Research On Plasma Shock Wave Characteristics Of Thin Film Damage

With the development of science and technology,the optical system is used more and more widely,and the optical film is the core part of the optical system,that will be paid more attention.The main function of the thin film is to control the quality of beam transmission and protect the system from damage.However,under the action of high power laser,the damage of the thin film in the optical system is inevitable.Once the damage occurs,it will affect the function of the whole system.The most important parameters to measure the stability of the film is the laser damage threshold.The optical thin film was always damaged under laser irradiating by the plasma shock wave.Therefore,it is very important to study the characteristics of plasma shock wave.Based on a lot of theoretical research,appropriate plasma shock wave acquisition and processing equipment were chosen to set up the experimental platform of collecting the plasma shock wave.This paper studied on the propagation and attenuation of plasma shock wave in the air,and according to the experiment the relationship between the frequency characteristics,as well as strength,of plasma shock wave and laser energy were analyzed.Finally,the method of measuring the damage threshold of the film is obtained depend on the strength of the plasma shock wave.Put the microphone in different positions of the shock wave field,collecting the signal under the same condition many times to obtain the characteristics of shock wave in different positions.Change the distance between the microphone and the irradiation to get the time from the start of laser pulse to signal was collected,Then the number of Mach spread in a fixed distance can be gotten.Change the laser energy and collect the signal in the same position to research the frequency and strength of the shock wave,after that the relationship between the two and laser energy can be approached.According to the relationship between the laser energy and the strength of plasma shock wave,as well as the damage of the film,we can get the damage identification method of the thin film by the plasma shock wave.Experimental results show that the plasma shock wave surface in the air like sphericity and the number of Mach will decay rapidly sound velocity when it spreads some centimeters.The frequency of plasma shock wave will decrease with the laser energy increasing,but the strength is just opposite.According to the laser damage threshold and the relationship between the strength of the wave and laser energy,the damage identification basis of the thin film by the plasma shock wave.The experimental results show that the method is of high accuracy and fast identification that can be used in many trades.