Search Results (1,077)

We report, for the first time, a continuous-wave (CW) switchable multi-wavelength Nd:Lu₂SiO₅ (Nd:LSO) laser using two wedge birefringent filters (WBFs) operating on the ⁴F_3/2 → ⁴I_13/2 transition. The threshold equivalence condition was calculated via the two intracavity WBFs to achieve the simultaneous multiple-wavelength operation. Three dual-wavelength pairs (1332/1344 nm, 1344/1359 nm, and 1359/1363 nm), two triple-wavelength combinations (1332/1344/1359 nm and 1344/1359/1363 nm), and a four-wavelength set (1332/1344/1359/1363 nm) were further experimentally demonstrated. These wavelength combinations are mutually switchable via tuning of the WBF. Under an incident pump power of 20 W at 808 nm, the total output powers for the dual-wavelength pairs (1332/1344 nm, 1344/1359 nm, and 1359/1363 nm) were measured to be 1.55 W, 2.17 W, and 3.40 W, respectively. The triple-wavelength outputs at 1332/1344/1359 nm and 1344/1359/1363 nm delivered 1.57 W and 1.91 W, respectively. The four-wavelength emission at 1332/1344/1359/1363 nm reached 913 mW. Full article

Accurate spot-centroid localization is fundamental for determining optical metrics such as modulation transfer function (MTF) and effective focal length (EFL). Conventional methods struggle under non-ideal conditions—asymmetric spots, high noise, and vibration—and mid-wave infrared (MWIR) vibration has received little attention. To address these gaps, we propose multi-scale Gaussian fitting with subpixel edge reconstruction (MSGF-SER), combining image pyramid fitting, Zernike-moment edge extraction, and adaptive eccentricity-weighted fusion. Validated on simulated spots with varying SNRs and experimental sequences (visible off-axis aberration, long-wave infrared (LWIR) high-noise, MWIR micro-vibration), MSGF-SER achieved a noise-free RMSE of 0.03 pixel and 0.84 pixel at 5 dB SNR. On real MWIR vibration sequences, the Y-direction standard deviation (STD) dropped to 0.098 pixel, and the trajectory displacement variance was more than an order of magnitude lower than that of conventional methods. MTF deviations remained within 0.01, and the deviation of the measured mean EFL from the nominal focal length was better than 0.05 mm, and the STD was below 0.02 mm. These results demonstrate that MSGF-SER substantially improves centroid localization accuracy, repeatability, and smoothness under challenging conditions, providing reliable support for high-precision optical system parameter measurement. Full article

Accurate nanoscale displacement readout is essential for optical inertial sensors, precision positioning, and micro-vibration characterization. In this work, we develop a free-space optical heterodyne interferometric readout system for low-frequency nanoscale displacement sensing and establish an SNR-guided adaptive demodulation framework. Two complementary demodulation strategies are integrated: Bessel-function-based frequency-domain sideband extraction for small-amplitude low-SNR motion and IQ quadrature phase tracking for larger-amplitude displacement. The experimentally demonstrated framework maps the applicability regimes of the two methods and enables wavelength-referenced displacement readout over a range from sub-nanometer narrowband detection to 250 nm under the present experimental conditions. The implemented system achieves a repeated-measurement repeatability of 0.40 nm under a 10 Hz excitation condition, and spectral SNR analysis is consistent with time-domain statistical evaluation. Finally, the readout system is applied to a quartz pendulum inertial structure, demonstrating its potential for photonic displacement sensing and optical inertial sensor characterization. Full article

Fluorescence emission-excitation matrices for cow milk samples with different fat contents in the range of 0.05–10% and a constant protein content of 3%, as well as for butter and extracted milk components such as casein and lactose, have been measured using a spectrofluorometer. The influence of the increased fat content on the shape of the fluorescence spectra of milk has been studied. In addition, fluorescence spectra measured for serial dilutions of high-fat milk with water and skim milk, along with aqueous dilutions of skim milk, have shown that the fluorescence diagnostics of fat and protein content in milk can be implemented using excitation at only two wavelengths: 280 and 320 nm. The optimal spectral ranges proposed for detecting the content of milk components via fluorescence measurements can be useful when designing UV LED-based fluorescence analyzers of milk composition. Full article

