Optical Instrument Science, Technology, and Applications IV

The discrimination between protein families within their native biological environment without the use of labeling strategies remains a major challenge in biological imaging. In this study, we introduce an original approach that takes the advantage of the non-resonant background (NRB) signal in Multiplex Coherent Anti-Stokes Raman Scattering (M-CARS) spectroscopy. Such a signal is typically considered to lack specific information. By exploiting the contrast between resonant and non-resonant components in hyperspectral M-CARS datasets, our method enables the label-free identification and spatial mapping of distinct protein families. As a proof of principle, we successfully discriminate actin and myosin filaments in muscle tissues. Myosin localization is determined through its intrinsic second harmonic generation (SHG) signal, while pixel-wise analysis of resonant-to-non-resonant ratios reveals the distribution of actin filaments, in concordance with independent measurements conducted using SHG. This work demonstrates that the often-overlooked silent spectral region contains valuable information for protein discrimination, and underscores the potential of nonlinear optical contrast to expand the analytical capabilities of M-CARS for complex biological systems.

We present a contactless, camera-based sensor system for monitoring vital signs (respiratory rate, heart rate, and SpO2) using a real-time multispectral snapshot camera with seven distinct bandpass filters in the visible and near-infrared. The camera features a single hot-embossed glass lens array enabling approximately 1.25 MP per channel at F/4 with a 40° field of view, combined with LED illumination and dedicated read-out/control electronics. Everything is assembled in a compact sensor head measuring 85 x 85 x 160 mm³. We outline preprocessing of multispectral data and remote photoplethysmography (rPPG)-based respiratory rate (RR) estimation. In initial evaluation with 12 individuals, RR is estimated with a mean absolute error of 1.28 bpm and 95% limits of agreement from -4.02 to +3.98 bpm. Critical influencing factors are discussed. We present the optical design, realization and application of this novel demonstration system.

Photonic metasurfaces have tremendous potential to miniaturise optical measurement systems. In this work we demonstrate this by realising a novel fibre-linked chromatic confocal sensing (CCS) probe approaching the size of a grain of rice (5.5 mm long, 3 mm diameter), with a weight of less than 0.1 g while maintaining an axial measurement range of over 100 µm. The optical performance and measurement capability of the metalens CCS probe is demonstrated in preparation for planned use within a single-point diamond turning machine for surface topography measurement. We also discuss the use of two-photon polymerisation printed components as a method to facilitate minaturized probe assemblies.

Retinal endolaser photocoagulation is a vitreoretinal procedure that uses a fiber-based endolaser probe to treat a range of retinal diseases. Intraoperative sensory feedback could greatly improve safety and treatment precision, but slit-lamp-based systems struggle to track a moving probe, and the small size of intraocular instruments limits sensor integration. We present a fiber-optic smart instrument capable of both surgical laser delivery and real-time tomographic monitoring of tissue changes. The surgical and OCT beams are co-axially transmitted through the outer multimode and inner single-mode cores of a dual-clad fiber. A 300 µm 3D nano-printed aspherical microlens at the fiber tip optimizes beam shaping for both wavelengths in the vitreous. We describe the probe’s design, fabrication, and ex vivo validation in porcine eyes.

Rover-borne laser spectroscopy has traditionally been supported by contextual 2D imaging. We present a low-cost, miniaturized projector designed for the space environment, which is capable of active phase shifting fringe-projection. It consists entirely of individual off-the-shelf optics housed in simple mechanics. Whilst scalable to different applications, it is integrated here inline in a combined NIR microscope / Raman spectroscope to allow construction of highly resolved 3D spatial and chemical maps of astrogeological objects. Requirements, architecture and trade-offs are discussed before calibration and 3D performance results are shown, before 3D measurements from a geological sample are presented.

In this paper we build on our machine vision camera simulation by modeling an automated metrology instrument. Metrology instruments are critical to high-volume manufacturing, however, validating these systems in hardware is a time-consuming, resource-intensive process. Simulating the validation process in lieu of hardware reduces program risks and costs while simultaneously speeding the path to production. By combining lens design, virtual twin and statistical software, we propose a novel method to simulate metrology instrument variability to enable a team to accelerate production workflows. Simulated gage repeatability and reproducibility (GR&R) is computed from model data using industry standard tools to predict the gage capability of the instrument system digital twin. This approach allows teams to prevent potential GR&R failures and catch design issues if a solution only marginally meets pass/fail criteria.

