for stray light analysis using Ansys Optics simulation tools, considering stray light from both optical and non-optical components. The article illustrates how these tools can be integrated with Ansys optiSLang for automated exploration and design optimization. The practical camera use-case highlights a seamless data exchange between Ansys Optics simulation tools. It employs a range of intuitive features, from Ansys Zemax OpticStudio's sequential ray tracing, extending to Ansys Speos ray path analysis, while leveraging HPC and Cloud Computing. The combined capabilities offer an efficient solution, streamlining collaboration and enabling optimized optical system designs.

Airborne LIDAR sensors can produce accurate 3D point clouds for terrain mapping at different altitudes. As the altitude increases, there is a need for larger aperture sizes to ensure the collection of sufficient photons and the preservation of spatial resolution. In the case of conical scanning optical systems, axially spinning refractive wedges can be used to cover a scan across the field of regard. Nevertheless, maintaining rotational balance for refractive wedges proves challenging, particularly at angles exceeding several degrees, due to their asymmetric moment of inertia. In contrast, a holographic optical element serves as an alternative scanning optic with a symmetric moment of inertia, effectively addressing stability concerns associated with substantial scan angles compared to refractive wedge-based scanners. Our study highlights that HOEs can accommodate a wide range of scan angles and aperture sizes without compromising volumetric constraints or stability, showcasing their effectiveness in optical scanning for LIDAR sensors.

Astronomy and Space Domain Awareness are limited by the size of available telescope optics, which in turn is related to the cost of exquisitely ground and polished primary mirrors. This creates the cost-size scaling “law” of optics: as the primary mirror gets larger, the cost grows polynomially, limiting mass manufacturing and proliferation. It is possible that liquid mirrors (LMs) may present a solution. When rotated at a constant angular velocity, fluid surfaces take the form of a light-focusing paraboloid with good optical quality. LMs therefore have the potential to break the cost-size scaling law and enable large-diameter optical surfaces. However, fundamental limitations remain. Traditional LMs can only point straight upward (to zenith) and are, therefore, limited in the imagery they can gather. Since the surface is a liquid, any out-of-plane movement disrupts the surface, causing spilling and rendering the imaging surface useless. Rotating machinery also adds complexity and are not scalable to very large mirror sizes. To address these limitations and enable low-cost, very-large-aperture telescopes, DARPA has launched its Zenith program. Zenith will investigate alternate LM designs and develop modeling tools, materials, surface shape controls, and structures to eliminate these limitations. The goal is to demonstrate a 2-m diameter liquid mirror telescope system (LMT) and a 1-m diameter segmented LM that require no liquid motion (rotation) to operate. Achieving Zenith goals will require unique approaches to maintaining good optical quality of a liquid surface in real time during slew and while tilted from the zenith axis. Software and simulation tools specific to liquid mirror performance modeling will be released to the astronomical community as an open-source repository at the conclusion of Phase I of the Zenith program.

We developed an ultra-precise retardation-measurement system based on optical-heterodyne interferometry with a 3σ repeatability of λ/360, 000 for zero retardation, where the frequency shift for the optical-heterodyne interferometry was generated by a rotating half-waveplate, and both polarizations for the retardation measurement were always exactly on a common path. Using this system, the direction of the c-axis of a sapphire window was determined by analyzing the incidence-angle dependence of the retardation. The possible resolution of the c-axis direction of the sapphire window was estimated to be 0.9 arcmin from the retardation-measurement repeatability. This c-axis determination method will be applicable to, for example, high-precision sapphire-mirror production/evaluation for gravitational-wave detection.

This paper presents experimental studies on heterodyne Frequency Modulated Continuous Wave (FMCW) signal reception for different optical heterodyne configurations including internal and external mixing between an incoming signal and a local oscillator. Signals and potential noise sources from a fibered FMCW Mach-Zehnder Interferometer (FMCW MZI) are theoretically evaluated. These optical estimations (signal and noise) of various power spectral densities (PSD) are converted into electrical unities to be compared to the measurements.The PSD are validated by using a known alternating voltage with controlled frequency and amplitude. This validation is used to compare the experimental and theoretical detection limits of different FMCW photodetectors, including a Photonic Integrated Circuit (PIC) detector developed and produced at CEA. The detection limit achieved with this PIC module closely matches with the expected theoretical performances. It validates the optical and electronic architecture and the achievements of CEA’s design. The miniaturization of this operational detection module is underway. In the future, it will be located on a single chip alongside two Optical Phased Arrays (OPA), one for emission and the other for reception.