Surface-emitting distributed-feedback (SE-DFB) semiconductor lasers based on second-order gratings face a fundamental triple constraint: the spatial co-location of gain, grating feedback, and vertical radiation functions limits single-mode selectivity, surface extraction efficiency, and far-field beam quality simultaneously. We propose a quasi-parity-time (PT)-symmetric SE-DFB laser with separated gain and radiating-grating sections. In this design, the electrically injected gain section and the passive second-order grating section are placed in different regions along the cavity axis, thereby separating electrical injection from surface emission without epitaxial regrowth. Coupled-mode theory and two-dimensional finite-element simulations demonstrate that the resulting longitudinal non-Hermitian gain–loss asymmetry produces spatial-overlap-dependent threshold discrimination, enabling an isolated low-threshold lasing branch that remains separated from competing cavity modes over the investigated pump-parameter range. Under the HR–AR boundary condition, the proposed design achieves a threshold gain margin of $\mathsf{\Delta }g=12.4$${\mathrm{c}\mathrm{m}}^{-1}$, more than six times that of a conventional HR–AR DFB benchmark considered here, together with an upward surface extraction efficiency of 23.4% obtained from 2D FEM simulations. A simplified steady-state rate-equation estimate further suggests that the increased threshold margin can support strong side-mode suppression. The design imposes no regrowth requirement and is fully compatible with standard single-growth InP ridge-waveguide fabrication. Full article

Conductor on Round Core (CORC) high-temperature superconducting cables are critical for next-generation magnetic confinement fusion devices, yet their performance is highly sensitive to geometric variations, necessitating high-precision non-contact inspection. This study presents a laser triangulation measurement system that integrates an optical structural design scheme and a deep learning-based light-plane calibration method. For optical structural design, we established an imaging model incorporating thin-lens geometry and the Scheimpflug condition, formulated an objective function balancing minimum sensitivity and sensitivity stability, and employed a grid-search strategy under engineering constraints to determine optimal parameters. For calibration, we proposed a deep learning-based light-plane calibration method that predicts point-wise weights for laser point clouds extracted during the calibration process and incorporates them into weighted fitting to improve robustness against noise and outliers. Experimental results demonstrate that the optimized optical structure reduces system measurement error and error variation, while the proposed light-plane calibration method further improves measurement accuracy and repeatability. Together, these enhancements decreased system nonlinearity error from 0.079% to 0.064% compared to conventional settings. Engineering applicability was validated by comparing measured CORC cable diameters with precision micrometer references. The proposed framework may provide a methodological reference for the design and calibration of laser triangulation measurement systems under similar geometric configurations and engineering constraints. Full article

Dissolved gas analysis (DGA) is an essential technique for the fault diagnosis and condition monitoring of oil-immersed power transformers. Among various characteristic gases, acetylene (C₂H₂) is a key indicator of high-energy discharge and arc faults. In this work, a high-sensitivity dissolved acetylene detection system is developed based on clamp-type quartz-enhanced photoacoustic spectroscopy (QEPAS). A specially designed clamp-type quartz tuning fork (Clamp-type QTF) is employed as the acoustic transducer to improve acoustic coupling efficiency and optical alignment tolerance. Compared with conventional standard quartz tuning forks, the clamp-type structure exhibits enlarged acoustic interaction volume, lower damping loss, and higher signal collection capability. A near-infrared distributed feedback (DFB) laser operating at 1531.6 nm is used as the excitation source. The dissolved gas is extracted from transformer oil using a headspace degassing module and introduced into the QEPAS cell for real-time measurement. Experimental results showed that the developed system achieves a 1σ-based SNR-estimated detection limit of 17 ppb at a 50 s integration time, derived from the continuous measurement of 0.75 ppm C₂H₂, with excellent linearity in the concentration range from 100 ppm to 500 ppm. The measured concentration of dissolved acetylene in transformer oil is in good agreement with gas chromatography (GC), validating the effectiveness and practical applicability of the proposed system. Full article