The Copernicus CO2 Monitoring (CO2M) satellite is a key component of the European initiative for CO2 Monitoring and Verification Support (CO2MVS), designed to monitor global anthropogenic CO2 and CH4 emissions. Thales Alenia Space in Switzerland (TAS-CH) developed the Telescope for the CO2 Imaging Spectrometer (CO2I), one of the three primary instruments onboard CO2M. The Telescope serves to depolarize light reflected from the Earth’s atmosphere and guide it into the near-infrared and shortwave-infrared spectrometer. The CO2M Telescope features an off-axis Three Mirror Anastigmat (TMA) optical design, supplemented by two folding mirrors at both the entrance and exit to meet interface requirements. A polarization scrambler, based on the Babinet principle and utilizing pairs of wedged birefringent prisms made of crystal quartz, is located at the telescope entrance. A custom optical coating for the scrambler was developed and qualified to ensure optimal performance. The main technical challenges in the telescope’s development included: i. integrating the complex optical system within a robust and thermally stable opto-mechanical structure; ii. achieving mass optimization, necessitating significant lightweighting of the larger glass mirrors; iii. designing and implementing the polarization scrambler; iv. developing strategies for optical alignment, assembly, integration, and testing (AIT), along with the associated ground support equipment. The challenges and results of the qualification test campaign are presented. PFM telescope delivery will follow the completion of the test campaign and FM2 (flight model nr.2) AIT activities will start in parallel. This paper presents the telescope’s optical and thermo-mechanical design, and provides an overview of the Assembly, Integration, and Testing (AIT) campaign.

We are developing a compact three-element Wide Field Corrector (WFC) with spherical and aspherical lenses for the 2.34 m Vainu Bappu Telescope (VBT) to enhance its field coverage for imaging and spectroscopic applications. The design consists of three optical elements, with at least one spherical lens movable to serve as an Atmospheric Dispersion Corrector (ADC), while the aspherical elements remain fixed to maintain optical stability. We are currently testing two design configurations, one with two spherical lenses and one aspherical lens, and another with two aspherical lenses and one spherical lens. The ADC is designed to correct atmospheric dispersion for zenith angles ranging from 0° to 60°. The system is optimized to operate over a wavelength range of 0.4 μm to 0.9 μm, targeting an effective field of view of about 0.5°. Considering the limited mechanical space available at the VBT prime focus, the design emphasizes compactness, ease of alignment, and manufacturability. The system achieves a mean geometrical D80 better than 0.3″ and 0.23″ for Design 1 and Design 2, respectively, at zenith, and maintains a mean geometrical D80 within 0.57″ and 0.45″ up to a zenith angle of 60° after atmospheric dispersion correction. Atmospheric dispersion at higher zenith angles (up to 60°) is corrected using a movable lens element, enabling the system to preserve high image quality across the field.

Optical frequency combs revolutionized precision measurements and metrology over 25 years ago. Initially they were used to measure optical frequencies at hundreds of Terahertz in fundamental physics experiments, and to calibrate laser frequencies for interferometric distance measurements. Many more applications have emerged over the years. Advances in the accuracy, wavelength coverage, and ease-of-use of frequency combs have made them an essential tool in research labs and industry. In this talk we will introduce the concept of the frequency comb, and highlight some examples of applications that rely on them. We will also provide insights into new developments of compact, integration-ready frequency combs. Optical clocks require frequency combs as clockworks to operate with 18 digits of precision. Quantum computers based on cold atoms or trapped ions use lasers down to the Hertz-linewidth-level to address specific atomic transitions and write and manipulate Qubits. Such lasers can be conveniently realized via stabilization to a frequency comb. New generations of GNSS will use optical clocks, so frequency combs are being manufactured to be space-ready and autonomous, in particular for installation on the Bartolomeo platform on the International Space Station as part of the COMPASSO project.

