Applied Physics B最新文献

A corner cube retroreflector (CCR) laser boasts an exceptional anti-misalignment property, and the limiting incident angle of the CCR determines its anti-misalignment capabilities. To facilitate an efficient analysis of the limiting incident angle of a CCR, we present an analytical expression for its three side reflection angles. Subsequently, we analyze the anti-misalignment limiting incident angle of the CCR, considering its bottom surface shape and refractive index. Theoretical analysis and simulation results indicate that when the refractive index (n₁) ≥ 1.22, the larger the value of n₁, the larger the limiting incident angle. When n₁ ≥ 2.175, the refractive index is no longer a limiting factor for the limiting incident angle. Furthermore, for the bottom surface shape of the CCR, the smaller the height–radius ratio of the CCR, the larger the limiting incident angle allowed by the CCR, which results in better anti-misalignment capability. This study provides a concise and efficient model for analyzing the anti-misalignment ability of the CCR. Additionally, it establishes a theoretical foundation for calculating the limiting incident angle of the CCR when dealing with incident light featuring a small optical field diameter.

In this paper, we present a high-efficiency dual-diode-pumped Tm:LGGG disordered crystal laser using in-band pumping architecture for the first time. The room-temperature absorption and emission spectral properties of the Tm:LGGG crystal were characterized across the spectral rang of 1500–2300 nm. A maximum output power of 11.5 W and a slope efficiency of 57.1% concerning absorbed pump power were achieved in continuous-wave regime. Moreover, the beam quality factor M2 was estimated to be 1.9 at above output power. In the acousto-optically Q-switching regime at a repetition rate of 1 kHz, a pulse energy of 5.71 mJ and a pulse width of 102 ns were achieved, resulting in a peak power of 55.98 kW.

The paper investigates the degradation of beam quality in spectral beam combining (SBC) systems with dual-gratings caused by defects in diode laser arrays (DLAs), focusing on the combined effects of beam linewidth, divergence angle, and beam deflection. A comprehensive model is developed to analyze how these defects affect the wavelength-locking mechanism and beam propagation, thereby degrading the output beam characteristics. The results reveal that the dual-grating configuration effectively mitigates angular broadening induced by linewidth dispersion. A linewidth of 1 nm results in a mere 8% reduction in the peak intensity of the combined beam, concomitantly leading to a 0.5 increase in the β factor. Although beam divergence exacerbates the degradation of beam quality, beam deflection is the dominant factor. A deflection angle of 3 mrad results in a 38% reduction in peak intensity and a 2.6 increase in the β factor, underscoring the necessity of controlling beam deflection. We hope this work provides critical insights into the interplay between DLA imperfections and SBC performance, offering a theoretical foundation for optimizing high-power, near-diffraction-limited beam combining systems.

In the framework of the Argon Power Cycle, millisecond-pulsed hydrogen gas injections into a high-pressure, room temperature nitrogen or argon ambient are investigated. Instantaneous Rayleigh scattering is used to quantify the hydrogen mole fraction in the ensuing jets. A readily available HDEV injector with a straight 0.55-mm orifice and an inward-moving needle controls the mass flow into the constant-volume setup in accordance with (compressible) choked flow theory. The linear dependence of the Rayleigh signal on the number density is experimentally validated and the validity for the assumed constant number density throughout the mixing jet is presented. The evolution of mole fraction is presented for both nitrogen and argon ambient gases, and pressure ratios of 2.5 and 10. Quasi-steady behavior is shown in both axial and radial direction, while self-similar behavior is already observed 3 mm from the nozzle ((x/d_textrm{e} = 5.5)).