The laser irradiation effect on Charge-Coupled Devices (CCDs) has attracted wide attention in photoelectric countermeasures and imaging system hardening. This review provides a systematic analysis of the phenomena and mechanisms of laser-induced dazzling and damage effects on CCD sensors. It summarizes experimental and theoretical research progress with continuous-wave (CW), pulsed, and composite lasers, revealing distinct interaction mechanisms such as thermal effects, dielectric breakdown, and plasma ablation. The review also covers quantitative evaluation methods for assessing laser irradiation effects. This work provides a comprehensive reference for future studies. Full article

To meet the demand for high-precision target classification in complex scenes, a hyperspectral–polarimetric–LiDAR multimodal image fusion method tailored for few-shot scenarios is proposed. Feature-mapping functions for polarimetric and LiDAR images are constructed, and a multi-scale hierarchical optimization strategy is employed to jointly enhance low- and high-frequency components across modalities. This approach effectively addresses key challenges under limited training data, such as substantial cross-modal dimensional disparities and the difficulty of robust feature extraction and fusion. The proposed algorithm conducts bimodal image fusion on the NWPUSP spectral-polarization dataset and KAIST spectral-depth dataset. Compared with other fusion methods, it achieves average increases of 7.3% and 4.87% in information entropy, 53.18% and 30.35% in standard deviation, 48% and 108.28% in average gradient, as well as 96.25% and 101.13% in spatial frequency, respectively. Moreover, relying on the self-developed integrated hyperspectral-polarization imaging system and commercial LiDAR, we synchronously and efficiently acquire multimodal images including hyperspectral, polarization and LiDAR images of complex ground object scenes. Comparative experiments are implemented against six other mainstream fusion algorithms. The objective evaluation results show that the average improvements reach 7.19% in information entropy, 46.85% in standard deviation, 76.62% in average gradient and 79.74% in spatial frequency, which notably enhances the feature retention capability of fused images. Under few-shot conditions, the target recognition classification accuracy and Kappa coefficient of the fused image are improved by 9.8% and 11.05%, respectively, compared with those of the unimodal hyperspectral image. This effectively highlights targets under shadow occlusion and compensates for LiDAR’s response deficiencies to surface textures, achieving complementary advantages of multimodal images for ground object targets in complex scenes. This research provides a new solution for future optical multimodal remote sensing and image fusion. Full article

The phenomenon of pulse tailing, primarily caused by relaxation oscillations, presents a significant challenge to increasing the repetition rates of gain-switched semiconductor lasers. This paper proposes a novel approach to mitigate this issue by simultaneously regulating both the magnitude and pulse width of the pump current, enabling stable, tail-free pulse generation across a broad range of repetition frequencies. Numerical solutions to the carrier rate equations are first employed to investigate the origins of optical pulse tailing. By reducing the current injection duration from 200 ps to 50 ps, carrier injection is effectively truncated, suppressing relaxation oscillations. However, this reduction also leads to a decrease in peak optical pulse power, limiting the laser’s applicability. Increasing the injection current’s magnitude provides a solution. Consequently, a high-precision circuit design has been developed to digitally adjust both the magnitude with a precision of ~3 μA and the pulse width with a resolution of 5 ps. This configuration successfully generates 200 ps optical pulses with a single-pulse energy of 0.96 pJ at 1550 nm, over a repetition rate range from 10 kHz to 1 GHz. With this laser as the transmitter, RZ-OOK modulated signal transmission at a slot rate of 250 MHz has been realized. The proposed scheme offers a stable, reliable optical emission source, making it ideal for high-speed, high-capacity optical time-division multiplexing communication, time-resolved spectroscopy, and laser ranging and imaging applications. Full article

Accurate measurements of wind fields in the troposphere and stratosphere are essential for advancing atmospheric dynamics research, improving weather prediction, and supporting aerospace operations. However, a single Doppler lidar technique usually has limited capability to provide vertically extended wind profiles across both aerosol-rich lower altitudes and molecular-dominated higher altitudes. In this paper, we present a hybrid Doppler lidar system that combines a 355 nm scanning incoherent Rayleigh Doppler lidar with a 1550 nm coherent aerosol Doppler lidar for multi-scale wind field detection. The coherent Doppler lidar is used for boundary-layer wind retrievals, while the Rayleigh Doppler lidar, based on the double-edge technique, extends wind profiling from the upper boundary layer to approximately 40 km. Field deployments demonstrate continuous wind profiling from 50 m to 40 km, extending from the boundary layer to the stratosphere. Comparisons with radiosonde measurements show good agreement during the field campaigns, supporting the feasibility of this hybrid configuration for vertically extended wind profiling. The resulting high-resolution wind measurements across multiple atmospheric regions provide valuable data sources for studies of multi-scale circulation research, gravity wave dynamics, and climate-related atmospheric processes. Full article

