Thermal And Mechanical Damage Effects Of Optical Lenses Irradiated By Femtosecond Pulsed Laser

Due to the large power density and good collimation of pulsed laser,many countries are eager to develop high-power,high frequency and short pulse lasers with small volume,low power consumption,long coverage and strong capacity of resisting disturbance.It is more conducive for high-power lasers to blind or even destroy enemy satellites as anti-satellite killer in the special space environments.The precise optical lens is their weak links of an reconnaissance satellite.During the interaction between the laser and materials,the energy of the laser pulse will undergo a series of complex transformation processes into other forms of energy,in which the thermal and mechanical energy have the strongest damage effect to the material,therefore the thermal and dynamic effects of the laser to materials have always been the key points in the fields of laser damage and laser processing.Therefore,in order to promote the development of high-energy laser weapon platform and the progress of laser damage protection technology of optical system,the thermal and mechanical damage experiment of optical lens irradiated by femtosecond laser was carried out.The main results are as follows:a)A measuring system for the surface temperature field of laser irradiated materials was established.Temperature variation near the irradiation point of lens surface is obtained under different optical lens materials and pulse repetition frequency.The variation law of laser thermal effect was explained combining with mechanical effect.The results show that there is a positive linear correlation between the repetition frequency of the output laser pulse and the maximum temperature in the lens surface temperature field,and the higher the frequency is,the greater the temperature gradient is.b)The transient stress and dynamic stress-strain measurement system under pulse irradiation was constructed.The whole process from the beginning action of laser pulse to the attenuation of stress wave in target plate was measured.The GPa-level stress attenuates to KPa-level Lamb wave at the end of pulse irradiation.At the same time,the curves of stress or strain changing with time and pulse frequency on the surface of optical lens or in its matrix are obtained.To a certain extent,the complex coupling mechanics effect is preliminarily decoupled.c)High-speed photography and microscopy were used to observe the damage of optical lenses at quasi-micro and micro scale.The whole physical process of the interaction between laser pulse and transparent optical glass was clarified,and the micro-damage morphology of laser irradiation point was obtained.Laser plasma oscillation frequency is 1000Hz.When the heat and charge accumulate to a certain extent,discharge and detonation will occur.Ablation and perforation at the focal point are accompanied by a large number of microcracks.d)The antireflective coating on the surface of optical lens will increase the distortion of heat-affected zone and temperature field,decrease the temperature gradient,interfere with the propagation of Lamb wave in the substrate,cause the plasma discharge ahead of time,delay the detonation phenomenon,and reduce the penetration depth.It is concluded that the coating has a good protective effect on the optical lens substrate.