| In large-energy,high-power solid-state laser devices,a large number of vacuum optical windows are required to shield the vacuum environment and transmit the laser beam.When subjected to the same laser flux,the vacuum optical window is more prone to damage than other optical components,and the damage develops more rapidly under multiple irradiations,and even windows cracking occurs.Therefore,the damage of the vacuum optical windows is an important problem facing the design and operation of the current laser device.According to the inherent environment and structural characteristics of the vacuum optical windows,stress is the most basic and most critical factor affecting its laser-induced damage.Therefore,this paper mainly studies the effect of stress load on the laser-induced damage threshold and damage growth of vacuum optical windows.When the optical windows are fixed by a flange,and the system is in an atmospheric environment,the influence of flange clamping stress on laser-induced damage is studied.When the air pressure in the vacuum system is 10-3 Pa,the windows are fixed on the vacuum pipe by the air pressure difference on both sides of the window,and the influence of the stress caused by the air pressure difference on the laser-induced damage is studied.The window stress distribution is obtained through finite element analysis,and the area with close stress values(six irradiation positions,in a ring shape)is selected for laser irradiation,and the diameter of the spot is about 8 mm after focusing.The stress-induced damage threshold and damage growth experiment of K9 glass window under 1053 nm laser and fused silica window(Corning 7980)351 nm laser irradiation were carried out.The experimental results in this paper show that when the K9 window is subjected to a certain flange clamping stress,its laser-induced damage threshold is reduced by 47%compared with the unstressed condition,and small cobweb-like cracks appear at the damage location.In the multiple damage experiment of the flange clamping window,no obvious changes were observed in the damage of pits with a diameter of several micrometers under subsequent laser irradiation;the size of the damage pits with a diameter of tens of micrometers increased significantly,which caused serious damage to the window.When the fused silica window is subjected to flange clamping stress(bolt torque7 N·m),its laser-induced damage threshold is reduced by 27%compared with the unstressed condition.There is no difference in the damage morphology of the window under different stress conditions,but the damage growth of different forms is different.Part of the pitting damage did not change significantly in size after several times of irradiation,and some pitting damage areas showed mussel-like damage and volcanic pit-like damage.However,the size of these two kinds of damage has increased significantly,and the window has been damaged or even cracked in a large area after multiple irradiations.Only when the window was subjected to flange clamping stress,cracks appeared.The radial cracks that appear after the initial damage after multiple laser irradiations continue to grow.When the length reaches a subcritical state(300-400?m),the next laser irradiation may make it reach a critical state,and the cracks continue under stress Growth eventually runs through the entire window.This is mainly caused by the growth of radial cracks in the direction of maximum stress gradient caused by laser damage.Under no stress condition and stress condition caused by air pressure difference,the window will also appear radial cracks after multiple laser irradiations,but gradually turn into circumferential cracks,without window cracking.This paper explores the influence of stress on the laser-induced damage threshold and damage growth of vacuum optical windows,which provides a reference for studying the damage behavior of vacuum windows. |
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