【作者】 汤伟；

【导师】 郭劲；

【作者基本信息】 中国科学院研究生院(长春光学精密机械与物理研究所) ， 光学工程， 2014， 博士

【摘要】 激光辐照效应是目前国内外激光技术领域研究热点之一，HgCdTe晶体作为一种性能优异的红外光学材料，被广泛应用于红外探测器的制备。由于HgCdTe探测器在红外波段具有高探测率、响应波段可调以及工作温度范围较宽等优点，目前在国防军事、工业等领域得到了广泛的应用。高重频CO2激光长时间辐照下，HgCdTe材料或器件表面会发生多脉冲损伤。因此，研究HgCdTe材料或器件的多脉冲损伤机理，掌握高重频CO2激光作用下HgCdTe晶体的损伤规律是非常有意义的。本文系统地研究了脉冲调Q CO2激光辐照下HgCdTe晶体的多脉冲破坏机理，首先介绍了HgCdTe材料的结构、热学、光学和缺陷等基本特性，了解了HgCdTe材料的光学和热学参数；然后通过理论与实验相结合的方法，得到了高重频CO2激光作用下HgCdTe晶体的温升特性和损伤特性，给出了HgCdTe晶体温升、熔化阈值、熔化深度与激光重频、辐照时间的一般性规律；最后通过对损伤形貌和组分变化的测量以及应力的计算，得到了多脉冲CO2激光辐照下HgCdTe晶体的损伤机理。在研究过程中，我们取得了一些研究成果和创新性的结果结论。概括起来，本文的主要研究结果和结论如下：1.建立了强激光辐照HgCdTe晶体的一维热传导解析模型，从理论上计算得到了脉冲调Q CO2激光辐照下Hg0.826Cd0.174Te晶体的单脉冲熔化阈值、熔化时间和烧蚀深度；理论结果表明：对于ns激光而言，Hg0.826Cd0.174Te晶体的单脉冲熔化阈值约为31.8J/cm2。2.从理论和实验上研究了高重频CO2激光辐照Hg0.826Cd0.174Te晶体热损伤特性，分析了Hg0.826Cd0.174Te晶体温升特性和熔化阈值与激光重频和辐照时间的关系，研究结果表明：高重频CO2激光辐照下，Hg0.826Cd0.174Te晶体的温升过程和熔化阈值与激光重频的大小无关，晶体的熔化阈值应由平均功率密度来表征，且受辐照时间的影响，随着辐照时间的增加，晶体熔化阈值逐渐减小，然而当熔化阈值减小到某一值时，受热平衡的影响此时晶体的熔化阈值不再改变，其大小为0.95kW/cm2，理论模型与实验结果基本一致，进而证明了实验结论的正确性。3.分析了单脉冲和多脉冲下Hg0.826Cd0.174Te晶体表面的力学效应，理论结果表明：对于单脉冲激光，熔化前晶体表面主要受热应力和蒸发波压力作用，而熔化后晶体表面主要受蒸发波压力作用；而多脉冲下，由于激光峰值功率低，晶体表面的应力主要受激光热应力影响。通过对晶体损伤形貌分析可知：高重频CO2激光辐照下HgCdTe晶体的损伤应为热熔损伤，扫描电镜下晶体表面熔化现象明显且未发现有裂纹产生，应力分析结果支持实验结果。4.材料组分测量结果显示：损伤前后晶体组分变化明显，辐照区内出现了大量的O元素，随着辐照功率的增加，Hg元素的含量迅速减小，而Cd、Te和O元素的含量逐渐增加；分析认为Hg损失的主要原因是HgCdTe晶体中化学键Hg-Te键在激光热作用的影响下不稳定，易发生断裂，从而导致Hg蒸发，含量减少；而出现O元素主要是由于高温环境下晶体与空气中O2接触发生的氧化反应所致。更多还原

【Abstract】 In recent years, laser irradiation effect is one of the most important researchfields. HgCdTe crystal is an infrared optical material of high performance and iswidely used to manufacture infrared detectors. Because of its high detectivity、adjustable response spectrum and wide operating temperature range in the infraredwavelengths, HgCdTe devices are widely used in the national defense, industry andother fields. In the prolonged irradiation of high repetition frequency CO2laser,HgCdTe materials or devices are damaged by multi-pulsed CO2laser. While damagemechanism of the materials or devices irradiated by multi-pulsed laser is differentfrom single pulsed laser. Therefore, it is very significant to obtain damage mechanismand characteristic of HgCdTe materials or devices in multi-pulsed laser irradiation.Damage mechanism of HgCdTe crystal irradiated by high repetition frequencyCO2laser is systematically studied in this thesis. Firstly, physics properties ofHgCdTe materials are introduced and thermal and optical parameters are obtained.Secondly, temperature rise and damage characteristics of HgCdTe crystal irradiated byhigh repetition frequency CO2laser are obtained by theoretical analysis andexperiments, a general rule on the temperature rise and damage characteristics isgiven. Finally, damage mechanism of HgCdTe crystal is analyzed by damagemorphology and the composition changes of the crystal and calculation of the stress.A few research results and innovative conclusions are obtained in our research.In summary, main research results and conclusions in this thesis are as follows:1. The unidimensional analytical model of HgCdTe crystal irradiated by highpower laser is set up. Melting threshold, melting time and ablation depth of Hg0.826Cd0.174Te crystal damaged by single pulsed CO2laser is calculated in the theroy.Theoretical results show that: melting threshold of Hg0.826Cd0.174Te crystal damagedby single pulsed CO2laser is31.8J/cm2.2. Damage characteristics for the onset of surface melting was investigatedtheoretically and experimentally on Hg0.826Cd0.174Te crystal irradiated by highrepetition frequency CO2laser. The impact of repetition frequency and irradiationtime on damage threshold was analyzed. The results show that melting threshold isindependent of laser repetition frequency and gradually reduces with the increase ofirradiation time. While once melting threshold is less than a constant value，the valueof which is0.95kW/cm2, melting threshold of the crystal never change. In addition,damage threshold calculated by theoretical model is in good agreement with theexperimental datas.3. Mechanical characteristics of Hg0.826Cd0.174Te crystal irradiated by singlepulsed laser and multi-pulsed laser are calculated. Theoretical results show that stresson the crystal surfaceirradiated by single pulse laser is mainly thremal stress andevaporation pressure before melting and thremal stress after melting, while stress onthe crystal surfaceirradiated by multi-pulsed laser is mainly thremal stress because oflow peak power density. In addition, SEM results show that the main way ofHg0.826Cd0.174Te crystal damaged by multi-pulsed laser is melting damage, meltingand solidification phenomenon are very obvious on the crystal surface, and theobvious crack which is caused by thermal stress was not found. Theoretical results arein good agreement with the experimental results4. Chemical component measurement results show that chemical compositionchanges of the crystal are obvious, and a lot of O element is found in the laser ablationzone. With the increase of laser irradiation power, the content of Hg element decreaserapidly, the content of Cd、Te and O element raise by degrees, and chemicalcomposition changes of the crystal are more and more obvious. The main cause of Hgloss at A and B point is that the Hg-Te key in the crystal is not stable and easily breaks.O element on the crystal surface mainly is from oxidation when the crystal isirradiated by pulsed CO2laser.更多还原