Research on optical properties of transmission-mode GaAs photocathode module

In order to know performance of transmission-mode photocathode module completely, the GaAs photocathode with a structure of Glass/Si 3 N 4 /Ga 1-x Al x As/GaAs was prepared in the experiment and the reflectance and transmittance spectra were measured by the spectrophotometer. Meanwhile optical constants of the GaAs active layer and the Ga 1-x AlxAs window layer in the photocathode are discussed by using piecewise polynomial fitting method. On this basis of analysis on the optical constants, the theoretical reflectance, transmittance and absorptivity of cathode module are calculated and revised with the aid of matrix formula in thin film optics. The thickness of each layer in the module is obtained by fitting the reflectance and transmittance curves simultaneously. The results indicates that the thicknesses of three thin films except Glass are respectively 110.14 μm, 1007.20 μm, 1480.81 μm with the relative curve error less than 5%, meanwhile the error of the module thickness in total is also controlled within 5%.