Research On The Damage Mechanism Of 532nm Laser To Gallium Arsenide Materials And Photocathode

With the rapid development of the field of accelerators,high average power free electron laser(FEL),energy recovery linear accelerator(ERL),and electronic cooling have put forward very high requirements for photocathodes,such as high quantum efficiency,low emittance and long life.As an excellent photoelectric emitter,GaAs has higher quantum efficiency and lower emittance than traditional photocathodes.GaAs photocathode is very harsh in terms of its lifetime.Laser irradiation is one of the key factors determining the lifetime of GaAs photocathode.At present,there are many correlative analyses of laser damage to GaAs,but there are still some deficiencies in the damage analysis of GaAs cathode.In order to explore the damage mechanism of laser on GaAs cathode,the theoretical analysis was carried out by modeling and software verification.Finally,the damage mechanism of GaAs material and GaAs cathode during irradiation was analyzed by experimental verification.Firstly,collect the physical parameters of GaAs material,clearly understand the changes of its parameters when the temperature changes,and fit the parameters with function.Through theoretical deduction,the absorption coefficient,reflection coefficient and reflectivity of GaAs material are calculated,and compared with the correlation coefficient of GaAs material and measured GaAs cathode.Temperature field of GaAs irradiated by laser was modeled based on heat conduction equation,and transient heat transfer model was established based on transient heat transfer.At the same time,the theoretical analysis of the model is carried out based on the principle of laser-material interaction.The hot-melt damage threshold of GaAs is deduced and calculated to be about 18.165MW/cm2.The hot-melt damage threshold of GaAs is19MW/cm2 obtained by software simulation analysis combined with finite element method.The difference between the two results is compared and a reasonable error analysis is made.The damage mechanism of GaAs cathode by laser irradiation was improved by combining thermal stress and adsorption desorption theory.The relationship between the loss of activated cesium oxide layer on the surface of GaAs cathode with negative electron affinity and the attenuation of cathode performance and quantum efficiency was analyzed.Combined with software simulation and experiment,the thermal conductivity of GaAs cathode bracket laser irradiation was optimized and improved,and the test was up to the standard.The damage of GaAs cathode caused by quasi-CW 532nm laser and nanosecond pulsed 532nm laser at the same average power was compared.The thermal damage threshold of GaAs cathode was measured by laser irradiation in the atmosphere.Under the above threshold power,the prepared GaAs cathode was irradiated by laser in an electron gun.The loss of GaAs cathode by laser at high power density was observed and recorded.The range of a laser power density threshold was found when laser irradiated GaAs cathode resulted in the complete desorption of cesium oxide layer on the surface.The results of this study can provide a reference for further study on the mechanism of laser damage to GaAs cathode,and provide a basis for the selection of laser power for GaAs cathode irradiation.