A universal model about the sufficient condition of stable single-longitudinal-mode (SLM) operation is established and applied to the theoretical analysis of a high power unidirectional ring Nd:YVO laser at 1342 nm with energy transfer upconversion and excited stimulated absorption taken into account. A stable continuous-wave SLM laser with 1342 nm power of 11.3 W and 671 nm power of 0.3 W is fabricated by optimizing the transmission of output coupler and the temperature of LiB3O5 crystal. Mode-hopping-free laser operation with a power stability better than ± 0.5% and a frequency fluctuation less than ± 88 MHz is achieved during a given three hours.

A self-consistent theoretical model considering both energy-transfer upconversion (ETU) and excited-state absorption (ESA) effects, as well as the couplings among the temperature distribution in the laser crystal, the thermal fractional loading, the upper state population involved in the ETU and ESA effects, the laser output and other temperature-dependent parameters, was developed to simulate the behaviors of diode-end-pumped continuous-wave (CW) single-transverse-mode (TEM) lasers. Based on the theoretical and experimental investigations of the influences of ETU and ESA effects on laser performance, a high power CW TEM Nd:YVO 1.34 μm laser dual-end pumped at 880 nm was achieved with a maximum output power of 16 W. The measured laser beam quality was M = M = 1.17 and the stability of the laser output was better than ± 0.9% in a given four hours. The theoretical predictions considering both ETU and ESA effects are in good agreement with experimental results.

Hyperspectral imaging technology can obtain the spatial information and spectral information of the simulated operational background and its camouflage materials at the same time and identify and classify them according to their differences. In this paper, we collected the hyperspectral images (400–1000 nm) of the desert background, jungle background, desert camouflage netting, jungle camouflage netting, and jungle camouflage clothing through the hyperspectral imaging system, and the samples were preprocessed by denoising and black-and-white correction. Then, we analysed the region of interest (ROI) of the training samples by principal component analysis (PCA). After the pixels in the region of interest and their surrounding areas were averaged, 60% of the data was used as the training samples, and the remaining 40% was used as the test samples. According to their similarities and differences between them and referenced spectrum, the models of classification were established by combining the Naive Bayes (NB) algorithm, K-nearest neighbour (KNN) algorithm, random forest (RF) algorithm, and support vector machine (SVM) algorithm. The results show that among the four models, SVM model has the highest accuracy of classification and the recognition rate of jungle camouflage clothing is the highest. This study verifies the scientific and feasibility of hyperspectral imaging technology for camouflage identification and classification in a simulated operational environment, which has some practical significance.

According to the principle of phase-shifting interferometry and spiral phase characteristics of the vortex beam, this article proposes a method for detecting the surface profile of a transparent object, in which the +1 order vortex beam is generated by a spatial light modulator and is taken as the reference light. The influence of the nonlinear phase modulation characteristics of the spatial light modulator on the measurement precision is studied. The results show that nonlinear phase modulation has a great impact on the measurement. Then, the vortex lights with initial phases of 0, π/2, π, and 3π/2 are used to measure the H-type thin film sample based on the Twyman-Green interference system after correcting the nonlinear phase modulation characteristics. The experimental results show that the measurement error of the surface profile to an object with the theoretical value of 20 nm is 1.146 nm, and the feasibility of the optical vortex phase-shifting technique used to measure the surface profile of an object is verified.

One of the most important goals of research on three-dimensional nonscanning laser imaging systems is the improvement of the illumination system. In this paper, a new three-dimensional nonscanning laser imaging system based on the illumination pattern of a point-light-source array is proposed. This array is obtained using a fiber array connected to a laser array with each unit laser having independent control circuits. This system uses a point-to-point imaging process, which is realized using the exact corresponding optical relationship between the point-light-source array and a linear-mode avalanche photodiode array detector. The complete working process of this system is explained in detail, and the mathematical model of this system containing four equations is established. A simulated contrast experiment and two real contrast experiments which use the simplified setup without a laser array are performed. The final results demonstrate that unlike a conventional three-dimensional nonscanning laser imaging system, the proposed system meets all the requirements of an eligible illumination system. Finally, the imaging performance of this system is analyzed under defocusing situations, and analytical results show that the system has good defocusing robustness and can be easily adjusted in real applications.