Numerical analysis of the thermal and mechanical effects of laser windows of a high-power all-solid-state 2-μm laser system

Abstract

Abstract. The output window of a high-power laser system is vulnerable to damage, and this is the main limiting factor on the power scaling and structure integrity of the laser system. In endeavoring to obtain higher output powers from the laser system, the impact of the thermal and mechanical effects and the damage mechanism of the output window must be considered. In order to study these issues, a thermal model of the laser window is established based on the heat transfer and thermoelastic theories, and the expressions for the transient thermal and mechanical stress distributions of the output window are deduced in terms of the integral-transform method. Taking the infrared quartz window material as an example, the temperature and mechanical field distributions of a high-power all-solid-state 2-μm laser system window are simulated, and the laser-induced damage mechanism is deeply analyzed. The calculation results show that the laser window-induced damage is mainly caused by melting damage when the temperature exceeds the melting point of the material. The presented theoretical analysis and numerical simulation results are significant for the design and optimization of high-power laser windows. © The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI. Keywords: laser window; temperature field; mechanical stress field; laser-induced damage mechanism.Paper 131586 received Oct. 17, 2013; revised manuscript received Jan. 2, 2014; accepted for publication Jan. 6, 2014; published online Feb. 4, 2014. IntroductionHigh-power all-solid-state 2-μm laser systems have played an increasingly important role in the technological landscape during the past few years. Applications have ranged from an abundance of medical uses, such as laser surgery and therapy, to more technical applications, such as laser ranging and remote sensing. [1][2][3][4] It is important to develop a laser system with high efficiency, long lifetime, and high stability; however, the laser output window may compromise the system's performance because of the thermal and mechanical effects caused by the window absorption in the process of high-power laser-beam outputting, which not only limits the service life, but also affects the power scaling of the system. 5 The thermal-mechanical effects and the damage mechanism of the laser output window have to be studied for further improving the power levels of the system before the onset of window damage. 6 These issues have received a great deal of attention, and various models have been proposed including the heating conduction model, the multiphoton ionization model, and cumulative ionization breakdown. Studies have shown 7,8 that the multiphoton ionization model and cumulative ionization breakdown dominate only in the case of high-power pulsed output, such situations have difficulties in quantitative analysis, and the heating conduction model i...