The pulsed optical output of a 940-nm LD can be amplified using a current driven semiconductor optical amplifier (SOA). The pulsed light from the 940-nm LD has a pulse width of 50 ps and a repetition rate of 50 MHz, and incident on the 500-mA current driven SOA. A CW light from a 905-nm LD incident on the SOA in colinear with the pulsed light. Due to two effects of current driven amplification and optically pumped amplification, the peak power of the pulsed light was increased up to 2W and the pulse contrast was improved by a factor of 20.

Diode laser based light sources (implemented monolithically or in a hybrid configuration) offer various functionalities to meet the requirements of specific applications. This includes tuning or switching between different wavelengths, modulating the optical output power, or implemented frequency conversion. Such light sources often contain multisection diode lasers or several active elements. Their operation requires multiple individually adjustable current sources, galvanically isolated current sources, and temperature control. A suitable optical interface should be available for a subsequent integration of the turnkey into the addressed application. In this contribution, a versatile turnkey system meeting the above-mentioned requirements will be presented. Ten p-type current sources, each with currents up to 750 mA, and four galvanically decoupled current sources are implemented. The ten individual sources enable switching frequencies up to 1 kHz and can be combined to provide currents up to 7.5 A. A temperature control unit capable to remove 10 W thermal load using a Peltier element completes the system, which contains an internal microcontroller, trigger in- and outputs, and an USB interface for the integration into various environments. Moreover, fiber coupling and free space optics to transfer the laser emission are offered. Turnkey systems containing in-house developed light sources at 488 nm or 785 nm were implemented into portable Raman spectroscopic measurement systems. To separate Raman signals from background disturbances, shifted excitation Raman difference spectroscopy (SERDS) was applied using dual-wavelength light sources. Systems addressing the measurement of carotenoids under clinical conditions and soil properties in the field will be presented.

We present multi-frequency low-noise semiconductor laser sources for resonant fiber optic gyroscope (RFOG) interrogation that have enabled excellent gyro stability over temperature. Each laser source includes three distributed feedback semiconductor laser chips coupled with micro-lenses to multi-component silicon photonics (SiP) chips. A first laser, the master, is locked to the RFOG with a Pound-Drever-Hall loop. Two slave lasers are optically phase-locked to the master laser with electrical loop bandwidths of 100 MHz. The SiP chips perform beat note detection and several other functions, such as phase and intensity noise suppression. The lasers and SiP chips are packaged in an optical engine that is controlled by compact low noise electronics. The fiber pigtails are connected to the RFOG so that light is sent in clockwise and counterclockwise directions. Tracking of the RFOG resonance frequencies in both directions allows rotation sensing. An ultra-stable differential frequency noise floor of 0.05 Hz/rt-Hz was obtained between the lasers and the coil resonator which was instrumental in achieving results for the RFOG over 60˚ C operating temperature range. The corresponding angle random walk level is less than 0.01 ˚/rt-hr and was not limited by laser differential frequency noise. The gyroscope bias drift over the tested temperature range was maintained within 0.005 ˚/hr, the best-ever published RFOG performance over temperature to date.

The spectral wavelength range is expanded to 380nm - 1100nm for the laser driven light sources (LDLS) based spectral matching light source. Unlike LED-based systems, which individually adjust the output of many LEDs with various center wavelengths, the new source programmatically changes the mirror on/off pattern of a digital micromirror device (DMD) onto which the broadband LDLS light is diffracted and imaged. The LDLS-based system offers higher matching accuracy with faster switching speed due to its superior spectral resolution, higher throughput over the entire interested spectral range as well as the high switching speed of the micromirrors. The DMD’s light distribution data obtained through system characterization is fed into the matching algorithm to calculate the mirror fraction and generate the appropriate mirror pattern to match the target spectrum. Thus, the matching quality relies on whether the characterization data captures the light mapping features on the DMD both spectrally and spatially with acceptable S/N. This paper presents an automatic process to characterize the DMD’s light distribution spectrally and spatially. Then, the data will be used in the matching algorithm based on linear least square optimization with constraint to calculate the mirror fraction and generate the appropriate mirror pattern to minimize the difference between the calculated and the target spectrum. The impact of characterization configurations such as row and column pixel widths on the matching accuracy for the various types of target spectrum will be discussed.

We report on the demonstration of a laser-heated blackbody source fabricated from vertically aligned carbon nanotubes (VACNTs). This thermal source has potential use for performing micro- and nano- infrared spectroscopies because VACNTs have an extremely high melting point >3000 K, near unity emissivity across the infrared, and are compatible with lithographic microfabrication that can be exploited to maximize etendue of thermal emission.

