This PDF file contains the front matter associated with SPIE Proceedings Volume 13449, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

Handheld Raman sensors hold the key to generating real-time information about product quality and safety, which can result in significant savings in time and money. Sensor developments coupled with powerful chemometric modeling allow extracting unique information from complex multi-spectral matrices data improving the sensitivity and specificity of analysis facilitating quality control and detection of food contaminants and adulterants. Implementation by the industry and regulatory agencies of rapid testing procedures based on miniaturized sensor technologies would help to streamline quality assurance and food safety. We will present information on handheld systems that allow for “real-time” analysis helping the industry to effectively monitor product quality and implement mitigating approaches.

Vibrational spectroscopic imaging offers valuable insights for various applications. However, acquiring and processing data over a full spectral range can be time-consuming and there is value in optimizing the acquisition and processing times to enhance the efficiency of vibrational spectroscopic imaging. There are several optical configurations that can be employed to accelerate the image acquisition and generation process. One such technique utilizes Raman spectroscopy, which has the potential to increase speed by combining data acquisition over a narrow spectral range with laser raster scanning. For certain samples, the Raman spectral responses can be focused on specific spectral ranges, allowing for faster data acquisition compared to techniques that cover a wider spectral range. This speed enhancement enables faster analysis and imaging of samples, making it a valuable technique for applications where time is a critical factor. The initial results will showcase the potential and capabilities of this image generation process. The presentation of initial results will provide valuable insight into this new imaging modality.

Detection of infrared (IR) spectrum features of target molecules can be achieved by comparison experimentally measured spectra to template spectra within a database. This study continues presentation of the concept of using density functional theory (DFT) for calculation of template spectra. DFT-calculated spectra are well posed for comparison to measured spectra, to the extent of their scalability to larger space–time scales. Specifically, the focus of this study is the scalability of DFT-calculated IR spectra with respect to meso- and macroscales, characteristic of dielectric response as measured using different IR spectroscopies. A case-study analysis concerning IR-spectra scalability for a set of energetic materials is described. This analysis provides another example of calculating template spectra for potential detection of target molecules, which are of major interest using IR spectroscopies.

Artificial Intelligence (AI) and associated topics (e.g., machine learning, neural networks, deep learning, reinforcement learning) are receiving significant attention in the scientific literature and the popular press. For example, in early March of 2025, Richard Sutton, (a computer science professor of the University of Alberta, Edmonton, Alberta, Canada, and one of the founders of modern computational reinforcement learning), has been a co-recipient of the 2024 Association for Computing Machinery A.M. Turing Award (often referred to as the “Nobel Prize in computing.”). A co-recipient of this award was Andrew G. Barto (a Professor Emeritus, Department of Information and Computer Sciences, University of Massachusetts, Amherst, USA). In addition, the 2024 Nobel Prize in Physics was awarded to John J. Hopfield (Princeton University, NJ, USA) and to Geoffrey Hinton (University of Toronto, Canada) “for foundational discoveries and inventions that enable machine learning with artificial neural networks”. Surprisingly, the same year, Nobel Prize in Chemistry was award in a related field (for instance, development of computational approaches in Bio-Chemistry for protein folding and “structure prediction”). This Nobel prize was awarded to David Baker (of the University of Washington, Seattle, WA, USA and of the Howard Hughes Medical Institute, USA), and to Demis Hassabis (of Google DeepMind, London, UK) and to John Jumper (of Google DeepMind, London, UK) for “protein structure prediction”. In addition, the “environment program” of the United Nations (UN), has published an informative document entitled “how Artificial Intelligence is helping tackle environmental challenges”.

