Study On The Influence Of Laser Parameters On The Laser Damage Threshold Of Thin Films

With the high-power and high-energy laser systems are increasingly used in scientific research and industry,optical film components have become a key link in high-power and high-energy laser systems.Once the optical film damaged,it will affect the performance of the entire system.The most important parameter for judging the stability of an optical film is the ability of the film to resist laser damage.Usually,the laser damage resistance of the film is represented by the laser damage threshold.In order to better judge the laser damage resistance of the optical film,it is necessary to accurately measure the film damage threshold.However,laser parameters are the most direct influencing factors for obtaining high-accuracy film damage thresholds.Therefore,it is very meaningful to study the influence of laser parameters on the damage threshold of thin films.Based on theoretical analysis and experimental tests,the influence of laser parameters on the damage threshold of the film is studied.Through the establishment of laser parameters with film damage threshold numerical model and computer simulation,the effects of laser output energy,focused spot size and M~2 factor on the damage threshold of the film are theoretically analyzed.Meanwhile,based on the research of common laser beam shape parameters measurement methods,the measurement method of Shack-Hartman wave-front detection is proposed,which the measurement principle is elaborated.A laser beam shape parameters measurement system with Shaker-Hartman as the main detection device is designed and built to measure the actual light intensity distribution of the laser beam,and the focused spot size andM~2 factor is calculated according to the second moment definition of the light intensity distribution,and compared the measured value with nominal value.According to the principle of repeatability and equal precision tests,the laser output parameters and the damage threshold of the film samples are measured multiple times,and the effects of laser energy,focused spot size andM~2 factor output stability on the film damage threshold are analyzed.Last,the uncertainty of the film damage threshold is calculated by statisticalprinciple.The experimental results show that the stability of the laser output parameters is poor,the maximum energy relative error is 9.99%,the maximum relative error of the focused spot size is 7.81%,and the M~2 factor average measurement is 7.7,which is far from the ideal value of the fundamental mode Gaussian beam.The laser output energy error and the focused spot size error are proportional to the film damage threshold error.TheM~2 factor is inversely related to the film damage threshold.The relative uncertainty of the damage threshold synthesis caused by the energy error and the focused spot size error is18.72%.It is verified by experiments that the stability of the laser energy,the focused spot size and the the beam quality have an impact on the accurate measurement of the damage threshold of the film.Therefore,studying the influence of laser parameters on the film damage threshold provides a direction for obtaining accurate filmdamage threshold test results.