For accurate Raman measurements, emission spectra must be free of fluorescence that obscures the critical information given by spectral “fingerprint” Raman peaks. The ideal Raman instrument can quickly and automatically generate a robust and fluorescence-free signal at the sampling point. Both mechanical and mathematical methods exist to reduce fluorescence, but with shortcomings and particular emphasis on spectral features. XTR is an algorithmic fluorescence-rejection technique that enhances the Raman spectrum for accurate analysis, identification, and verification of materials. Here, we present the fundamentals of the XTR method and provide application examples of XTR for identifying materials that have traditionally confounded Raman, like cellulose, oils, polymers, paints, and dyes.

Wave Front Phase Imaging (WFPI), a new wafer geometry technique, is presented, that acquires 16.3 million data points in 12 seconds on a full 300mm wafer, providing lateral resolution of 65μm while holding the wafer vertically. 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 free, non-gravitational wafer shape to avoid overlay errors caused by depth-of-focus issues. For a wafer shape system to perform in a high-volume manufacturing environment, repeatability is a critical measure that needs to be tested. We present WFPI as a new technique with high resolution and high data count acquired at very high-speed using a system where the wafer is free from the effects of gravity and with a very high repeatability as measured according to the Semi standards M49.

Microlens arrays (MLA) are a critical component of avalanche photodiode (APD) technology, but their performance is rarely characterized or investigated independent of the photodetector. To understand how best to improve coupling, the MLA must be characterized and compared to other technologies on a fair and consistent basis. In order to investigate new designs and compare different types of microlens technologies, a custom microscope was built. This microscope was designed to image the MLA surface as well as its focused beam which required solutions to the following challenges: 6-axis manipulation of the sample, sub-micron positional resolution, perpendicular travel to the optical axis, brightfield imaging, multispectral imaging, image processing, uniform irradiance over the sample area, and calibrated absolute optical power measurements. This microscope design enables the focal length range to be mapped with sub-micron accuracy along the paraxial ray. The imaged beam spot is quantitatively analyzed in MATLAB for 1/e² diameter and encircled energy, as well as qualitatively with complementary data sets. It was shown that Fresnel lens and plano-convex refractive MLA designs from various material groups could be compared equally in a side-by-side comparison.

This paper presents a study and development on the thermal mapping of a Three-phase Induction Motor for harsh environments application. These machines’ exceptional performance and precise speed control make them essential equipment in multiple industrial processes, such as Artificial Lift, which integrates with a multistage centrifugal pump to elevate fluids from the reservoirs to the surface. Increased motor speeds for higher production requirements can result in temperature rise, damaging the stator winding. Employing the Raman Distributed Temperature Sensing System (RDTS), we generate a comprehensive heat distribution map of the motor. ANSYS Motor-CAD was applied for computational simulations to perform steady-state thermal analysis, giving an overview of heat transfer among internal components and thermal limits for the instrumented motor. This preliminary study presents a series of experimental tests to evaluate the advantages of fiber optic temperature sensing in harsh environments, emphasizing its significance in improving electrical machines’ performance and reliability.

FTIR spectroscopy holds significant untapped potential for materials analysis and laser characterization, but new developments are limited by the availability of simple, universal, and scalable components. Addressing this challenge, pyroelectric receivers PR No1 IR and PR No2 IR, and detectors ALUT3151 with sub-pixel binning and Diff ALUT3151 with additional true differential output have been developed. All models are based on thin LiTaO₃, cover a wide wavelength range, do not require cooling, and operate at high Detectivity (D*) in the kHz range while being rugged and linear over four orders of IR flux magnitude. In this paper, we will focus on recent results towards a people´s-FTIR with reduced TTWS (Time Towards Working Setup). Besides the detector, the thermal source and the beamsplitter have been identified as critical components.

Extending the range of distributed fiber sensors is one of the major challenges in the development of offshore wind turbines in order to monitor the transmitted electrical power inside the cables. Here we report a novel technique allowing to monitor the fiber up to 140 km, with a spatial resolution of 20 m in single-ended. Our method relies on the Brillouin anti-Stokes backscattering measurements that directly depend on the temperature along the optical fiber. The actual commercial devices have a range of 75 km. As a consequence, long infrastructures can’t be monitored in single-ended. Here the proposed method allows us to monitor the temperature without the need for an amplification module.

