Temperature Effect Of Optical Components Under Ultrashort Pulse Laser Irradiation

The controlled nuclear fusion by inertial confinement fusion(ICF)is expected to become a new alternative of fossil fuels energy in the future.The load capacity of high power solid-state laser devices for ICF research is one of the main technical indicators to measure its comprehensive performance,and the laser damage resistance of optics has become an important factor of the load capacity of the entire device.By the research on the physical mechanism of laser induced damage of the optics,it is found that the decrease of the temperature can effectively suppress the thermal effect of the optics under the irradiation of long pulse laser and reduce the increase of conduction band electron density resulted from avalanche ionization during short pulse irradiation,so that the laser induced damage threshold of the optics can be increased.In this paper,the laser induced damage thresholds of fused silica and K9 glass at different temperatures(296K~86K)was measured and the relationship between temperature and laser damage threshold was explored.Then we use the impurity-containing thermal explosion model in the nanosecond region and the temperature generation rate equation in the femtosecond region to simulate the experimental results and analyze the physical mechanism of the temperature curve.The main research contents include:1.Fused silica and K9 glass samples were prepared by different pretreating methods and irradiated under different ambient temperature.The 355 nm nanosecond laser induced damage thresholds were measured by visible light reflection method and N-on-1 method.The experimental results show that the damage thresholds increase first and then decrease with the decreasing of temperature,and there is a temperature independent of the sample pretreatments,at which the damage thresholds reaches the maximum value.The maximum increase of acid-etched fused silica at that temperature was 21.12% more than that at ambient temperature,and the value for acid-etched K9 glass was 24.36%.And the maximum increase of fused silica after acid etching was 66.06% more than that at ambient temperature without acid etching,and the value for K9 glass after acid etching was 31.08%.Then we use the impurity-containing thermal explosion model to simulate the experimental results and the results showed that the temperature curve of the damage threshold was mainly dependent on the critical damage temperature and the nonlinear absorption coefficient of the materials.The experimental results are in good agreement with the results of numerical simulation in all aspects.The results show that the combination of temperature and pretreatment can greatly improve the damage threshold of the material,and has a good potential application value in engineering.2.The femtosecond laser induced damage thresholds of fused silica and K9 glass under single pulse and multi-pulse irradiation were measured by using the damage area extrapolation method.Under the irradiation of 800 nm 260fs laser,the single pulse laser induced damage threshold did not obviously change with the decreasing of temperature,and was not consistent with the results of numerical simulation based on quantum methods or classical methods(damage threshold increases with the temperature increase).As the number of pulses increasing,the multi pulse laser damage threshold decreased rapidly and then approached stable.The results showed that under the irradiation of 150 fs pulse,avalanche ionization is not dominant in the electron density increasing.Under the irradiation of 800 nm 530fs laser,the damage threshold of both single pulse and multi-pulse appeared to increase and then decrease with the decreasing of temperature.But because the effective data obtained is not sufficient,further experimental verification was needed.