Variations in the optical collection efficiencies, which are a function of wavelength and position, confuse the actionable information from a spectroscopic sensor with time varying spatial non-uniformities across the optic. Averaging measurements over the dynamic time of the features of interest mitigates these dynamic spatial nonuniformities but slows the actionable response time of the detector. As such, we designed a compact (3.5in by ⌀ 1.5in) ruggedized, achromatic, illumination optics system. The coupling optics create a radially flat collection efficiency for all wavelengths of interest, until maximum radial aperture of the application. The optics transmit the uniform collection to a commercially available miniature spectrometer via a fiber optic cable. A manufactured system probed with a point-like, calibration light source holds a 2.5% spectral ratio uniformity through a ∼1/2 in aperture.

We present the optical module design of Enfys, a pencil-beam, non-imaging, infrared (0.9-3.2 μm) spectrometer for the ESA ExoMars mission. The instrument comprises a novel optical architecture based on travelling linear variable filters (LVFs) and infrared photodiodes; a solution devised to be rapidly deployable with low technical risk while maintaining sufficient performance to satisfy the instrument’s scientific goals. The design uses aspheric surfaces decentred from the optical axis to optimise spectral resolution and maximise energy throughput within a compact space envelope. We outline the principal trade-offs incurred in such an optical construction and show the results of simulations and preliminary measurements to determine optical performance. Simulated full-width-half-maximum spectral width is shown to be less than 1% of the peak wavelength over the bulk of the operating waveband.

This research presents an experimental and simulation-based study on the performance of a gold-coated retroreflector designed to operate in the visible to infrared (500 nm - 1600 nm) spectral range, with potential applications in free-space optical (FSO) communication and UAV-based systems. The retroreflector, with a 2 cm² integrating sphere, was tested experimentally to measure its specular reflection properties under varying conditions of bed temperature and initial beam line width. These conditions were selected to simulate typical operational and environmental stressors that a UAV or optical communication system might encounter. Experimental measurements of the specular reflection coefficient were obtained across a range of bed temperatures, simulating the thermal gradients that could be experienced in high-altitude or varying climate conditions. Additionally, different line widths were applied to assess the retroreflector’s performance under diverse optical alignment scenarios, relevant to practical deployments where beam divergence and alignment errors could degrade signal quality. The experimental data, specifically the reflective values, were subsequently employed in Optsystem simulations to evaluate the power returned from the retroreflector under different atmospheric conditions, including clear and cloudy skies, with varying rain rates. These simulations were critical in assessing the degradation of signal power due to absorption, scattering, and atmospheric turbulence, which are common challenges in FSO systems. The simulation results demonstrate how environmental factors affect the returned power, which is critical for applications in optical communication systems, UAV navigation, and tracking systems in adverse weather conditions. This study paves the way for further research into optimizing retroreflective materials and system configurations for real-world applications, including satellite communication and UAV-based systems operating in diverse meteorological environments.

A variety of microplasmas have been fabricated and have characterized with a variety of analytes. In an attempt to improve signal intensity, excitation temperatures were measured as be described in detail in this paper.

Optical sensing instrumentation has gone through significant advancements and innovations over the last decade with the development of fast and reliable sensors and imagers. Propelled aircraft and missiles have detectable signatures though the whole range of the spectrum spanning from the ultraviolet (UV) up to the near and mid-infrared bands (NIR and MIR, respectively). Advanced electro-optical/infrared (EO/IR) sensor suites are critical assets that give tactical and situational advantages for both military and civilian applications. The knowledge of the exact transmission spectrum of an instrument is critical for the analysis of collected data and maximal extraction of information, and it is usually achieved using calibrated spectrometers that can cover the desired wavelength band of instrument operation.

RadiaBeam Technologies is developing a Wideband Advanced Spectrometer Platform (WASP) that will constitute a compact measuring and calibration instrument. The instrument is based on the use of bandpass linear variable filters (LVF) to allow fast and reliable spectral analysis that covers the entire 200-14,500 nanometers (UV-MIR) wavelength range. A laboratory prototype of the instrument covering selected sub-bands has been designed, integrated and tested at RadiaBeam. This paper will report on the optomechanical design, integration, and spectral performance of the laboratory WASP prototype, with highlights for a future fully functional instrument.