The integration of Rayleigh and Brillouin scattering in a hybrid sensor system has revolutionized the field of distributed fiber optic sensing. This hybrid sensor system provides a strong and all-encompassing solution for monitoring multiple physical parameters, including strain, temperature, and vibrations along the sensing fiber length by combining the strengths of both scattering phenomena. We present a hybrid multi-parameter distributed sensing system in this paper that is based on the Brillouin and Rayleigh scattering mechanisms. Utilizing a single-end access to the sensing fiber, we measured acoustic vibrations based on phase-sensitive optical time domain reflectometry (Φ-OTDR), whereas we employed a Brillouin optical time reflectometry (BOTDR) for strain and temperature monitoring. The experimental results demonstrate the effectiveness of the hybrid sensor system to achieve simultaneous and independent measurements over a 25 km long single-mode silica fiber at 3 m spatial resolution. Furthermore, we used a large effective area fiber (LEAF) for simultaneous and discriminative strain, temperature, and vibration monitoring in order to get around the cross-sensitivity between the strain and temperature in the BOTDR system. A variety of applications, such as the structural health monitoring of buildings, bridges, and oil and gas pipelines, industrial process control, security, and surveillance, can be served by the suggested multi-parameter hybrid distributed sensor system.

In this paper we discuss the performance of a new generation of extended InGaAs photodetectors, the IG26H series, with a 2.6 μm wavelength cut off developed by the Laser Components Detector Group. These devices have a low leakage current over a wide range of applied reverse bias voltage and also have a high shunt resistance of 15 kOhms for 0 Volt bias applications. These photodetectors allow for the device operation up to 5 Volts reverse bias while maintaining low leakage of under 50 μAmp for a 1mm diameter active area detector thus assuring linearity of the operation of the detectors.

Next-generation mode division multiplexing (MDM) systems aim to integrate concurrent functionalities within a single optical fiber efficiently. In this work, we report on harnessing MDM to simultaneously provide data transmission and power delivery over a two-mode fiber (TMF). We deployed a 1-km TMF to convey a 1 Gbps on-off keying (OOK) data signal and deliver a 17.12 mW input optical power. Through switching the mode allocation (LP₀₁/LP₁₁ for data/power), we examined the suitability of both integrated communication and PWoF functionalities. During our analysis, we established a robust communication link with 1.933×10⁻⁵ bit error rate (BER) using the LP₁₁ mode for communication while simultaneously achieving electrical power delivery of ∼2.75 mW at the receiver side using the LP₁₀ mode. This successful integration proves the feasibility of harnessing the TMF for simultaneous data and power transmission in next-generation integrated systems/networks encompassing communication and power.

Photoelastic modulators are widely used optical instruments across many applications. Despite being in use since the 1960s, their design has remained largely unchanged. The main limitation of these modulators is the fundamental trade-off between the input aperture and the modulation frequency. These modulators typically operate around 50 kHz modulation frequency for centimeter square scale apertures. Optically isotropic and piezoelectric crystals, like gallium arsenide, gallium phosphide, zinc selenide, and zinc sulfide offer a ground-breaking opportunity to create new kinds of photoelastic modulators to overcome this trade-off. By adopting this new design, we can achieve both high modulation frequencies (in the megahertz frequency regime) and large input apertures (centimeter square scale) simultaneously.

This research introduces a new non-destructive technique for the characterization of fiber Bragg gratings (FBGs) based on the analysis of the FBG diffraction profile via measuring its asymmetry and intensity. This approach enables the determination of such FBG parameters as an off-axis displacement, aberrations of the focusing system, outcoupling efficiency of refractive index modulation, grating length, and grating order. This proposed technique can significantly improve quality control in FBG manufacturing. The applicability of this technique is demonstrated on different types of fiber Bragg gratings written by point-by-point femtosecond laser writing.

Automated Fiber Placement (AFP) is an additive manufacturing process that enables the fabrication of complex parts for the aerospace industry. In-process inspection (IPI) for AFP is a technology that has been in high demand by most manufacturers for a long time since the current quality control, based on visual inspection, is a time-consuming process. The development of an IPI system for AFP presents many challenges. We show that the Swept-Source Optical Coherence Tomography (SS-OCT) technology addresses these challenges to provide a welcomed solution to the AFP manufacturing industry.

Textile sorting for recycling and revalorisation is a multifaceted challenge that requires accurate material classification. We demonstrate the effectiveness of short-wave infrared (SWIR) hyperspectral imaging as a method employed to address this challenge. The utilization of various data processing strategies enables us to ascertain the accuracy of textile blends. Employing the Multivariate Curve Resolution-Alternating Least Square algorithm, we establish an uncertainty range of ±2.7 - 5.0% using pure elements as a training set. To achieve this, we employ multiple pre-processing methods to enhance the spectrum and assess alternative regression algorithms, such as Multivariate Regression-Partial Least Square and Principal Component Algorithm. Additionally, we conducted tests using two hyperspectral systems with distinct spectral ranges: one extending up to 2500 nm and the other up to 1700 nm. Furthermore, a study on the influence of fabric color on regression and textile spectra was conducted.

