Study On The Thermal Effect In Solid-State Tube Laser

Solid-state tube laser (SSTL) is one of available laser with high power output, for its high slop efficiency and electro-optical efficiency compared to the solid-state rod laser. As the laser tube can be cooled both on the inner- and outer- surfaces of the tube, the thermal effect in SSTL is smaller than that in a rod laser with the same geometry size. Although SSTL could allow a higher thermal load than flash lamp pumped rod laser, thermal effects always restrict the SSTL developing to high power output, especially under a farther high power pumping. Therefore, studies on the thermal effects in SSTL are of momentous significance. In the dissertation, the thermal effects in CW SSTL or repeated pulsed SSTL of low frequency and SSTL of low frequency have been analyzed theoretically.The main results obtained in the dissertation can be summarized as follows:Firstly, the thermal effects in the inside-pumped SSTL have been analyzed simply based on the 1/r heat deposit model. The stress induced birefringence and thermal depolarization have been simulated numerically under different tube thickness and different pumping power. The results show that the stress induced birefringence increases with the tube thickness for a fixed heat deposit intensity, and grows with the pumping power for a fixed geometry size, and so does the ring number of the thermal depolarization pattern.Secondly, for the CW or repeated pulsed SSTL of high frequency, theconditions of gas cooling of the two end surfaces and water cooling of the inside and outside of the tube have been considered, which was not taken into account before. Based on the quadratic absorbing heat deposit model, the temperature rise in the tube has been calculated under different thickness, pumping power, reflectivity of the reflector, and absorbing efficiency of the laser medium. The results show that the temperature rise of the inside-pumped SSTL is different from that of the rod laser, and at the steady state, the temperature rise distribution on the cross-section of tube is annular. The temperature rise is larger inside the tube as compared to that at the inner- and outer- surfaces of the tube, and the temperature rise of the inner surface is bigger than that of the outer surface.Thirdly, the dynamic 3-dimensional temperature rise distribution has been studied for a tube YAG laser inside-pumped by periodically repeated optical pulses with a low frequency. The end cooling and inner- and outer surfaces cooling have been taken into account. The 3-dimensional dynamic temperature rise at different time has been calculated based on the 1/r heat deposit model. The results show that, at the beginning, the transient temperature rise with the number of pump pulses in the tube increases following a saw-toothed like curve, and finally after a number pulses, repeats itself at a period equal to that of the pump pulses. And the position of the maximum transient temperature rise shifts from the inner surface to the inside of the tube, and finally occurs at a fixed point.The results obtained in this paper can be used to optimize the design of SSTL oscillators or amplifiers.