Analysis And Diagnosis On Optical Film Laser Damage

Laser weapon is facing the challenges of high-power and high-energy,which require high performance of laser.However,the ability of laser damage resistance of optical components in a laser system takes the dominance in all the factors which potentially limit the development of laser.As a key component,optical film determines the ability of laser damage resistance of optical components.Therefore,the development of high-power and high-energy laser heavily relies on the improvement of optical film's laser damage resistance ability.Moreover,addressing the issues of how to improve the ability of laser damage resistance of optical films will accelerate the research process of high-power and high-energy laser.Although the interactions mechanism between laser and films are well known,experimental testing on various films is not sufficient.Laser-induced damage threshold(LIDT),regarded as an important indicator to measure the ability of the laser damage resistance of optical films,still needs further study on its testing accuracy.In this thesis,we focused on the recognition and evaluation of laser damage as well as the accurate measurement of LIDT of optical film.Series of work have been conducted as following.The research of optical film's plasma spectrum characteristics induced by pulsed laser:Based on the principles of atomic collision and stimulated radiation,the avalanche process and the degree of ionization of optical films that were irradiated and damaged by pulsed laser has been simulated with Maxwell and Saha equations under the condition of plasma's local thermodynamic equilibrium.The plasma sparking,which created by pulsed-laser irradiated optical film has been analyzed theoretically.This thesis focuses on the characteristics of plasma sparking spectrum.Utilizing peak position and width of atomic spectral line to obtain the temperature and electron density of optical films,reliable technical supporting for the research on interaction mechanism between the laser and the films can be realized.The research of plasma shockwave characteristics induced by the pulse laser irradiated optical film:By employed aerodynamics,unsteady gas dynamics and point explosion,the theoretical model of plasma shockwave from optical film was established after laser irradiation.The characteristics of plasma shockwave propagating in the air were simulated under the laws of conservation of mass,energy and momentum while experimental analyzing was taken with acoustic diagnosis method.The results illustrated that parameters of this plasma shockwave,such as velocity,pressure,temperature and etc.,decay exponentially when propagating in the air and has a direct relationship with absorbed laser energy.Therefore,the characteristics of laser-induced plasma shockwave are related to the laser damage of optical film.Notably,the theoretical analysis and the test results are consistent,which provide efficient testing experiment to further study the interaction mechanism between laser and film.Identification methods for laser damage of optical films:Two efficient exam modalities for detecting laser damage of optical film are presented:The first one based on the characteristics of laser induced plasma spectrum that solved misjudgments,which caused by atmospheric sparking and manual operation factor.By using the atomic spectral line of plasma spectrum as the criteria,the test accuracy of films' LIDT is improved.The second method,which based on the characteristics of laser induced plasma shockwave,has completed the damage detection by using acoustic diagnosis method.The latter not only provides high accuracy but also improve the optical film's LIDT testing efficiency.Experimental research on the key factors to laser-induced damage threshold of optical film:Based on the principles of heating effect and field effect work on the interaction between film and laser,experimental testing and detailed analyzing are presented to discover the influence of surface parameters of substrate and coating structure design on laser damage threshold of optical film.The modality added a bias electric field to the surface of film to study the laser-induced damage characteristics of Diamond-like Carbon Film(DLC)as well as the oxide film.The result shows that the laser-induced damage deducted significantly while the ability of laser damage resistance of the oxide dielectric films improved efficiently.