The thermal focal length of the side-pumped module was first measured at different pump currents, revealing a relationship between thermal focal length and pump current. Then, a linear resonant cavity was designed and optimized. A 1064 nm pulsed laser was generated by using LD side-pumped Nd:YAG laser and acousto-optic(AO) Q-switching technology. BBO and LBO crystals were utilized for second-harmonic generation (SHG) and sum-frequency generation (SFG), respectively. At a repetition rate of 8 kHz, the maximum average power of the 355 nm ultraviolet (UV) output reached 2.13 W, with a pulse width of 32.7 ns. The optical-to-optical conversion efficiency from 1064 nm to 355 nm was 24.3%. At last an analysis was conducted on the impact of the 1064nm to 532 nm photon number ratio's impact on SFG, and the optimal power ratio is close to 1:2 for achieving high conversion efficiency of 355 nm laser output.
Alexandrite crystal is a broadband tunable gain medium with good performance in near infrared band. At room temperature, the wavelength tuning range of the alexandrite laser is about 700~818nm, UV or deep-UV (DUV) lasers can be obtained by single or multiple optical nonlinear frequency conversions. The laser oscillations can be generated when alexandrite crystals absorb pumping light energy, and a considerable part of pumping energy will be converted into thermal energy of crystals which will lead to a thermal effect. It will affect the output laser efficiency, the stability of resonator and the quality of output laser beam. In this paper, by establishing the thermal conduction model of the crystal, the stable temperature field distribution, deformation field distribution, and thermal stress field distribution in the crystal can be obtained by solving the corresponding equations. Then the thermal effects caused by these three fields are analyzed respectively, and the corresponding focal lengths of thermal are calculated which shows an inverse relationship between the focal length of the thermal and the absorption pumping power when other conditions remain unchanged. The stable parameter range of the laser cavity can be obtained according to the stable conditions of the resonator, and it will play a guiding role in solving the thermal effect of the crystal and improving the performance of the laser.
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