【作者】 张震；

【导师】 于欣；

【作者基本信息】 哈尔滨工业大学 ， 物理电子学， 2008， 硕士

【摘要】 固体激光器由于温度分布不均引起的热透镜效应、热致衍射损耗和热炸裂等热效应,已成为制约其向高功率、高光束质量、低功耗、小型化长寿命方向发展的瓶颈,因此,必须发展有效的冷却技术才能解决高热负荷激光器的冷却问题,而微通道热沉冷却由于体积小、换热系数高等优点,是一种很好的选择。本文概述了固体激光器的冷却技术,特别是近年来出现的新型独特的冷却技术。利用热分析的有限元法,在详细分析准三能级激光器热效应的基础上,结合对LD(Laser Diode)输出泵浦光的实验测量,考虑多模输出、近高斯分布等多种因素,较为准确地建立了块状激光晶体热传导的有限元模型,模拟了晶体在不同换热边界条件下的温度场、温度梯度场和热应力场分布,提出了改善激光晶体散热性能的有效措施。阐明了微通道热沉的设计原理,完成了微通道热沉的设计、加工和表面处理。基于微通道热沉进出口水温和晶体边界环境温度的理论分析和实验测量,指出了人们对晶体边界环境温度即为冷却剂温度的假定是不够准确的,通过微通道热沉与普通热沉散热的对比实验研究,验证了微通道热沉优良的散热性能。测量了微通道的流阻变化,为优化设计微通道结构和合理选择冷却水流量提供了依据。有限元分析结果表明,提高对流换热系数或降低晶体边界环境温度,可显著降低晶体整体温度,但温度梯度变化较小,且换热系数达到最大值后,继续强化外部换热几乎不改变晶体的温度和热应力场分布。本文设计、加工出了通道宽度为0.2mm,肋片厚度为0.8mm的微通道热沉。针对紫铜微通道在加工过程产生的污垢,开发了表面处理工艺,完成了组装,并成功应用于固体激光器的冷却上。利用微通道热沉散热,在LD端泵Nd:YVO4输出914nm激光实验中,相同实验条件下,与普通热沉相比,输出斜坡效率提高了14%,输出功率为6W时,光束质量因子M2由3.35改善为2.00,最高输出功率增加了1.5W,达到8.9W,据我们所知,这是目前有报道的最高水平。结果表明,微通道冷却技术可缓解晶体的热效应,有效提高激光器的激光输出功率和改善光束质量,且在高泵浦功率下,将体现出更明显的优势。更多还原

【Abstract】 Thermal effect including thermal lens, diffraction loss, thermal fracture induced by inhomogeneous heating of the laser material in the solid state lasers has restricted the development of lasers to high output power, high beam quality, compact configuration, and long life. Therefore, effective cooling technologies will developed in order to solve the high thermal load in the lasers, and micro-channel cooling provides a good choice because of its compact geometry, high heat transfer coefficient.This paper summarizes the cooling technologies in solid state lasers, especially for novel and unique technologies. Considering the profile and the multi-mode of the pumped beam measured in the experiment, the finite-element modal of the heat conductive function in the laser crystal is developed on the basis of analysis of thermal effect in quasi-three level lasers to simulate the temperature field, the temperature grads field and thermal stress distribution. The schemes for heat removed in the laser crystal are advised. The principle of devising micro-channel geometry is illuminated. The design, machining, and the surface disposal of it is finished. The assumption of the boundary temperature on the crystal in some papers is found to be not quite correct by the measurement experiment. Micro-channel’s ability of heat removal is proved by the contrasting experiment between micro-channel heat sink and common heat sink.The finite-element analysis of thermal effect in the laser crystal indicated that the whole temperature dropped but the temperature grads decreased little by increasing the convective coefficient and decreasing the boundary temperature of the crystal. Additionally, the maximum convective coefficient is found and excess not contributed much to changes of the temperature field and thermal stress. The maximum stress emerged nearby the center pumped side and fraction occurs at this point when pump power increases.This paper finished the designing and machining of the copper micro-channel with channel width 0.2 mm and fin width 0.8 mm. The technique of surface disposal is explored and the installment into solid state lasers is accomplished.In LD end-pumped 914nm Nd:YVO4 quasi-three-level lasers, the slope efficiency of output laser rises 14% , M2 alters to 2.00 from 3.35, and maximum output power up to 8.9W, rises 1.5W, with the micro-channel heat sink for heat removed, comparing to the common heat sink. The result indicates that the output power of the laser can be enhanced and beam quality can also be improved because the thermal effect is alleviated by the schemes of micro-channel cooling..更多还原