高重频CO2激光损伤HgCdTe晶体的机理研究

	高重频CO2激光损伤HgCdTe晶体的机理研究
	汤伟
学位类型	博士
导师	郭劲
	2014-07
学位授予单位	中国科学院大学
学位专业	光学工程
摘要	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材料的结构特性、热学特性、光学特性和缺陷特性等基本特性，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) 基于热传导微分方程，推导了强激光辐照下HgCdTe晶体的单脉冲熔化阈值、熔化时间和烧蚀深度的解析表达式，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现象。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。
其他摘要	Damage mechanism of HgCdTe crystal irradiated by high repetition frequency CO2 laser is systematically studied in this paper. Firstly, physics properties of HgCdTe materials are introduced and thermal and optical parameters are obtained. Secondly, temperature rise and damage characteristics of HgCdTe crystal irradiated by high repetition frequency CO2 laser are obtained by theoretical analysis and experiments, a general rule on the temperature rise and damage characteristics is given. Finally, damage mechanism of HgCdTe crystal is analyzed by damage morphology and the composition changes of the crystal and calculation of the stress. A few research results and innovative and innovative conclusions are obtained in our research. In summary, main research results and conclusions in this thesis are as follows:(1)The analytical solutions of melting threshold, melting time and ablation depth on single pulsed laser irradiating HgCdTe crystal are given basing on heat conduction equation. Melting threshold, melting time and ablation depth of Hg0.826Cd0.174Te crystal damaged by single pulsed CO2 laser is calculated. Theoretical results show that: melting threshold of Hg0.826Cd0.174Te crystal damaged by single pulsed CO2 laser is 31.8J/cm2.(2)Damage characteristics for the onset of surface melting was investigated theoretically and experimentally on Hg0.826Cd0.174Te crystal irradiated by high repetition frequency CO2 laser. The impact of repetition frequency and irradiation time on damage threshold was analyzed. The results show that damage threshold doesn’t depend on laser repetition frequency and gradually reduces with the increase of irradiation time. While once the irradiation time is more than 10s，damage threshold is a constant value, and the value is 0.95kW/cm2. In addition, damage threshold calculated by theoretical model is in good agreement with the experimental data.(3)Mechanical characteristics of Hg0.826Cd0.174Te crystal irradiated by single pulsed laser and multi-pulsed laser are calculated. Theoretical results show that stress on the crystal surface irradiated by single pulse laser is mainly thremal stress and evaporation pressure before melting and thremal stress after melting, while stress on the crystal surface irradiated by multi-pulsed laser is mainly thremal stress because of low peak power density. In addition, SEM results show that the main way of Hg0.826Cd0.174Te crystal damaged by multi-pulsed laser is melting damage, melting and solidification phenomenon were very obvious on the crystal surface, and the obvious crack which was caused by thermal stress was not found.(4)Chemical component measurement results show that chemical composition changes of the crystal are obvious, and a lot of O element is found in the laser ablation zone. With the increase of laser irradiation power, the content of Hg element decrease rapidly, the content of Cd、Te and O element raise by degrees. The main cause of Hg loss 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 is irradiated by pulsed CO2 laser.
语种	中文
文献类型	学位论文
条目标识符	http://ir.ciomp.ac.cn/handle/181722/41471
专题	中科院长春光机所知识产出
推荐引用方式 GB/T 7714	汤伟. 高重频CO2激光损伤HgCdTe晶体的机理研究[D]. 中国科学院大学,2014.

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