Applied Physics B最新文献

In this work, three-dimensional (3D) diagnostics of the graphite tile surface elements in the dome region of the HL-2A divertor in both poloidal and toroidal directions were investigated using laser-induced breakdown spectroscopy (LIBS) technology under simulated HL-2A vacuum conditions. LIBS spectroscopic analysis revealed the presence of impurity elements such as Si, Cu, Ca, Al, Fe, Cr, Ni, and Mn on the graphite tile surface. Depth profile results of the impurity deposited layer on the shoulder part of graphite tile showed that Fe, Cr, Ni, and Mn emission intensities gradually decreased and disappeared with depth. The Si, Cu, Ca, and Al initially increased, then decreased, and eventually disappeared in the depth profile. Two-dimensional (2D) depth profile results of impurity elements in the poloidal direction showed significant asymmetry in impurity deposition within 70 mm of the shoulder and 20 mm from the top, and the impurity layer thickness on the shoulder greater than that on the top (approximately 5.7 μm vs. 3.1 μm). Further 3D imaging of the surface elements of the HL-2A divertor demonstrated strong asymmetry of impurity elements on the graphite tile surface in the poloidal direction, but no significant asymmetry was observed in the toroidal direction within 50 mm.

Laser-induced fluorescence (LIF) is a non-invasive optical diagnostics technique frequently used in reactive media to measure physical properties such as gas-phase species concentrations and temperature. It provides important information for understanding reaction and transport processes. For deriving detection schemes that provide selective and quantitative information, fluorescence spectra of the species of interest as well as potential interference sources must be simulated. LIFSim 4.0 is a modular software for simulating absorption, LIF excitation, and LIF emission spectra of NO, SiO, OH, and O₂ that also can be extended by the user to include other species. Line positions, line broadening, and collisional quenching are calculated based on spectroscopic data from literature. The code provides spectral analysis tools to interrogate and analyze sensitive spectral regions suitable for derivation of temperature from multi-line LIF measurements. The library includes fitting functions optimized for enhancing and accelerating the post-processing of stacked LIF images with varied excitation wavelength for temperature imaging and separation of the target LIF signal from broad-band or scattering background as well as tools for assessing the validity of results in non-ideal measurement situations.

In the presence of nitrite and an aqueous hydrochloric acid medium, sulfadiazine is diazonated to create an azo compound. With the chemical formula (E)-4-((3- (tert-butyl)-2-hydroxy-5-methoxyphenyl) diazenyl)-N-(pyrimidin-2-yl), the compound is a synthetic benzenesulfonamide. Characterization of the azo molecule is done using mass, FTIR, and ¹H and ¹³C NMR spectra. Azo compound structure is optimized using Density Functional Theory (DFT). This study examines the nonlinear optical (NLO) characteristics of the azo compound via the utilization of two visible, continuous wave (CW) laser beams. The nonlinear refractive index (NLRI) and the nonlinear absorption coefficient (NLAC) of the azo compound are estimated using diffraction patterns (DPs) and Z-scan and found equal to 5.38 × 10^–7 cm²/W and 2.03 × 10^–3 cm/W, respectively. The DPs are numerically simulated using the Fraunhofer approximation of the Fresnel-Kirchhoff integral with good accord compared to the experiment’s findings. The all-optical switching (AOS) behavior of the azo compound is examined under irradiation with 473 and 532 nm CW laser beams.

Apodized coupling gratings distributed feedback (AC-DFB) lasers have demonstrated their ability to achieve narrow linewidth. However, the detailed impacts of facet coatings and the structural parameters of apodized coupling gratings on the longitudinal spatial hole burning (LSHB) effect, along with comprehensive evaluations of how the LSHB influences linewidth and in-depth optimizations in AC-DFB lasers, have yet to be thoroughly investigated. In this study, we present the physical models for AC-DFB lasers and utilize numerical simulations to investigate the influences of facet coatings and the structural parameters of apodized grating on the LSHB effect. The promoted uniformity of photon density distribution of AC-DFB lasers is achieved through the rational design of the apodized grating coupling coefficient distribution and length, which effectively modulates the optical field of the lasers. The further thorough analysis of AC-DFB laser linewidth, considering the impact of the LSHB effect, demonstrates that optimization can reduce linewidth broadening caused by the LSHB by 80.9%, narrowing the linewidth to 43.4 kHz at 120 mA with HR-AR facet coating. This study provides valuable insights into the precise optimization of AC-DFB laser, contributing to improved narrow linewidth performance and supporting their application in high-speed optical communication systems.

