Applied Physics B最新文献

We present a longitudinally diode-pumped Q-switched Nd:YAG/V:YAG microchip laser emitting at (1.44,upmu)m and the optimization of its output parameters in terms of pulse energy and peak power maximization. Optimization was achieved by modifying the size of the pumping beam with four compact focusing systems, each consisting of an aspheric collimator and one of four aspheric focusing lenses. The laser’s emission spectrum, average power, pulse duration, and spatial beam profile were measured for pumping repetition frequencies ranging from 10 to 715 Hz. Using different focusing systems, it was possible to increase the maximum pulse energy and peak power up to (91,upmu)J and 14.8 kW, respectively. Thermal effects due to pumping influenced both the laser operation and the parameters of the V:YAG saturable absorber, leading to a decrease in pulse duration from 9.6 to 4.9 ns.

The combination of the “2 + 1” phase-shifting algorithm with temporal phase unwrapping (TPU) not only facilitates the acquisition of phase information using fewer fringe patterns but also minimizes errors resulting from motion in the 3-step phase-shifting profilometry (PSP). By considering the influence of fringe frequency sequences on measurement accuracy, we derive the noise-induced wrapped phase error and its variance of the “2 + 1” phase-shifting algorithm and further analyze the phase unwrapping accuracy at each stage of the “2 + 1 + 2 + 2” algorithm. Consequently, a method for selecting the optimal fringe frequency sequence is introduced, ensuring that the phase unwrapping accuracy in both stages remains as consistent as possible, while the effectiveness of this method is experimentally validated. The experimental results demonstrate that the method for selecting the optimal fringe frequency is applicable to both hierarchical and heterodyne TPU and aligns well with theoretical analysis. Compared to two sets of non-optimal frequency sequences, the error rates of the optimal fringe frequency sequences are reduced by 33.41% and 72.53%, respectively.

In this work we present the power scaling of diode-pumped waveguide lasers fabricated in a Pr:LiLuF₄ crystal by direct femtosecond writing. We demonstrated a maximum output power of 360 mW at 604 nm, 420 mW at 721 nm, and 55 mW at 523 nm. Moreover, we demonstrated what we believe to be the first operation of a waveguide laser at 545 nm. In the end, we achieved stable lasing at 604 nm with an extraction of 96%, demonstrating the high gain achievable in waveguide devices.

A temperature-compensated magnetic field sensor based on a hollow core Bragg fiber (HCBF) Fabry-Perot interferometer (FPI) is proposed. The two ends of the HCBF are fused with optical single-mode fibers (SMF) and adhered to magnetostrictive rods. The temperature and magnetic field response can be demodulated by 2 × 2 sensitivity matrix method, achieving multiparametric demodulation of dual parameters. Experimental results indicate that the error rate of demodulated magnetic field is only 1.9%, while the error rate of demodulated temperature is only 0.8%. The ease of fabrication, high accuracy and temperature compensation suggest that the proposed fiber sensor is suitable for practical magnetic field sensing applications.

The performance of QKD systems in airborne environments is significantly hindered by optical distortions and perturbations caused by the boundary layer around high-speed aircraft. This paper proposes an optimization scheme to enhance airborne QKD system performance by analyzing the flow field around the transmitter and strategically positioning it under specific flow conditions. Using ray tracing and two distinct airborne QKD models, we evaluate system performance across various installation positions. Our results show that the largest beam deflection occurs when the transmitter is placed at the center of the wing in air-to-ground scenarios, while the QBER remains consistent across different wing positions, indicating minimal boundary layer effects on QBER. In air-to-air scenarios, optimizing the quantum source placement reduces the photon offset by 6.3 m, with QBER consistently measured at 6% ± 1% across wing positions. These findings offer critical insights for the design and deployment of QKD systems in practical airborne applications.

