The Reasearch On Measurement Of Laser Damage Threshold Of Optical Thin Films By Space-time Resolution

With the continuous development of laser technology,the laser damage of optical components has become a major factor restricting its development.Therefore,laser damage threshold measurement technology has become an important research content.Laser damage threshold test methods and standards have undergone a long period of development.Since previous laboratories did not form a uniform test standard,by the 1990 s,the ISO 11254 optical element laser damage test standard was established under the ISO International Standard System.In 2011,the international laser damage threshold test standard ISO21254 was established and improved.The international standard laser damage threshold test method has become the most objective assessment method for the optical component's resistance to laser damage.However,there are still problems worthy of studying in practical test applications.In the international standard laser damage threshold test,the premise of the light spot equivalent area is that the laser damage is caused by the peak light intensity destruction,and the non-uniform energy density in the test laser spot is equivalent to the energy density corresponding to the peak light intensity.Therefore,this means that different defects within the test laser spot will not be resolved.This article did the following work on such issues:In this paper,the gaussian laser beam is spatially distributed.By subdividing the laser intensity distribution,and the spatial correlation between subdivided laser intensity and defect destruction is established,and the difference of laser damage threshold induced by different intensity positions of the defect in the laser beam is distinguished.The laser damage threshold induced by different defects in the optical film is measured objectively.The electric field distribution of the optical film is modulated by the film structure,and the electric field indensity of the defects are different at different depths in the film growth direction.The normalization of the electric field intensity is the precondition for obtaining the defect-induced laser damage threshold accurately.In this paper,the high-transmittance and high-reflection characteristics of splitter films at different wavelengths are used cleverly.The splitter at 355 nmHR and 532 nmHT are designed.Typical damages at the reflection wavelength(355nm)and the transmission wavelength(532nm)are studied.The depth of damage is the distribution of the electric field is correlated,and the normalized electric field at the defect is achieved.Accurate measurements characterize the damage threshold of the defect in the thin film element.It is considered that the laser damage happens exactly at the end of the pulse during the measurement of the pulsed laser damage threshold.The corresponding peak power density cannot be accurately expressed by the laser damage threshold measurement when the laser damage occurs before the end of the pulse.In this paper,we have completed the study of the temporal and spatial resolution laser damage threshold test method for such problems.Set the test method for the laser damage threshold under the condition that the test surface area of the optical element and the sampling rate are extremely small.This method accurately determines the exact time and space coordinates of the laser damage point,and combines the time and space energy distribution of the gaussian pulse laser.So that the laser energy absorbed by each laser damage point during laser damage can be accurately calculated.And set the lowest laser damage energy density as the laser damage threshold of the test sample.