Study On Field Effects And Threshold Testing Of High Power Laser-Induced-Damage In Optical Components

The high power lasers for inertial confinement fusion such as National Ignition Facility (NIF) at Lawrence Livermore National Laboratory (LLNL) or the Laser Mega-Joule (LMJ) in France always work at extremely high power or energy. For some sense, the power level and the performance of the laser system are limited by the damage resistance of the components to intense laser illumination. Therefore, it is vital for the researchers and technicians working in high power laser area to get some knowledge about damage mechanisms or acquire the correct laser-induced-damage-threshold (LIDT) of the components. However, the laser-induced-damage in the optics is so complicated, for it is affects by lots of factors lying in physics or chemistry. It has been attracting the researchers' attention since the first high power laser system come into application. For these reason, this thesis focus on some laser-induced-damage mechanisms, LIDT testing experiment and laser conditioning, which is a feasible technology to improve the LIDT. The main results obtained can be summarized as follows:1. The requirement for laser-induced-damage research in ICF has been expatiated. The investigation history of damage mechanisms and testing has been summarized. Meanwhile, the complexity of laser-induced damage researching has also been analyzed.2. Thermal, stress and electric field changing of some optics during the interaction with the laser have been studied. A physical model have been set up to calculating the temperature distribution of the optical components irradiated by the periodic pulses by making full use of the periodic characteristics of the pulsed lasersystem. Some methods to get the thermal transfer stress in components have been introduced. Relations between laser-induced-damage and the electric field changing and the formation of the shock-wave in optics have been analyzed.3. The whole LIDT testing process has been introduced based on the LIDT testing station which was built up regulated by the ISO 11254 standard in Chengdu Fine Optical Engineering Research Center. Some methods to identify the damage have been presented. These methods could be beam-distortion detecting, scatting probing and so on. Theories on these methods have also been given. Furthermore, damage test experiments have been set up to study the damage characteristics and mechanism of the color-separating gratings (CSGs) and silica irradiated by the 1064 nm and 355 nm laser respectively.4. The origins of the uncertainty of LIDT testing result have been completely deduced. An operable model to calculate the relative combined standard uncertainty of LIDT has been set up. As an example, it has been successfully applied to analysis the uncertainty of the LIDT of the 1064 nm HR thin-film sample.5. The laser conditioning method has been studied, which can extremely improve the LIDT of the optics, especially coatings. Methods of laser conditioning have been investigated, such as R-on-1, N-on-1, single-step off-line and 2-step laser conditioning process. Modes like modular benign ejections have been applied to explain the LIDT improvement by the laser conditioning. Finally, an experiment with 1064 nm Nd:YAG laser conditioning on HfO2/SiO2 coating samples has been set up to study the improvement effect of damage threshold.