Cylindrical shells, such as gas pipes and wind turbine towers, are common structural components. Ensuring the stability of these structures necessitates accurate measurement of their three-dimensional (3D) operating deflection shapes (ODSs). Laser Doppler Vibrometry (LDV) and Digital Image Correlation (DIC) are two prevalent optical measurement techniques. Measuring radial vibrations of a cylindrical shell only using a 1D scanning laser Doppler vibrometer (1D-SLDV) poses a challenging yet practical problem, as the cost of a 1D-SLDV is significantly lower than that of a 3D-SLDV. Addressing this issue, the authors previously proposed a scheme for measuring radial ODSs of a cylinder via mono-laser scanning. By leveraging the geometric relationship, the displacements measured by the laser at each point are transformed to obtain radial displacements. Although it was proven through numerical simulation using the finite element (FE) method, experimental validation via 3D measurements is critical and still pending. To ensure the reliability of this scheme, it is experimentally validated in this study through comparison with the actual radial ODSs captured by 3D DIC. To validate the accuracy of the corrected radial ODSs, the cosine similarity (CS) values across the radial ODSs obtained through the FE method, LDV, and DIC are calculated, demonstrating a high degree of similarity. Particularly, the LDV and DIC yield consistent radial ODSs, with their CSs exceeding 95% for each excitation frequency.

High-average-power, megawatt-peak-power solid-state lasers with high beam quality have garnered significant attention in the field of laser cleaning applications. This paper presents a 1064 nm diode-pumped Nd: YAG master oscillator power amplifier (MOPA) system employing a multi-mode stable resonator. The designed resonator exhibits minimal beam quality variation when operating in the second stability zone, combining excellent power scalability with remarkable multi-mode stability. A flexible beam delivery system incorporating a 400-µm-core-diameter optical fiber demonstrates exceptional performance, achieving coupling efficiency exceeding 95% at a maximum average output power of 701 W with 20 kHz repetition frequency. Furthermore, it reaches a peak power of 1.0 MW at 12 kHz repetition frequency while maintaining 588 W average power output. Experimental results confirm that this innovative design successfully balances high-power operation with beam quality preservation and efficient energy transmission.

We report a sensitive laser absorption diagnostic method for shock tube experiments using a multipass configuration with a single-line spot pattern. The multipass setup consists of two silver-coated concave mirrors, which are placed outside the optical windows of the shock tube. The multipass configuration increases the effective path length by a factor of 31. All the reflected beams are aligned within a single plane that is perpendicular to the propagation direction of the shock wave, mitigating the Schlieren and beam steering effects. We validated the approach by measuring shock-heated gases behind reflected shock waves using tunable laser absorption spectroscopy of water vapor at 7447.48 cm^− 1. Our approach enables sensitive species detection for high-temperature shock tube/laser absorption experiments.

In discrete variable quantum key distribution (DV-QKD), the homodyne detection method is frequently employed for its simplicity in use, effectiveness in terms of error correction, and suitability with contemporary optical communication systems. Being a coherent detection method, it relies on a local oscillator whose frequency is matched to that of the transmitted carrier’s signal. In this paper, we evaluate a free space optical (FSO) DV-QKD system based on the KMB09 protocol using Homodyne detection under random phase fluctuation and depolarizing noise error. We present simulation results for system efficiency and quantum bit error rate (QBER) for the proposed model. An obtained efficiency ((25%)) for our proposed DV-QKD system model shows that under atmospheric turbulence and noise effect and it is in line with the available analytical results. However, the inclusion of random phase fluctuation and noise led to higher-than-normal QBER which is anticipated in a real-world scenario.

This study investigates the influence of amplified spontaneous emission (ASE) on the output characteristics of a Master Oscillator Power Amplifier (MOPA) system, with particular attention to the temporal dependence of the signal-to-noise ratio (SNR). The time delay between the ASE generated in the power amplifier and the laser pulse emitted by the master oscillator was varied over a wide range, from − 36 to + 24 ns. A positive delay corresponds to the input signal entering the amplifier before the onset of ASE. Temporal profiles of the ASE, the input pulse, and the amplified output signal were recorded and analyzed. The results demonstrate that the temporal alignment of the input signal with the leading edge of the ASE critically affects the output power and the efficiency of population inversion utilization. The maximum output power of 3.87 watts was achieved at a time delay of plus 4.7 ns, when the peak of the input pulse coincided with the ASE front. Quantitative estimates of the ASE contribution to the output signal were obtained, enabling an assessment of the SNR under various timing conditions. These findings provide practical recommendations for optimizing synchronization in MOPA-based laser systems to maximize output contrast and minimize noise.