In the field of distributed optical fiber sensing technology, the application of the Brillouin scattering based optical time domain analysis system (BOTDA) in infrastructure structure health monitoring (SHM) has shown large-scale development, and the monitoring demand for the distribution of strain and temperature changes along or within engineering structures is increasing. The single-ended BOTDA system, with the convenient usage mode of single-end access of the sensing optical cable and combined with its own advantage of high-precision measurement, has won the favor in the engineering application field. In this paper, the development of single-ended stimulated Brillouin scattering fiber sensing technology is studied and summarized, the principle and characteristics of the single-ended BOTDA system based on Fresnel reflection and Rayleigh scattering are expounded, and the technical research of these two types of systems is subdivided, while the core content of each technical route is analyzed and discussed, such as heterodyne detection technology and multi-wavelength technology. Compared with the traditional double-ended access system, these types of single-ended BOTDA show different degrees of improvement in terms of simplifying the system structure, shortening the algorithm demodulation time, and reducing the frequency sweep times in addition to the advantages of single-ended access systems. Through the comprehensive analysis of related achievements and research progress, it is expected to further promote the in-depth research of high-performance single-ended BOTDA technology and its extended application in various related engineering fields.

Traditional remote sensing imaging for marine oil spills faces challenges such as high sensitivity to lighting conditions, low oil?water contrast, and significant surface glare interference. To address the resulting degradation in imaging quality and reduced accuracy of monitoring systems, this study employs four imaging modalities—visible light, visible light polarization, near-infrared, and long-wave infrared—to conduct outdoor field experiments under three high-interference scenarios (strong light, weak light, and sun glint conditions) from the perspective of oil spill imaging channel selection. By comparatively analyzing the information entropy and strong edge width of oil spill images across the four imaging modes, the study verifies the feasibility of using visible light polarization imaging under strong/weak light and sun glint conditions, and near-infrared imaging under strong light and sun glint conditions for oil spill detection. Meanwhile, experiments demonstrate that long-wave infrared exhibits limited effectiveness for thin oil film detection under weak illumination or sun glint conditions. This research provides experimental evidence for selecting optimal information channels in marine oil spill monitoring systems.

This research aims to provide a rapid, non-destructive solution for monitoring ionic liquid mass fraction in pharmaceutical production by proposing and validating a systematic chemometric modeling framework based on near-infrared (NIR) spectroscopy. The study first identifies 1350?1650 nm as the optimal analytical band through spectral mechanism analysis. Subsequently, based on the spectral data of 59 ionic liquid samples, the efficacy of various preprocessing and feature selection algorithms is systematically compared. Standard normal variate (SNV) is identified as the optimal preprocessing method, and competitive adaptive reweighted sampling (CARS) is determined to be the superior feature selection algorithm. The final SNV-CARS-PLSR quantitative model, integrated with partial least squares regression (PLSR), demonstrates excellent predictive performance: a root mean square error of calibration of 0.0689, a calibration determination coefficient of 0.9836, a root mean square error of prediction of 0.1008, and a prediction determination coefficient of 0.9666. To verify the universality of this methodological framework, it is further applied to a quantitative analysis of a glucose aqueous solution system, which also achieves outstanding prediction accuracy (0.9993). The systematic optimization strategy established in this study not only provides robust technical support for the real-time monitoring of ionic liquids but also offers a versatile methodological reference for the application of micro-NIR spectroscopy in the fine chemical industry.

To enhance the localization capability of Brillouin optical time-domain reflectometry (BOTDR) for weak temperature variations along optical fibers, a method based on Brillouin frequency shift (BFS) fluctuation calculation is proposed. This method uses the BFS of a temperature-invariant fiber as a baseline, which is processed via sliding averaging to establish a reference benchmark. The measured BFS data under temperature variation undergoes identical processing and is then compared pointwise with the benchmark. This enables the localization of weak frequency shift points and the inference of their corresponding temperature variation ranges. Experimental results demonstrate that, without adding any additional hardware components to the system, the proposed method successfully identifies minute temperature change regions of 0.5 ℃, leading to improved system performance.

This paper presents a method for suppressing parasitic oscillations in crystalline waveguides, resulting in actively Q-switched laser output with high peak power and high optical-to-optical efficiency. The structural optimization of the Yb∶YAG/Er∶YAG single-clad crystalline waveguide incorporates three key enhancements: first, a highly absorptive Ge infrared coating applied to the cladding surface absorbs amplified spontaneous emission (ASE) photons in the cladding, effectively blocking parasitic oscillation pathways; second, the implementation of a slight refractive index differential between core and cladding increases the critical angle for total internal reflection of ASE at the interface, thereby reducing the grazing angle and decreasing the number of ASE reflections to block the reflection path within the core; third, the incorporation of a 0.5° tilt angle at the crystalline waveguide end faces eliminates residual ASE end-face reflections. Experimental data demonstrates that with an absorbed pump power of 67 W, the actively Q-switched crystalline waveguide generates an average output power of 15 W, a pulse energy of 1.5 mJ@10 kHz, a pulse width of 10 ns, and a peak power of 150 kW, achieving an optical-to-optical efficiency of 22% and a dynamic-to-static ratio of 57.7%. The beam quality factors in the x and y directions are 1.15 and 1.10, respectively, which are better than those of the conventional crystalline waveguides. Additionally, the crystalline waveguide maintains consistent output power without saturation at high pump power, confirming the effectiveness of parasitic oscillation suppression. This methodology establishes a novel approach for designing Q-switched/mode-locked lasers utilizing crystalline waveguides, offering substantial applications in laser processing, remote sensing, and related fields.

This paper proposes a specular reflection-based normal estimation method that employs polarization imaging to separate surface reflections into specular and diffuse components, achieving high-precision normal imaging. The imaging transition model is explored, an optimal strategy to determine the normal angle is discussed, and based on this, an active normal field imaging system employing a polarized LED light source is built and calibrated. Experimental results show that our method can measure surface normals with an MSE<0.7 (°)2 in a range from -25° to 25°. This imaging system is applied to investigate 14 different types of art paper. The results reveal that this method can effectively capture the normal variation of surfaces with low sensitivity to paper color. It also offers insights for the identification and restoration of calligraphy, paintings, and cultural relics.

Exploring the distribution and state of resources in the lunar polar regions has become a hotspot in the current international lunar exploration field. China's Chang'e-8 mission requires in-situ infrared spectroscopic exploration of the lunar polar regions. However, the extreme environmental conditions in these areas such as low illumination and low temperatures pose numerous technical challenges for infrared spectroscopic detection. Regarding the current state of technology for in-situ spectral detection on the lunar surface, this paper specifically analyzes the major technical challenges faced in polar region exploration, and discusses potential solutions, aiming to offer theoretical and technical support for in-situ spectroscopic exploration of the lunar polar regions.