To address metastability, phase misalignment, and wavelength jumps in the high-frequency heterodyne interferometric measurement of computer numerical control (CNC) machine tool positioning errors, a robust all-hardware field-programmable gate array (FPGA) phase demodulation system is developed. The architecture adopts an all-hardware design covering the complete process from signal preprocessing to synchronous data alignment. The front-end integrates time-domain constraints and multi-stage convergence to filter noise and suppress metastability. The core layer utilizes a wide-threshold hysteresis algorithm with a quarter-cycle buffer to eliminate counting errors at the fundamental level. The back-end employs synchronous latching and handshake protocols for precise data alignment. Experiments conducted on a 3.2 m guide rail demonstrate that the average repeatability of the proposed system reaches 0.59µm, outperforming the Renishaw XL-80 (0.88µm), and the nonlinear residuals of both systems exhibit high consistency. Stability tests over a 1.5 m long-distance open path further confirm that the raw fluctuations of the system remain at the sub-micrometer level, with no phase-locking failures or jumps. This timing-deterministic, jump-free hardware solution offers significant potential for precision measurement in complex industrial environments.

The geosynchronous orbit (GEO) region hosts critical high-value satellites, making continuous space situational awareness essential for collision risk assessment and national security. We propose a model for quantitatively evaluating the performance and gain of ground-based optical telescope networks for GEO observation, with emphasis on key metrics including spatiotemporal coverage, system sensitivity, and detection latency for single and multiple stations. This framework supports flexible adjustment of site coordinates, sky background, telescope aperture, detector characteristics, and observational conditions, which provides decision-oriented data support for global network deployment and resource allocation. Validated against Stellarium simulations, the model demonstrates a mean spatial coverage error of 0.49% with high geometric accuracy. Brightness prediction errors below 1.0 magnitude relative to measured data confirm its feasibility and numerical stability. Combined with a two-facet model, the framework enables albedo-area retrieval of unresolved GEO targets, specifically for three-axis-stabilized satellites.

This study investigated the effect of laser pulse width on the laser-induced damage threshold of a CMOS photodetector with fs-ns laser pulsed width arranged by using the two-temperature model (TTM) and Fourier heat transfer models, and experimental verification was conducted. The simulated results show that for pulse widths 10ps<τ<100ps, both the TTM model and the Fourier heat conduction model are used. In the transition regime, the TTM is adopted for pulse widths shorter than 60 ps, and the Fourier heat conduction model is adopted for pulse widths larger than 60 ps. Over the investigated pulse width range of 50 fs to 300 ns, the thermal damage threshold of the CMOS photodetector is increased with laser pulse width. By accounting for thermal diffusion effects, the fitted scaling law is obtained as Fth∼τ[0.41]. To validate the simulated results, the laser-induced damage experiments of the CMOS photodetector are performed using 50 fs and 10 ns pulsed lasers and the results compared with existing research. The experimental damage thresholds agree with the theoretical predictions and the proposed laser-induced damage threshold-pulse width scaling law by accounting the wavelength-specific material parameters. This work provides theoretical support for assessing and mitigating laser-induced damage in the CMOS photodetector.

Stray light is primarily induced by internal reflections and scattering from off-axis radiation, surface scratches or particulate contamination on optical elements, and imperfections in diffraction gratings. It produces nonphysical distortions in measured spectra and radiometric quantities and is therefore a major contributor to the measurement uncertainty of imaging spectrometers. Because an imaging spectrometer simultaneously records two-dimensional responses, namely the spectral and spatial dimensions, both dimensions should be characterized and corrected in a consistent manner. In current practice, however, spectral domain and spatial domain stray light are often measured and corrected separately using different instruments and methodologies. This not only increases experimental complexity and testing workload, but more critically, the two calibrations are frequently performed using different targets and different radiance levels. The resulting mismatch in response magnitude between the spectral and spatial domains can undermine the accuracy and physical validity of the derived two-dimensional correction coefficients. To address this issue, this study proposes a two-dimensional synchronous stray light detection and joint correction method for imaging spectrometers and develops a dedicated synchronous measurement platform. Under a single experimental configuration, the same target is measured at the same response level to acquire both spectral and spatial stray light responses. A two-dimensional stray light correction matrix is then constructed and applied for pixel level joint correction. In parallel, optical mechanical stray light simulations are performed using a stray light analysis tool to verify the consistency of the underlying mechanisms and to cross-validate the experimental results. The measurements yield stray light coefficients of 0.02% in the spectral dimension and 0.05% in the spatial dimension, and the spatial domain result is consistent in order of magnitude with the two-dimensional simulation outcome of 0.013%, demonstrating the effectiveness of the proposed synchronous detection approach. After applying the spatial domain correction, the stray light coefficient is reduced to 0.012%, representing an improvement by a factor of 4.5 compared with the pre-correction level, which further confirms the effectiveness of the proposed two-dimensional synchronous stray light correction method.