This paper investigates experimental and numerical simulation methods for achieving frequency degeneracy in high-order modes with orthogonal polarization of a CW diode-pumped Nd: YAG laser. In isotropic crystals, weak phase anisotropy from factors like inhomogeneous dopant distribution can cause polarization eigenmode frequency splitting. While frequency degeneracy can be achieved in the fundamental transverse mode through spot detection and frequency analysis, higher-order modes exhibit more complex frequency characteristics, and their interaction with this mechanism remains unclear. This study explores the polarization eigenmode frequency degeneracy in higher-order modes (TEM₅,₀). By introducing two quarter-wave plates into the resonator, we achieve effective frequency control, leading to polarization frequency degeneracy. Experimentally, we focus on the high-order mode generated by an off-axis laser. The polarization state is successfully controlled by rotating the angles of two quarter-wave plates in the resonator. Consequently, a linearly polarized TEM_5,0 mode laser is produced, reaching a maximum polarization extinction ratio (PER) of 24.77 dB. To further understand this phenomenon, numerical simulations are conducted to analyze the mechanism of polarization frequency degeneracy. The results indicate that the initial phase difference between two polarization eigenmodes, caused by weak birefringence, can be effectively adjusted by fine-tuning orientations of the two quarter-wave plates in the cavity, thereby achieving polarization frequency degeneracy. This study presents a novel approach to polarization control for high-order mode laser.

This work investigates tunable emission in a continuous-wave Yb:KGW microchip-type solid-state laser utilizing an external cavity. While microchip lasers offer advantages like compactness and simplicity, achieving broad tunability within the compact laser structure presents challenges. The influence of crystal position relative to the pump on the emission polarization was explored. To achieve pump-independent tuning, two external cavity configurations were implemented, including a Littrow configuration with a diffraction grating and a configuration employing a bandpass filter. The filter-based configuration demonstrated superior performance, enabling a tuning range exceeding 35 nm. The obtained results demonstrate the potential of external cavity techniques to enhance the tunability and performance of microchip lasers for applications requiring wavelength-agile sources.

We reported an efficient continuous-wave (CW) and acousto-optically (AO) Q-switched Tm: LuAG laser at 2 μm in-band pumped by a 1.7-µm laser diode for the first time. A maximum CW output power of 7.26 W at 2013 nm was achieved with an incident pump power of 28.2 W, corresponding to a slope efficiency of 38.5% and optical efficiency of 25.6%. With a repetition rate of 1 kHz, a maximum pulse energy of 5.63 mJ and a minimum pulse width of 77 ns were achieved under AO Q-switching regime, corresponding to a calculating peak power of 73.1 kW. Moreover, the M²-factors in x- and y-directions were measured to be about 1.9 and 1.7 at maximum output power, respectively.

We investigate and use the beam propagation method with equivalent input noise for the simulation of narrow-band amplified spontaneous emission (ASE) and signal amplification in continuous-wave Cr²⁺:ZnSe non-waveguiding “bulk” amplifiers with non-saturating signal and ASE in different configurations with weak reabsorption. Both the incident pump at 1901 nm and the signal at 2410 nm were diffraction-limited gaussian beams. We implemented the equivalent input noise as random realizations of one photon per gridpoint, and showed that this leads to one noise photon per mode. Simulation results of between 100 and 6000 realizations were ensemble-averaged to determine the power spectral density of the ASE in a Monte Carlo approach. We validated the approach by comparing results for single-mode and multimode fiber amplifiers to those obtained with well-established fiber amplifier models. We also calculated the beam quality of the ASE, (:{M}_{ASE}^{2}), from its spatial distribution. We found that under some conditions, but not all, (:{{M}_{ASE}^{2}}^{2}) can serve as an estimate of an effective number of ASE modes and, together with the ASE PSD, predict the achievable signal gain. It is also possible to evaluate the PSD per unit solid angle due to spontaneous emission from the input noise seeding, and we found agreement down to the single-photon level.

We investigated a dual-wavelength twin-pulse laser with tunable intensity ratio and pulse interval, pumped by an 808 nm laser diode (LD), using Nd: GdVO₄ and Nd: YVO₄ as laser gain media, in conjunction with a Cr⁴⁺:YAG saturable absorber. A new theoretical model of a dual-wavelength twin-pulse laser based on intracavity gain-switched pumping has been established. The findings of the simulation show that it is possible to accomplish dual-wavelength twin-pulse laser output without gain competition. Moreover, the simulation underscores the capability to fine-tune the intensity ratio and the pulse interval between the two wavelengths. In the experiment, theoretical modeling served as a guide for key parameter settings. Ultimately, dual-wavelength twin-pulse laser outputs at 912 nm & 1064 nm were achieved, with a tunable intensity ratio ranging from 0.8 to 1.4 and an adjustable pulse interval from 18 to 6 ns. The experimental results aligned closely with the simulation outcomes.

A diode-pumped continuous-wave (CW) orthogonally polarized Sm: YAlO₃ (Sm: YAP) orange laser on ⁴G_5/2→ ⁶H_7/2 transition with output power ratio and wavelength tuning was demonstrated. By adjusting the tilt angle of the beam splitter (BS) and the rotation angle of the intracavity Lyot filters, multiple pairs of orthogonally polarized single-wavelength (OPSW) and dual-wavelength (OPDW) lasers were realized. The highest total output power with the OPSW orange laser at 604 nm reached 1.24 W at an absorbed pump power of 9.0 W at 405 nm, resulting in an optical-to-optical conversion efficiency of 13.8% with respect to the absorbed pump power. Besides, maximum balanced output power with the OPDW orange laser at 604 and 610 nm was 0.48 W, resulting in an optical-to-optical conversion efficiency of 10.7% with respect to the absorbed pump power. To the best of our knowledge, it is the first time to achieve Sm: YAP lasers.