| 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. |
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