The problem in fluorescence detection of gases like ammonia over a wide range from Parts Per Millions (ppm) to 10,000’s ppm (saturation) is that often at <1000 ppm the spectra show almost no peak wavelength shift or intensity change and only subtle fluorescence spectrum alterations, so new metrics are needed. We are exploring two Vapochromic Coordination Polymers (VCP): Zn[Au(CN)₂]₂, which emits light when exposed to NH₃, shifting its peak from 470 nm to green 530 nm under high concentration while the intensity grows 3-5X. A second VCP In₂[Pt(CN)₄]₃ shifts from 560 nm (yellow) to 530 nm. To enhance spectral changes we use a 405 nm laser diode excitation source’s narrow (4nm) stimulation which is clearly separated from the spectral peak for 1000ppm. Focusing the emission on a USB portable spectrometer we enhance the subtle spectra changes with a method that gives unique all ppm values by dividing the spectrum into 10 nm bins, integrate the emission in each bin, relative to that of 0 ppm emission, then sum all the bins (Sum of Integrated Emissions, SIE). This emphasizes wavelength regions that have rapid relative changes at different ammonia ppm exposures. For Zn[Au(CN)₂]₂ VCP SIE gives excellent sensitivity between 0-100 ppm and >400 ppm, but has poor accuracy in the 100-500 ppm range. At mid ppm ranges some SIE bins decline while others increase so we switch to a second metric, Limited Range SIE, that covers only the 430-470 nm bins which show an accurate linear response. In many spectral fluorescence cases, in the region where the longer wavelength peak begins to dominate, it is best to focus on regions outside of the peak maxima. At higher ppm where the longer peak begins to dominate the full SIE again works best. The SIE also works for the opposite shift from In₂[Pt(CN)₄]₃ showing that it is a very sensitive metrics for different behaving materials, but not for <40 ppm exposures.

Optical fiber displacement sensors (OFDS) offer several advantages over conventional sensors due to their compact size and immunity to electromagnetic interference. These are particularly useful for applications in confined spaces, including aeronautical turbines. The critical component of OFDS is the fiber bundle, whose response depends on the arrangement, radius, and number of fibers. We developed a straightforward yet effective method for designing OFDSs based on sensor specifications: working point, range, and sensitivity. This allows to determine the bundle geometry directly from the specified requirements. Among the explored designs, the tetrafurcated bundle stands out, composed by a transmitting fiber at the center, surrounded by three collections of receiving fibers. This paper demonstrates that tetrafurcated OFDS designs significantly enhance both the range and linearity. Additionally, they effectively reduce the dead zone of the sensors, enabling precise measurements even at very short distances. The design has been manufactured and experimentally validated. Simulation and measurements are in good agreement with an MSE of 0.26%. Our findings highlight the practicality and reliability of tetrafurcated OFDS designs, opening new possibilities for advanced displacement sensing applications.

The purpose of this work is to explore the use of optical resonators based on the Whispering Gallery Mode phenomenon (WGM), to determine the variation of the internal pressure of a pipeline due to leaks. Numerical experiments were performed to determine the sensitivity of disk-shaped optical resonators embedded in the wall of the pipe. A change in the internal pressure causes mechanical stress in the pipe wall and therefore a strain that is transferred to the optical resonator. This strain can be related to the shift of the optical modes (WGM shift) to determine the sensitivity of the sensor. The parameters investigated include the size of the resonator and the location within the thickness of the pipe wall. The results show a linear behavior of the WGM shift with the applied pressure, as well as a quadratic increase of the sensitivity with the resonator diameter.

This paper aims to evaluate the performance of several supervised machine learning methods as to determine the best algorithm for detecting explosives with multispectral imagery. Ocean Thin Films SpectroCam with 8 interchangeable band pass filters is used to collect images. The stack of 8-dimensional data cube can be obtained and subsequently analyzed with various machine learning algorithms. We specifically study four classifiers: Convolutional Neural Network, Support Vector Machine, Quadratic Discriminant Analysis, and Linear Discriminant Analysis. We examine and compare the accuracy of the four classifiers’ performance in the application of detecting trace C4 material. Our results show that the Support Vector Machine and Convolutional Neural Network classifiers achieve the best overall accuracy, although they have the longest training time.