Medical lasers are a heterogeneous class of interventional and therapeutic devices. They are differentiated based on their active gain medium, which includes solid-state, gaseous, dye, and semiconductor (diode) formulations. The present article undertakes a systematic evaluation and synthesis of the findings from a reproducible dataset. The present study yields novel scientific results, including a four-level classification of medical lasers that considers the chemical formula for each type of gain medium. In addition, a multisided systemic analysis of the engineering application of medical lasers in clinical practice is conducted, including an analysis of the main engineering challenges as a structured framework. Furthermore, a clustering of engineering applications for medical lasers in 2025 is performed, and a quantitative landscape of medical lasers by variables is presented. The following variables are analyzed: wavelength (nm), power (W)/irradiance (W/cm²), fluence (J/cm²), and exposure time/pulse duration. The objective is to create a year-by-year “trend analysis” for future engineering opportunities (2026–2030). The structure of the article is logical and roughly follows the IMRAD structure, and a thread of argumentation is demonstrated. Full article

In this work, an adaptive Hartmann–Shack wavefront sensor (AHSS) is proposed, designed, and evaluated. This sensor allows for the modification in the dynamic range of wavefront aberration measurement, defined as the range between the minimum and maximum aberration value that can be measured with the sensor. This capability makes it suitable for studying optical aberrations in both objective systems and the human eye. AHSS consists of sixteen phase profiles corresponding to microlens arrays designed to be projected (one at a time) onto a spatial light modulator (SLM). In each design, the microlens size and focal distance parameters were varied. A calibration process was conducted, and aberration measurements were made in both artificial and real eyes. The results demonstrate good correspondence between the measurements with the AHSS and a conventional Hartmann–Shack sensor, which uses an actual refractive microlens array with fixed size and focal length parameters, proving their feasibility for measuring optical aberrations. The AHSS opens up possibilities for measurements in eyes with special characteristics, such as high aberrations, and enables the implementation of active optics aberration correction systems without the need for an additional refractive (physically lensed) wavefront sensor. Full article

Certain radiative processes have their characteristics, such as spectrum, spatial distribution or yield, modified by the medium in which they are generated. Such media are referred to as structurally active media. This article examines some of these processes, such as fluorescence, Raman scattering and the Cerenkov effect in the X-UV range. The active media considered are periodic structures capable of producing Laue–Bragg diffraction; the phenomena involved are the Purcell–Kleppner effect, Kossel diffraction, the anomalous Lamb effect and the Bragg–Raman and Bragg–Cerenkov effects. Full article

To overcome the limited high-temperature capability of silica-based fiber Bragg gratings (FBGs) and the accuracy degradation of gold-coated FBGs induced by residual stress, a temperature sensor based on a gold-coated FBG with high-temperature alloy packaging is proposed and fabricated. By introducing a high-temperature annealing pretreatment to the gold-coated fiber, residual stress is effectively relieved, enabling high-precision temperature measurement in high-temperature environments. Within the range of 20–800 °C, the annealed sensor achieves an accuracy of 0.72% F.S., a sensitivity of 9.65 pm/°C, and a linearity of 0.9997, in close agreement with theoretical predictions. After ambient vibration and high-temperature thermo-vibration tests, the maximum center wavelength shifts are 13 pm and 46 pm, corresponding to temperature variations of approximately 1.35 °C@24 °C and 4.77 °C@800 °C. These results demonstrate stable sensor performance under high-temperature testing conditions. In addition, a fitting formula applicable to different center wavelengths is proposed, significantly reducing calibration effort. The sensor features a simple structure, easy installation, and reliable performance, providing an effective solution for temperature sensing in extreme environments. Full article