Off-axis telescopes in operational states are susceptible to environmental variations and mechanical vibrations, which deviate the secondary mirror (SM) from its nominal positions and induce misalignment aberrations. Existing compensation techniques for SM misalignment-induced aberrations of off-axis telescopes typically rely on fixed multi-field points wavefront sensing data or spot images to solve for misalignment restoration solutions. These methods suffer from limitations such as poor environmental adaptability, inflexible field-of-view configuration, and high computational costs for achieving high-precision misalignment restoration solutions. To address this, this paper proposes an aberration compensation technique based on feature extraction and optimization from arbitrary single field point spot images. It utilizes unbiased finite impulse response (UFIR) moments to extract spot image features and combines them with the differential evolution (DE) nonlinear optimization algorithm to find equivalent misalignments, thereby achieving system aberration compensation. Simulation verifies the feasibility of this method and compares its performance with typical image moment approaches. The influence of atmospheric turbulence on the presented method is also analyzed. Finally, physical experiments are conducted on an experimental platform for further validation. This technique compensates for aberrations using only arbitrary single field point spot images, without requiring multiple field points wavefront or spot data, nor precise determination of actual misalignments. It simplifies the misalignment-induced aberration compensation process and provides a reference for subsequent engineering applications.

Accurate repair or compensation of buried multilayer phase defects in extreme ultraviolet (EUV) lithography requires reliable knowledge of their three-dimensional morphology, yet the bottom-profile parameters remain difficult to recover from a single aerial-image observation. Through controlled diagnostic simulations, we show that this limitation originates primarily from the observation rather than from insufficient network capacity: the aerial image is much more sensitive to the defect top profile than to the buried bottom profile, and the error therefore saturates even when the network is trained only on the bottom parameters. We address this information bottleneck by reformulating reconstruction as a conditional inverse problem in which the independently measurable top profile, physically coupled to the bottom through multilayer deposition smoothing, is used as an explicit prior. The resulting dual-stream network, CoPriNet, injects the prior into hierarchical image features through latent-conditioned feature-wise linear modulation and enforces the deposition-smoothing inequality by construction. On simulated EUV mask phase defects, CoPriNet reduces the bottom-parameter mean relative error to 0.91% for bump defects and 0.79% for pit defects, while remaining robust to noise in the reconstructed complex field and to moderate top-prior error.

The lack of a comprehensive global model for atmospheric attenuation remains a bottleneck in the operational planning and link budgeting of satellite-Earth free-space optical (FSO) communication links. Using 10 years of reanalysis and satellite data, we develop a global statistical model that accounts for uncertainties and hourly variability in liquid cloud, ice cloud, and aerosol attenuation. While liquid cloud attenuation is well described globally by a gamma distribution, ice cloud attenuation follows a log-normal distribution in the tropics and a gamma distribution in extratropical and polar regions. Aerosol attenuation follows a gamma distribution over oceans and a log-normal distribution over land. Though aerosol attenuation is generally an order of magnitude lower than cloud attenuation, it is shown to be crucial in locations with low cloud water and ice content. These findings provide a quantitative framework for the site selection of optical ground stations and link-budget studies of satellite-Earth FSO links.