This work presents the improvement of the control methodology for a robotic smart foot with optical sensors to proprioception and using a hybrid adaptive controller with fuzzy logic and PID. To do this, the adaptive controller performs analysis in 50ms interactions, indicating the necessary adjustments to the PID controller gains. Therefore, experiments were carried out in various scenarios and the adaptive controller was compared with the conventional PID controller. As a result, the adaptive controller showed an improvement in overall performance when applied in scenarios with different ground inclination angles.

The analysis of the quality and selection of green coffee beans is currently performed using sensory methods, following the SCAA cupping protocol, which yields qualitative results. Evaluators assess 11 different sensory attributes of the coffee, using a 300 g sample roasted lightly for 10-15 minutes over a direct flame. The roasted sample is then ground and divided equally into 5 pots, infused with water, and allowed to rest for 5 minutes. Following this resting period, sensory analysis is conducted, with scores assigned to each attribute on a scale of 0 – 10. This procedure is carried out independently and in triplicated. In the day-to-day operations of a coffee roasting plant, it is important to maintain control over each batch of raw coffee and ensure that the roasting process is followed accurately. Currently, this evaluation process requires a complex and comprehensive infrastructure. However, advancements in optical and computational capabilities have opened new possibilities. Consequently, this research aims to explore the application of fluorescence spectroscopy on raw coffee samples and utilize chemometric techniques to separate and classify the beverage profiles.

Monitoring pitting corrosion in real-time and non-destructively is a critical challenge in material science. This study introduces dynamic speckle analysis as an innovative approach to quantitatively track pitting corrosion in metallic structures. Pitting corrosion, a major cause of structural failure due to hole formation, is effectively visualized using this technique. Dynamic speckle patterns, generated by laser light scattering off the corroded surface, reveal both the activity and progression of corrosion. We employ a range of graphical and numerical statistical parameters for detailed analysis. Notable for its low cost, ease of implementation, and quasi-in-situ capabilities, our method offers a significant advancement in the study of corrosion. It holds great promise for broader applications in both natural and industrial settings, presenting a versatile tool for material degradation assessment.

The spectrometer free areal chromatic confocal metrology (ChromaCAM) is an optical 3D surface measurement technology, which allows a simultaneous measurement of a large array of measuring points within a single exposure. In this work, we investigate the accuracy of a first prototype sensor system utilizing this new singleshot 3D measurement technique. It is found that surface height measurement errors smaller 1μm within a total measurement range of about 1000 μm are achievable. Furthermore, several influential factors are investigated showing the advantages and limits of the presented system. Investigating different surface materials it is found that frame rates up to approximately 800 fps for highly reflecting surfaces and up to 30 fps for ceramics, aluminum, and plastics are achievable.

The spectrometer-free chromatic confocal measurement technique enables 3D surface measurements with just one exposure and without scanning. To reduce the need for a spectrometer for the spectral analysis of the reflected light composition and thus the extraction of the local surface height, an optical spectral analysis unit is used. This unit determines the first momentum of the spectral composition reflected from the surface under probe for a large number of lateral measurement points simultaneously. This work investigates the impact of the spectral composition and light power of the light source on the sensitivity and accuracy of this method. A thorough optimization of the light source will be conducted, demonstrating the impact of various spectral compositions and light source power on the system performance, taking into account the system-related etendue. In addition, the optimization of the spectral transmission filter used in the optical spectral analysis unit and its influence on the accuracy and sensitivity of the system over the entire measurement range is shown.

Geometrical calibration is a crucially important step for numerous applications of digital cameras. We decribe an automated cloud-based solution that allows anyone with an Internet connection to calibrate a camera in minutes. The necessary hardware includes only a tripod camera mount, a ruler, and a PC with a flat screen. The user is not expected to command any advanced skills; the procedure involves basic camera operation and simple file manipulations. Upon completion, the user obtains camera parameters as well as multiple detailed reports, characterizing the quality of the input data, the model-to-data consistency, and the expected uncertainties of the calibrated model. In addition to a brief overview of the system architecture and capabilities, this paper focuses on the key part of the method: the processing of input data and the circumvention of automatic “image improvement” mechanisms that are ubiquitous in modern cameras and often cannot be disabled.