An image encryption algorithm enhances the security of an image by transforming its content into a scrambled format. This process employs mathematical techniques, including chaos theory, permutation, and diffusion, to prevent unauthorized access or tampering. To improve the security of images during transmission, we introduce an efficient and innovative image encryption algorithm based on a time-delay predator–prey model, integrating principles from ecological dynamics into cryptography. By appropriately selecting parameters of the proposed predator–prey model, chaotic phenomena are generated. We use these chaotic sequences for image encryption and combine them with the Arnold scrambling algorithm to rearrange pixel positions within the image. Additionally, a diffusion algorithm is employed to alter pixel values, achieving the encryption effect. Various experimental analyses, such as initial value sensitivity, histogram analysis, adjacent pixel correlation, and overall robustness evaluations, are conducted. The computational experiments indicate that the chaotic sequence generated by the proposed predator–prey model can effectively implement image encryption with a favorable encryption effect. We present the results of the model on the best Number of Pixel Change Rate (NPCR) and Unified Average Change Intensity (UACI) scores for various selected test images. In the end, the average NPCR and average UACI are 99.6067% and 33.4687% respectively. We also calculated the value of the information entropy indicator, which reaches 7.9986. Through these empirical validations, the numerical results highlight the robustness and viability of using chaotic sequences in the context of image encryption, offering promising prospects for enhancing data security in digital transmission systems.

The temperature dependence of the laser output properties of the Fe:ZnSe single crystal was compared under its excitation by 2.94 ({upmu })m Q-switched Er:YAG laser radiation and by (sim)4.04 ({upmu })m gain-switched second Fe:ZnSe laser radiation within the same semi-longitudinal configuration. A non-selective laser cavity consisted of a flat highly reflective mirror at (sim)4–5 ({upmu })m and a concave (r = 200 mm) output coupler with a reflectivity of 88% at (sim)3.9(-)5.3 ({upmu })m. To keep the energy at both excitation wavelengths the same of (sim)9.4 mJ, a special filters were used for attenuation of 2.94 ({upmu })m radiation. The output energy almost doubled since the angle between pumping and generated laser radiation was reduced from (sim)20(^{circ }) to (sim)12(^{circ }). The generated laser oscillation wavelength was shifted by (sim)100 nm in the case of (sim)4.04 ({upmu })m compared to excitation by 2.94 ({upmu })m radiation. The maximum laser output energy of (sim)1.7 mJ under 2.94 ({upmu })m excitation was obtained at 78 K. However, at (sim)4.04 ({upmu })m pumping, the maximum of (sim)0.5 mJ was obtained at 260 K. The efficiency at 2.94 ({upmu })m excitation decreased from (sim)33% at 78 K to (sim)12% at 340 K. At (sim)4.04 ({upmu })m radiation excitation, the efficiency increased from the laser threshold at 120 K to its maximum of (sim)9% at 260 K.

Considering the quantum memory channel, we investigate the connection between quantum correlation and coherence for correlated channels. Initially, various results were obtained by considering the action of noise channels on the initial state. The quantum correlation behavior does not increase by the quantum operation or by the action of noise channel. Similarly, coherence remains slow for various initial states under correlated channels. In this work, we observed the decrement of quantum correlation and coherence, which can be improved by choosing the initial state and by adjusting the parameters. Our results provide valuable insight into defining the robustness of the pure state in comparison with the mixed state under correlated channels, which offers practical solutions for quantum information processing task.

Higher-order Hermite–Gaussian modes, characterized by their intricate spatial distribution, are garnering significant interest in domains such as precision measurement and optical communication. This paper introduces a beam shaping method that integrates the Gerchberg–Saxton algorithm with a convolutional neural network to generate the higher-order modes. Employing this approach, we successfully generated various orders of Hermite–Gaussian modes and light fields with arbitrary intensity distribution. Furthermore, a comparative assessment was undertaken, contrasting the root mean square error of the generated modes against those obtained via the Gerchberg–Saxton algorithm. The results demonstrated that our method yields a closer match between the generated and target light fields, translating to superior beam quality. This study not only enhances the theoretical underpinnings of beam shaping technology but also opens up new avenues for the application of neural networks in optics.

The coherent transfer of optical vortices in a four-level double-cascade cold atomic ensemble is examined, showcasing the transfer of orbital angular momentum from the incident vortex probe field to the generated signal field through the four-wave mixing process. Results indicate that, without single-photon detuning, the transfer efficiency is limited to 25% under phase matching conditions. However, in the presence of single-photon detuning, the conversion efficiency of optical vortices between the probe and signal fields can be significantly increased. Interestingly, the presence of single-photon detuning can enhance, rather than diminish, the transfer efficiency of optical vortices. Furthermore, the impact of the control field on the composite vortex formed by the incident vortex probe and signal fields was investigated. Findings suggest that adjusting the strength of the control field allows for precise control over the strength and phase patterns of the composite vortex.