The 20th and early 21st centuries have seen significant growth in the physical size and complexity of astronomical land-based telescopes. These scale increases, combined with tighter image-quality requirements arising from a combination of scientific demands and improvements in technology, have led to the development of active optics for telescope control, where wavefront sensors combine with actuators to drive the shape and position of optics in closed loop, correcting for deflections caused by gravity orientation and temperature changes. Active optics for large telescopes was conceived and developed in the late 1970s, 1980s, and 1990s, and, arguably, only brought to full maturity in the early 2000s. At this point in time, we stand poised on the brink of the Extremely Large Telescope (ELT) era, where apertures in the 10 m range from the 1990s generation of optical–infrared telescopes have leaped by factors of two to four in the upcoming generation of telescopes. At this scale, optical flexures and deflections are amplified compared to the current generation of telescopes, and the combination of open-loop modelling for initial optics positions and shapes, and wavefront sensing for closed-loop control and convergence, is seriously challenged. Since the late 2000s, a new approach, based on the direct metrology of optical components and instrument interfaces, has been developed. Direct metrology offers an interesting intermediate alignment stage between open-loop modelling of positions and closed-loop wavefront sensing. This paper discusses the development and application of these approaches to a range of large telescopes, including optical and radio telescopes.

This presentation will provide a comprehensive overview of European Space Agency (ESA) ongoing efforts to prepare for the next generation of optical Earth Observation missions. First, we will present the science-driven Earth Explorers and Scout missions addressing key scientific issues, followed by an update on preparations for future Meteorology and Copernicus missions. Second, we will present the pre-development activities of innovative instrumental concepts and associated technologies engaged to prepare the future of Earth Observation optical missions. Finally, we will highlight the activities focused on the preparation of compact optical payloads for small satellites.

The continuous shrinkage of semiconductor device size, as described by Moore’s Law, is a key driver of technological advancement. It allows placing more devices on a small chip and is essential for emerging technologies, e.g. AI, where the computational density and energy efficiency are paramount. Increasing the device density in chips requires innovations not only from the lithography but also in all other steps of the chip manufacturing loop, e.g. overlay control steps need to be performed at sub-nanometer precision levels. Optical overlay metrology faces several technical challenges, e.g. overlay targets becomes smaller as the device density increases. Measuring on a smaller target requires high-NA and high-quality imaging optics in overlay sensors, which lead to higher complexity and cost. Even with perfect lenses, cross-talks between the diffractions orders can lead to overlay error. The Digital Holographic Microscopy (DHM) concept offers potential solutions to these challenges. In the DHM, we image an overlay target on a camera using low-cost high-NA optics with only a few lens elements. It allows computationally correct for aberrations and cross-talks between the diffractions orders, and therefore offers near-perfect imaging for overlay metrology in a cost-effective way. In this talk we will share the insights on the state-of-the-art overlay metrology and the challenges. We will explain the DHM concept and demonstrate some of the solutions with simulation and experimental data.

This study presents a novel data acquisition and fusion framework for the optical multiscale reconstruction of hybrid porous materials. The framework comprises three key stages: (i) large-area topography reconstruction from focus variation to generate a coarse surface overview. (ii) selecting the measurement technique (such as confocal laser-scanning), scale and acquisition parameters best suited to the local geometry and structural properties of the respective porous features. (iii) hybrid 3D data fusion combining datasets from complementary optical configurations within a unified coordinate system. Through adaptive registration and merging, the approach enhances spatial consistency and topographic resolution, enabling accurate surface topography reconstruction of complex porous materials across multiple scales.

This work presents the adaptation and characterization of laser-induced plasma light sources as transfer standard light sources for radiometry and photometry after phaseout of incandescent lamps. These commercially available sources generate a point-like xenon plasma using a continuous-wave laser, producing broadband emission from the ultraviolet (UV) to the near-infrared (NIR). While it has been shown that these sources can be efficiently coupled to monochromator setups for applications that require spectral tuning, this study focuses on their utilization as broadband sources for spectral irradiance calibration using off-the-shelf optics for collimating and homogenizing the plasma spot emissions. Collimated, uniform irradiance distributions were produced using lenses for collimation and either diffusers or microlens arrays for homogenization. With the help of the microlens array, a uniform irradiance field was achieved at the measurement plane, with deviations of the measurement results under 0.1% for spectroradiometer entrance optics with a diameter between 10 mm and 30 mm. However, adding homogenization optics reduces spectral irradiance, particularly in the visible (VIS) and near NIR, compared to incandescent lamp standards. Temporal stability of about 0.5% was shown over repeated operation periods of several hours to days across the VIS to NIR spectral ranges. A different setup with a diffuser and a custom-built temperature-stabilized monitor detector produces similar temporal stability after correction. Strong xenon peaks and ozone absorption features remaining in the output must also be accounted for during irradiance calibrations. The trade-offs between spectral irradiance levels and spatial uniformity of the beam produced with different beam-shaping approaches are evaluated.