Light Sensing and Ranging (LiDAR) is a widely used technique for reconstructing three-dimensional (3D) scenes in a variety of applications, including augmented reality and virtual reality, automotive, industrial machine vision, earth mapping, planetary science, etc. Recent progresses in 3D stacking technologies provided an important step forward in SPAD or SiPM array development, allowing to reach smaller pitch, higher pixel count and more complex processing electronics. However, these also have certain disadvantages that should be considered in specific applications that as limited dynamic range, afterpulsing, crosstalk, and noise. For example, SiPM exhibit dark counts, which are spurious signals generated in the absence of incident photons. Dark counts contribute to the noise floor of SiPMs and can limit their sensitivity, especially in low-light conditions. Efforts are made to reduce dark counts, but they still exist to some extent. Therefore, we have quantitatively analyzed the limits of SiPM compared to APD in a noisy environment in this paper. For example, when the target size is constant, and the beam size is larger than the object, the SNR (Signal-to-Noise Ratio) of the pulsed signal due to ambient light can be analyzed mathematically.

Understanding the mineralogy of the Moon is key to viable mining and mineral processing necessary for the utilization of resources on the lunar surface. As on Earth, the minerals present in a resource can have drastically different physical and chemical properties, and require varying processing protocols to extract useful materials. The mineralogical and chemical complexity of lunar material requires more detailed analysis than simple observation of the elemental composition for detailed scientific understanding, or successful resource extraction. However, traditional non-contact sensing suffers from either low spatial resolution, or the inability to collect data fast enough to enable real-time decision making. Real-time data facilitates selective mining of target minerals of interest, and the optimization of mineral feeds consistent, high yields of extracted resources. Fluorescence analysis can obtain detailed mineralogical information at a high spatial resolution, while still being able to analyze bulk areas at speeds rapid enough such that precise mining or mineral processing control operations can occur. Useful fluorescence from minerals does occur, especially in the near-infrared (NIR), with these ‘novel fluorescence’ peaks standing out in an otherwise low-background emission waveband range, and are additionally enhanced at cold temperatures. This is demonstrated through the detection of NIR fluorescence discovered from specific minerals important for metal, oxygen, and water extraction on the lunar surface. The practical implementation of sensing devices utilizing this novel fluorescence is discussed, showing that simple and reliable systems can be designed which locate high-value lunar minerals in real-time with minimal data processing or deconvolution required.

In the automotive industry, new material combinations and optimized designs enable material savings and weight reductions. However, during welding, the different properties of the materials lead to structural changes and in-fluence the strength of the joint. Testing of the resulting intermetallic phase is of crucial importance for safety-relevant components, which currently often requires complex and destructive methods. The aim of the project is to develop a fiber-based, endoscopic LIBS (Laser Induced Breakdown Spectroscopy) system that enables spatially resolved determination of the material composition of welded joints in cavities or complex deep-drawn components of wrought aluminum alloys. The proposed method offers advantages in terms of measurement speed and reduced sample destruction.

Ghost imaging (GI) as a tool for the indirect estimation of two-dimensional information by using a single detection unit is of high interest in different fields of industrial and academic applications. One of the crucial benefits of such a technique is the flexibility of the single detection unit, which may, for example, consist of an avalanche photodiode that can provide several orders of sensitivity compared to PIN diodes. In this work, a combined technique is proposed using a high frequency (1MHz) modulated color selective light source together with a phase sensitive amplifier for the detection of incoming light from low scattering technical surfaces. The aim of this work is the proposition of the optical metrology approach in combination with an application-optimized set of the necessary illumination patterns to reduce acquisition time. Instrumentalization of the modulation phase information of the scattered light enables estimation and visualization of the fluorescence of the surfaces e.g., organic contaminations. The target application for this technique is the estimation of typical surface properties (roughness, homogeneity) for monitoring of additive manufacturing procedures in industrial, highly light-contaminated environments. Due to the high-speed switching time between different light sources, a fast operational acquisition of the spectral image data is achieved enabling the resulting measurement approach for inline applications.

This paper outlines the development of a new method of aircraft detection for the purpose of ensuring air traffic safety during outdoor laser operation. Outdoor laser use poses hazards to air traffic, and thus the Federal Aviation Administration mandates safe operating distances between the laser beam and aircraft. The positions of aircraft are determined by decoding their Automatic Dependent Surveillance-Broadcast transponder messages, and hence the distance between aircraft and the location of the beam can be calculated. This distance information is used to cease laser beam transmission into the sky within the FAA-compliant distance. This paper describes the software developed to read, organize, and analyze the data transmitted from aircraft, the processes to find potentially hazardous encounters in this data, and the methods to cease laser usage once hazards have been determined. This system is designed to be implemented for use in the Culebra Aerosol Research Lidar project, but has potential applications for laser satellite communication, laser guide stars, or laser shows.

