Sealing design is an effective way to prevent pollution of high power laser. The thermal stress and installation distortion of sealed optical window seriously affect the quality of laser beam. Based on the design scheme of glueless welding seal, this paper fully considering the material, absorption rate and welding layer interaction of the optical window and the base, combined with the finite element simulation method, the distortion of the sapphire and fused silica optical window surface caused by temperature drift and the installation stress was calculated. through the optimization and simulation of the V-shaped flexible release form of the installation stress, the physical model of the optimal design is obtained. Then, the temperature field, deformation and refractive index distribution of the optical window assembly is analyzed during the TEM00 mode Gaussian beam lasing process and the effect of optical window surface distortion, defocusing amount and beam quality degradation with lasting time is calculated. At last, the influence of the change of the internal and external pressure difference is calculated. The results show that the leakage rate after welding is better than 10-12Pa·m3/s, RMS of the mounting surface accuracy is 0.013 λ. The laser power is 10kw and the light lasting time is 120s, the laser beam quality degradation rate β < 1.1, the relax meets the system requirements. The research results provide an important reference for the design, simulation analysis, laser transmission beam quality control and correction of high-power laser anti-pollution and sealed light window components.
Stimulated Raman scattering (SRS) must be suppressed owing to its adverse effect on high-power fiber lasers. We propose a bending-sensitive multi-ring fiber composed of three parts: a core, multiple high-refractive-index rings, and a cladding. Appropriate bending of the fiber produces a high loss of the first-order Raman Stokes wavelength at 1114 nm and low loss of the signal wavelength at 1064 nm, thus enabling the signal light to be confined to the core while maintaining single-mode transmission. This principle relies on the resonant coupling between the core and ring modes. Numerical analysis indicated that the loss ratio of the fundamental mode could reach 2650.041 by optimizing the structural parameters. Moreover, when the three-ring fiber was subjected to a bending radius of 6 cm, a bend-induced loss of the Raman wavelength reached 11.315 dB/m, which effectively suppressed the first Stokes SRS generation.
An Electro-optical Q-switched Nd:YAG slab laser with a crossed misalignment Porro prism resonator for space applications has been theoretically and experimentally investigated. The phase shift induced by the combination of different wave plates and Porro prism azimuth angles have been studied for creating high loss condition prior to Q-switching. The relationship of the effective output coupling reflectivity and the employed Q-switch driving voltage is explored by using Jones matrix optics. In the experiment, the maximum output pulse energy of 93 mJ with 14-ns pulse duration is obtained at the repetition rate of 20 Hz and the optical-to-optical conversion efficiency is 16.8%. The beam quality factors are M 2 x = 2.5 and M 2y = 2.2, respectively.
A novel high average power double slab laser with hybrid resonator is presented. By analyzing and simulating thermal distribution of the face-pumped slab medium, it is found that the thermal distortion of wave front caused by the non-uniform temperature distribution of the laser gain media can be self-corrected in this structure. According to the analysis of the slab thermal distribution, a hybrid resonator is presented. Using a plane-wave or k-space expansion together with the fast Fourier transform, mode patterns, power outputs from the laser are calculated. Far-field characteristic and beam quality of these modes are discussed. And besides, by comparing the properties of off-axis hybrid resonator with the on-axis hybrid resonator's, the off-axis hybrid resonator can produce better quality beam.
A novel scheme of the face-pumped double-slab Nd:YAG slab medium cooled by liquid with different temperatures on both sides is proposed. In this structure the thermal distortion of wavefront caused by the non-uniform temperature distribution in the laser gain media can be self-compensated. According to the running mode, the model of the slab medium’s temperature distribution and stress are presented. The analytic solutions for the model are derived. Furthermore, the numerical simulations with pulse pumping energy of 10J and repetition frequencies of 500Hz and 1000Hz are calculated for Nd:YAG laser medium. The simulation results show that the temperature gradient remains the approximative linearity, and the heat stress is in the range of stress extremes. Then the absorption coefficient is also discussed. The result indicates that the doped concentration cannot be too larger for the high repetition frequency laser. It has been prove that high repetition frequency, high average output power of the order of kW of Nd:YAG slab laser with high laser beam quality can be achieved in this structure.
An optimization model of laser diode (LD) pumped, passively Q-switched, intracavity frequency doubled solid state laser was proposed. The output energy is maximized by optimizing the length of doubling crystal and the initial transmission of saturable absorber. It provides a design criteria of a compact laser source for micro pulse lidar (MPL). The pulse repetition frequency (PRF) is controlled to meet the requirement of MPL. Numerical simulation examples are present to shows the relationship between the output energy and optimized parameters.
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