We report on a polarization-maintaining (PM) very large mode area (VLMA) Er-doped fiber with a 40 µm hexagonal core, fabricated via the REPUSIL powder process. The fiber's performance was evaluated in a MOPA configuration under 976 nm cladding-pumping and 1480 nm core-pumping. A numerical model, distinguishing between isolated ions and clusters to account for cooperative up-conversion and pair-induced quenching, shows excellent agreement with experimental results. This validated model provides a robust tool for designing high-energy, eye-safe PM-VLMA fiber amplifiers.

A D-shaped photonic quasi-crystal fiber (PQF) surface plasmon resonance (SPR) sensor is numerically designed and analyzed. By patterning a silver-titanium dioxide (Ag-TiO2) composite film into a grating structure, the localized surface plasmon resonance (LSPR) is enhanced and the full width at half-maximum (FWHM) is narrowed. The finite element method (FEM) is employed to optimize the structural parameters. In the refractive index (RI) range of 1.36-1.425, the sensor obtained a wavelength sensitivity of 15,800 nm/RIU and a maximum figure of merit (FOM) of 929.02RIU[-1]. A maximum amplitude sensitivity (AS) of 11,709.8RIU[-1] is also obtained. With its excellent FOM and AS, the proposed sensor holds great application potential in chemistry, biomedicine, and environmental monitoring. These results demonstrate a promising strategy for designing high-performance SPR RI sensors.

Optical lens design based on an ideal point-source mathematical model suffers from performance degradation as the source size increases. In practical engineering applications involving extended LED sources, this results in issues such as poor irradiance uniformity and significant edge diffusion. To address this issue, we propose an extended-source light distribution design method based on discrete point-source generatrix set envelope fitting and optimization. The extended source is first discretized into a series of ideal point sources. The outer envelope of a set of generatrix curves-each obtained from the exact mathematical model of a point source-is then extracted and fitted to serve as the generatrix of the initial structure. In the optimization process, the fitting coefficients are iteratively adjusted through a coordinated framework that integrates three program modules: the optimization routine, the envelope fitting and restoration routine for the initial structure generatrix, and the two-dimensional ray-tracing routine. When the optimization metric, namely the root-mean-square error of the irradiance distribution, falls below a prescribed threshold, the restored generatrix coordinate data are used to construct a 3D lens model suitable for extended-source light distribution, which is then validated through ray tracing. The validation results show that the irradiance uniformity is improved from 76.8% for the initial structure to 92.7% after optimization; the RMSE of the irradiance distribution decreases from 1.625 to 0.827; and the edge irradiance gradient increases from 0.27 to 0.45, indicating that the edge diffusion problem is effectively mitigated. Furthermore, the robustness of the proposed method is verified through comparisons with the optimization method in commercial software and engineering tolerance analysis.

Vortex beams are important for rotational Doppler velocimetry, but the influence of element beam quality degradation on coherently combined vortex beams remains insufficiently clarified. Based on a compact honeycomb phased-array geometry with the central channel closed, this work uses the surrounding 18 effective sub-apertures to form coherently combined vortex beams. A radial high-order-mode degradation model described by M[2] is introduced. The target vortex-mode purity ηl is defined by the normalized full complex-field overlap with the M[2]=1.0 reference vortex field. Unlike prior studies mainly focused on turbulence-induced OAM degradation, adaptive beam formation, or rotational Doppler velocimetry algorithms, this work isolates the transmitting-element beam-quality tolerance and quantifies its transfer to Doppler peak identifiability. The results show that ηl decreases from 1.000 at M[2]=1.0 to 0.0305 at M[2]=3.0, and this degradation further affects rotational Doppler velocimetry performance under turbulence propagation.

We present the design and realization of a new configuration, to our knowledge, for a Stokes channeled spectropolarimeter where the two high-order retarders in the system share the same thickness. We show experimental measurements made using this system and compare results with the standard 1:2 thickness ratio configuration. We also explore alternative calibration approaches that use different linear polarization angles than the 22.5° that has been almost exclusively employed in previous research. Finally, we evaluate measurement accuracy for various input light sources and introduce a simple method to calculate the spectral resolution of a channeled spectropolarimeter.