Photonics’ potential has changed various industries. Device and system security is important as photonics technology advances. Physical risks and photonics asset protection are examined in this work. Post-silicon device and system integrity is tested utilizing side channel signal analysis, fault injection assessment, reverse engineering, electrical and optical probing, and photonic emission analysis. Chips, imaging, probing, electrical characterization, and spectroscopy are needed for these methods. Even with breakthroughs in failure analysis and side channel measuring devices, attackers may use these systems to attack and expose critical data, cryptographic keys, firmware, configuration passwords, and intellectual property. Physical attacks weaken encryption and security, giving unauthorized access to embedded system assets. All physical attacks and remedies are covered in this special issue on photonics assurance security. Photonics assurance research on limiting physical hazards and safeguarding photonics-based devices and systems is included in this special issue. Our actions will keep photonics technology safe and foster innovation across industries.

Optical reflectors are essential components used in spectroscopy applications that require high-intensity and uniform sample illumination. Typically, reflector parameters such as curvature and dimensions are optimized to ensure efficient light direction from filament lamps to the sample under test. Elliptical reflectors are often used to collect all the light emitted from one focus and direct it to the other. However, the curvature of miniature reflectors can be challenging to evaluate using standard measurement tools and methods due to its high aspect ratio, which can present mechanical and optical limitations when trying to access and scan it. In this work, we report a characterization procedure to evaluate the different optical and dimensional parameters of a fabricated miniature elliptical reflector with a high aspect ratio of width to depth. We compare two fabrication methods, Plastic Molding, and Diamond Turning, to assess their effectiveness. The reflector's curvature is characterized using the negative shape filling method, where melted polymer is used to fill the reflector and allowed to cool until solidified, resulting in a negative convex shape of the reflector. The reflector's curvature is then calculated by fitting the shape to the appropriate elliptical function using image processing. This method shows good accuracy in evaluating the reflector's curvature. Furthermore, the reflector's optical performance and illumination spot are characterized by imaging the spot onto a target screen and detector, validating the good performance achieved with low-cost plastic molded reflectors compared to DT reflectors. The image quality and optical power identify surface roughness and coating quality, where the molded reflectors show better results compared to the DT reflector.

Diffused reflectance infrared spectroscopy is well known as a compact, low-cost, and efficient handheld spectrometers. One of the spectrometer’s most important optical parameters is the effective collected spot profile from diffuse reflection samples not the simple illumination spot which determines the analyzed sample portion defining the spatial resolution. In this work, we present a novel method for characterizing the spot size based on the Knife-Edge technique. A sharp high scattering material such as PTFE is displaced into the spectrometer optical interface on a 1-dimensional moving stage while capturing the power at each step. Then by differentiating this cumulative power, the intensity spot profile is obtained and fitted to a Gaussian profile where the spot size is defined as the diameter that contains 90% of the reflected power. MEMS FT-IR spectrometers with different spot sizes measured as a demonstration of the technique. Moreover, this method quantifies different other parameters such as Goodness of Fit, spot lateral shift in addition to spot shape wavelength dependence that may occurs due to any non-ideality in the spectrometer system.

Fibre thermosetting composites play a major role in the engineering of advanced structures due to their combination of light weight and high strength and stiffness as well as the design flexibility. The high manufacturing cost and the inherently low production rates are the main limiting factors in increasing adoption of composites which can be overcome through the development of manufacturing strategies, materials and methodologies of process optimization and control. An accurate estimation of the stage of cure of thermosetting composites production is critical to deduce the overall process duration and ultimately the manufacturing costs. Challenges arise due to temperature overshoots and lack of direct measurement and control of the cure stage, particularly in thick components where the effects of the exothermic nature of the curing reaction and composite low thermal conductivity are more pronounced. To address these challenges and enabling the real-time process optimization, this study proposes a novel approach based on a machine learning (ML) model using simulation Finite Element Method (FEM) data as well as PIC-based photonic sensors realized on Silicon-on-Insulator (SOI) platform. Two robust Voting regressors, XGBoost and Light Gradient Boosting Machine, are used in the model to accurately (98% accuracy) predict two critical parameters: Cure time and Temperature Overshoot. Using photonic sensors to monitor the process in real time, we present experimental validation of Overshoot on manufacture RTM-6 aerospace composite parts.

This paper discusses a methodology based on the free space depth measurement scheme facilitating the allocation of the real optical axis relative to the newly established datum resulting from the presence of a mechanical attachment. The methodology only requires depth data in one direction and the DUT does not need to be perfectly aligned with the sensor. This, in turn, enables an in-situ optical alignment capability in the mass-production environment, where position accuracy and repeatability are critical.