Electron paramagnetic resonance (EPR) spectroscopy is a valuable tool for studying objects with cultural heritage significance, especially paintings as many renaissance era pigments have an EPR signal. Unfortunately, EPR is invasive for all but mm size objects. Although EPR is not destructive of the sample, some heritage conservators consider it destructive of the cultural heritage object as sampling requires removal of a small portion of the object. The EPR mobile universal surface explorer (MOUSE) is a more portable EPR spectrometer useful for noninvasively and nondestructively studying a 3mm diameter region of any size object. With the MOUSE we have identified single, mixed, and layered paramagnetic pigments in paint on canvas, and imaged the distribution of paramagnetic and ferromagnetic pigments on canvas, both on the surface and from underpaintings. This paper summarizes these capabilities, recent hardware developments, such as the scannable unilateral permanent (SUPER) magnet, for the EPR MOUSE.

Terahertz (THz) technologies utilise wavelengths ranging from 30 to 3000 μm; a non-ionising segment of the electromagnetic spectrum. Efforts are ongoing to leverage THz technologies for commercial sensing and defence applications. However, the signal strength of free-space THz waves is reduced from atmospheric water vapour—a significant challenge to overcome. A typical mitigation strategy is to displace the water vapour with nitrogen in a controlled setting. This mitigation strategy is not feasible for many imaging and remote sensing applications. To address this, signal processing techniques for the enhancement of free-space THz signals via a nonlinear filtering method, such as the extended Kalman filter (EKF), have been initially explored by Spotts et al. We present an extension of these initial works by modelling the atmospheric water vapour for a 2 state EKF filtering algorithm towards the enhancement of THz signals.

Pulsed THz waves are heavily influenced by the presence of water vapour manifesting as perturbations in the time-domain signal, corresponding to attenuated spectral content in the frequency-domain. We validate a vapour model through application of a 2 state EKF non-linear estimator on a dry nitrogen THz signal. The treated time-domain THz signal shows high levels of agreement with a control measurement, being a water vapour THz signal. The EKF vapour model is further validated in the frequency-domain, with the spectral content of the water vapour vibrational modes matching that of the control water vapour THz signal and the HITRAN database. The treated THz signal corresponds to a 95% reduction in error between vapour THz signal (control) and the dry THz signal.

It is envisioned that these initial findings can be leveraged in future works to enhance the application of THz technologies towards commercial sensing and defence, by reducing the effects of water vapour interference on THz signals via the EKF.

A flexible and reflective stereo-metamaterial (SMM) was fabricated in a strain-sensitive soft backing layer of polydimethylsiloxane and polyimide (PI-PDMS-PI) substrate. The SMM consists of coupled copper rings designed to interact with terahertz (THz) radiation. Up to 5.5% compressive strain was applied to change the resonant frequencies of Cu-coupled metamaterial rings detected through polarization status. Upon application of compressive strain, a blueshift was observed in the frequency-switching response related to the ellipticity of the reflected THz waves. This shift indicates that the SMM structure's resonant properties are sensitive to mechanical deformation. To characterize the polarization state of the reflected THz waves, the four individual Stokes parameters (S₀, S₁, S₂, S₃) and their normalized forms were investigated and analyzed using polarimetric THz time-domain spectroscopy (P-THz-TDS). These characteristics, along with the device's ability to recover when relaxed, suggest potential applications in areas such as structural health monitoring, wearable electronics, and adaptive THz optics.