Image acquisition time in multiple-plane phase retrieval can be considerably reduced by replacing mechanical camera translations with equivalent virtual wave propagations at a fixed plane. This can be done by uploading digitized transfer functions at the Fourier plane of a 4f system to a high-speed digital micro-mirror device (DMD). While previous studies used DMDs with orthogonal mirror layouts, virtual wave propagations using alternative DMD models with diagonal mirror layouts that induce scaling distortion have yet to be demonstrated. Furthermore, the influence of the 4f system magnification on the virtual wave propagation remains unexplored. In this study, it was demonstrated that virtual wave propagations using a diagonal-mirror DMD in a 4f system with non-unity magnification fail to replicate the field obtained by manual camera translations. To resolve the discrepancy, a novel virtual wave propagation model, to our knowledge, based on Fourier analysis that accounts for both the magnification and scaling distortion, is proposed. A systematic calibration method to determine the compensating factors and misalignments is also presented. The proposed model was validated through simulations and experiments and provides a generalized framework for DMD-based phase retrieval regardless of the DMD mirror layout and 4f magnification.

Ammonia (NH3) emerges as a promising carbon-free, sustainable fuel, but its integration into technical combustion processes requires accurate, spatially, and temporally resolved diagnostics, obtained through non-invasive techniques like rotational coherent anti-Stokes Raman scattering (RCARS). However, the lack of spectroscopic data for ammonia-containing gas mixtures hinders its integration into advanced RCARS spectral models for data evaluation. In this study, we experimentally investigated the broadening effect of NH3 on the N2 S-branch Raman linewidths using the picosecond time-resolved RCARS technique. Experiments were conducted on N2-NH3 binary mixtures containing up to 50% NH3, at atmospheric pressure and temperatures up to 870 K close to the ammonia-air autoignition temperature. The peak intensities of the rotational spectrum of NH3 are weak compared with the N2 peak intensity and its rotational coherences decay more rapidly than those of N2, limiting the direct application of NH3-based RCARS diagnostics in the presence of intense scatterers and complicating its linewidths determination. Nevertheless, NH3 was found to induce significant broadening of the N2 Raman lines, which must be quantified to avoid diagnostic errors in RCARS. The magnitude of the S-branch Raman linewidth, obtained from the coherence decay time constant, increases linearly with NH3 concentration, indicating a more efficient collisional energy transfer in N2-NH3 compared to N2-N2 collisions. This behavior enables direct determination of N2-NH3 broadening coefficients, providing key spectroscopic parameters for RCARS spectral modeling. We further demonstrate that the inclusion of the newly determined linewidth data for nitrogen thermometry prevents temperature errors from inaccurate linewidth approximations. Thus, the obtained N2-NH3 broadening coefficients provide the spectroscopic basis for extending RCARS thermometry and species diagnostics to ammonia-fueled combustion and reactive flow environments.

Sensing technology relying on mid-infrared (MIR) waveguides has garnered considerable attention as it contains abundant molecular vibrational absorption bands and provides valuable spectroscopic information for biochemical sensing. In this paper, we show a simple ZnSe ridge waveguide platform for glucose detection achieved by a combination of O[5+] ion irradiation and precision diamond-blade dicing. This results in a waveguide that supports single-mode propagation with a propagation loss of 1.0 dB/cm at the wavelength of 4 µm. Glucose concentration can be quantitatively determined by monitoring the concentration-dependent propagation loss arising from the interaction between the evanescent field and the surrounding glucose solution. The experimental results show that the sensor has a good linear response in the glucose concentration range of 0-35 mM, and it has a high concentration sensitivity up to 0.0479dB⋅cm[-1]⋅mM[-1]. The suggested platform will bring together low loss, compact integration, and enhanced light-matter interaction, paving the way to various applications such as biochemical sensing in the MIR and miniaturized lab-on-a-chip systems.