The global phaseout of incandescent lamps has created a need to establish alternative methods for ensuring metrological traceability of spectroradiometric measurements. Traditionally, incandescent lamps have been used as transfer standards across scientific and industrial domains, but their decreasing availability calls for new alternatives. To address this, a detector-based approach utilizing compact, portable array spectroradiometers supported by digital metrological twin as transfer standards has been developed. To support this approach, a dedicated Array Spectroradiometer Characterization (ASC) facility has been established at Physikalisch-Technische Bundesanstalt (PTB), Germany. It is designed to implement practical and affordable procedures for the comprehensive characterization of array spectroradiometers with respect to most important instrumental properties such as linearity, pixel-to-wavelength assignment, effective reference plane position and spectral stray light. The results obtained from characterizations demonstrate the suitability of array spectroradiometers as viable detector-based transfer standards for achieving traceability in spectral irradiance measurements.

LED-based illumination has become increasingly attractive for spectroscopy, imaging, and sensing applications thanks to their spectral diversity and compactness. However, efficiently combining the emission from multiple LEDs into a single, well-defined output remains a major optical design challenge. The overlap of multiple LED sources often leads to significant étendue mismatch, non-uniform illumination, and reduced optical efficiency. We present an overview of recent advances in the optical design of multi-LED systems, from state-of-the-art methodologies to a novel compact illumination architecture employing a single freeform mirror to collect and combine the LED emission beams. Particular attention is given to the role of the freeform mirror to spatially and angularly merge different LED channels, alongside an evaluation of the system’s optical efficiency, compactness, spectral homogeneity, and robustness. This design performance is supported by experimental validation within a proof-of-concept demonstration, paving the way towards its implementation in spectroscopic sensing applications.

The design of optics has seen very significant advances over the last seven decades or so, a lot of which has been due to the tremendous increase in the power of computing & software. In 1675, Isaac Newton said that “If I have seen further, it is by standing on the shoulders of giants”. The same is true of the optical designers of my generation in that we have benefitted so much from the work of the “giants” of previous generations. The presentation will therefore include brief synopses of the contributions of a few of these giants. Some selected examples will be given of the advances over the computer age in the means of designing optics and also the developments in specific optical devices. The presentation will be dedicated to the memory of John Greivenkamp, a great educator in optics, who was to have been its joint author.

Increasing screen exposure and reduced outdoor activity have contributed to a rise in binocular vision dysfunctions, highlighting the need for modern, technology-based training solutions. This study presents a head-mounted lens-filter prototype that automates binocular vision therapy using red-blue filters and interchangeable ±2.00 D lenses. Three gamified modules were developed to train vergence, fusion, and accommodation. In a trial with 23 participants, accommodative facility improved from 10 to 16 cpm, and positive fusional reserves increased significantly. The findings demonstrate that automated, game-based optical systems can effectively enhance binocular vision, offering a standardized and engaging alternative to manual therapy.