In 1935 there appeared two articles Physical Review having the same title. In the first of these, authors Albert Einstein, Boris Podolsky, and Nathan Rosen (EPR) formulated their famous EPR paradox to demonstrate their supposition that Quantum Mechanics cannot provide a complete description of physical reality. This was the birthplace of so-called Local Hidden Variable Theories intended to ‘rescue’ quantum mechanics from its apparent failure as Locally Realistic theory. In the second of these articles, author Neils Bohr responded by pointing out that the fundamentally invasive nature of the measurement process essentially precludes simultaneous well-defined values of incompatible observables as elements of physical reality. Interestingly, there was a third voice, that of Arthur Ruark, who pointed out in a letter to the editor that, at least in 1935, there was really no way to tell who, if anyone, was correct. Further, there appeared also in 1935 and article in Naturwissenschaften by Erwin Schrodinger in which he formulated his famous “cat paradox” in order to demonstrate the non-classical (and non-local!) implications of quantum entanglement. In fact, the conceptual import of this pair-o-paradoxes is informally often referred to as the “spooky action-at-a-distance” feature of Quantum Mechanics. Fast forward to 1964 when John S. Bell provides a formulation of Bell’s Inequality, which christens a robust method for deciding the validity of Local Hidden Variable Theories as opposed to that of Quantum Mechanics. Bell’s Theorem and subsequent seminal experiments have placed Quantum Mechanics on solid ground as a tool for describing physical reality. This has resulted amongst other things in the evolution of quantum entanglement as a resource for quantum information processing, sensing, and communication. In this talk, I will review several interesting results we have obtained based upon violations of the Clauser-Horne-Shimony-Holt (CHSH)* form of Bell’s inequality. This form is the appropriate form for the continuous variable quantum states we have examined, namely entangled coherent states of the semi-simple Lie Groups SU(2) and SU(1,1). The entanglements and the measurements we consider are based upon the dichotomic group parity operators for each case. I will do my level best to discuss implications of our work, specifically as a form of continuous variable quantum entanglement witness.

Miniaturized sensors or portable micro-instruments that can be used for measurements on-site (i.e., in the field) are essential, for instance, for IoT (Internet of Things) applications, for Industry 4.0/Industry 5.0 applications, and (for chemical analysis applications) for “bringing part of the lab to the sample” (e.g., for making measurements in the field).

Ideally, devices or systems (e.g., sensors or instruments) must be operated in the field from energy harvested from the ambient (e.g., solar or wind instead of using a battery). One example of energy harvesting is by employing Tribo Electric Nano Generators (TENGs). In my lab and for the last several years, we have been working on TENGS for energy harvesting applications. In this paper, continued work and further developments TENGS will be described here.

The natural gas sector is constantly demanding for non-invasive, self-standing and consumables-free approaches capable to measure the composition and hence the thermodynamics properties of the mixtures flowing in the network. A novel approach is represented by Raman spectroscopy as the only full-optical method able to measure simultaneously the mixture composition, including gases difficult or impossible to be measured with conventional spectroscopy, such as hydrogen and nitrogen.
In this work, the latest developments regarding a novel industrial-grade instrument are presented. The Raman emission is triggered by a broadband solid-state laser diode with emission centered at 455 nm, that is stabilized in temperature by a TEC controller. The laser beam is focused into a gas-cell which can operate with an internal pressure up to 17 absolute bar, compatible with pressures found in the transport network. The Raman scattering is collected at 90° angle by a high-luminosity (f/2.4) objective + spectrometer. The experimental spectra are finally analyzed via a custom-made fitting procedure giving the mixture composition, the Heating Value and the mixture density.
The performance has been characterized in terms of composition measurements and related calculation of the mixture thermodynamics properties over the full required environmental temperature range (from -20°C to 50°C) and at sample pressures up to 17 absolute bars. The results comply the metrological requirements for all mixtures tested: different natural gas mixtures with different content of heavier hydrocarbons and impurities, hydrogen-enriched natural gas mixtures and methane-hydrogen binary mixtures.

The process and quality controls associated with toxic industrial chemical (TIC) and chemical warfare agent (CWA) vapor generation and algorithm validation for field portable FTIR systems are presented. Techniques for pure vapor generation, as well as inclusion of environmental and interferent conditions, and quality verification for system validations are discussed.