This paper presents a wideband microscope designed for the detection and analysis of extraterrestrial microorganisms within the solar system. An example of a conceptual design for a wideband microscope capable of observing the same field of view in the UV, VIS, and IR is shown; subsequently, the breadboard model (BBM) of the developed UV-VIS-IR microscope (UMI) is presented. To demonstrate deep UV microscopy (275 nm excitation) using the BBM of UMI, we observed a biological sample of sliced squid alongside four types of fluorescent mineral samples and compared the time-dependent changes in the images. As a result, the images of the sliced squid changed color over time, whereas those of all the mineral samples remained stable. We also presented the development of near-infrared (NIR) microscopic imaging spectroscopy and its required hardware for distinguishing organic matter from minerals. In the discussion, we first focused on the combination of microscopy with other methods: its combination with a mass spectrometer is complementary and highly effective. When designing life-detection missions for solar system exploration, ensuring scientific value—even in the event of a null result in the search for life—is crucial for the realization of the project. In life-exploration missions, it is meaningful to distinguish between 'Earth-kin life' (extraterrestrial life sharing a common ancestry with Earth life) and 'Earth-independent life' (extraterrestrial life that emerged independently of Earth life). We considered that if proliferation or autonomous movement is observed in the search for extraterrestrial life, it would serve as compelling evidence of life, depending on its appearance. The wideband microscope presented in this paper can be operated both with and without fluorescent dyes. We described that the use of fluorescent dyes in microscopy for extraterrestrial exploration of microorganisms offers advantages but also poses multiple concerns. The dye-free method presented in this study for identifying biological and mineral samples has the potential to serve as a solution to these concerns.

The “Deutsches Röntgen-Museum” in Remscheid (Germany) preserves a collection of X-ray images taken by W. C. Röntgen during his research. Among them are three images of Röntgen's own hands and those of his wife, Anna Bertha. Three more images show Röntgen's hunting rifle. These two series of historical pictures from the years 1895 and 1896 provide an outstanding illustration of the scientific revolution that Röntgen's discovery triggered especially in medicine and in materials science. In April 2025, those very first recorded X-ray photographs were added on the UNESCO Memory of the World Register. The corresponding public ceremony took place on September 10, 2025 in Röntgen´s birth town Remscheid. UNESCO is thus honoring not only Röntgen's groundbreaking discovery of X-rays, but also the cultural, scientific, and technological implications of his early radiographs.

We present a method for quantitative estimation of oil contaminant concentrations on metallic surfaces using reflection-based Fourier transform infrared (FTIR) spectroscopy combined with machine learning. Infrared spectra are acquired from aluminum alloy substrates carrying thin layers of two representative industrial oils at varying mixture ratios. A supervised partial least squares (PLS) regression model, trained on reference samples and optimized via cross-validation, maps measured spectra directly to predicted oil mixture concentrations. Despite variations in surface roughness and oil layer thickness, the model achieves a root mean square error below 3 % across a dataset of 4620 spectra. This approach enables quantitative, non-destructive identification of contaminant composition even for highly similar oil spectra, offering a pathway toward automated inline quality control of metal surfaces prior to coating or joining processes.

This paper is a summary of the SPICA Coronagraph Instrument (SCI) based on a review of previously published literature. The SCI is proposed for SPICA for the purpose of studying small-scale structures surrounding bright stars and galactic nuclei, which specifically include exoplanets (not only detection but also characterization of the atmosphere), protoplanetary and debris disks, dusty tori in active galactic nuclei, and interstellar matter around bright small-scale structures. High contrast images are produced in the SCI by using binary pupil-mask coronagraphs together with an image subtraction technique. The SCI is designed to have both the function of imaging (1’ x 1’field of view) and spectroscopic capability (R=200). The SCI possesses the capability of low-background spectroscopic coronagraphy over the continuous wavelength range from 4 to 28 micron. These specifications make the SCI a unique instrument for observations over a high dynamic range in the 2020s. After years of review in Japan and international review, the design of the instrument has been modified and simplified to reflect the scientific requirements. The SCI presently has neither a short channel nor a deformable mirror, both of which were present in the previous design.

This work presents an Optical Internet of Things (O-IoT) framework for smart urban mobility, integrating Visible Light Communication (VLC) and Deep Reinforcement Learning (DRL) to optimize traffic signal control in real time. Each intersection operates as an autonomous DRL agent, forming a decentralized optical IoT network where VLC enables low-latency, high-bandwidth communication among intersections. Agents were trained using the Proximal Policy Optimization (PPO) algorithm within the SUMO simulator, using IoT-like sensors to capture dynamic traffic and pedestrian data. Cooperative learning mechanisms minimized congestion, waiting times, and pedestrian delays. Simulation results demonstrate that the VLC-enhanced O-IoT system reduces average queue lengths by up to 23% and improves pedestrian flow by 18%, outperforming centralized approaches. The proposed framework demonstrates how optical wireless communication can enable scalable, adaptive, and resilient traffic systems, supporting the development of intelligent and sustainable smart cities.