Spectral response characteristics of transmission-mode alkali telluride photocathodes working from vacuum-ultraviolet to ultraviolet band

Abstract

In order to characterize the spectral response of transmission-mode alkali telluride photocathodes, a spectral response measurement system for image intensifiers working from the vacuum-ultraviolet to ultraviolet band is developed. Using this system, the transmittance curves of usual window materials such as quartz, MgF2, and sapphire selected to prepare alkali telluride photocathodes are measured. In addition to the transmittance test function, the spectral response of image intensifiers based on transmission-mode alkali telluride photocathodes, such as Cs2Te, Rb2Te, Cs-K-Te, and Rb-K-Te photocathodes, under the excitation light from 115 to 400 nm is measured. The measured results show that the longwave cutoff wavelength of the Rb2Te photocathode is 313 nm, while that of the Cs2Te photocathode is 342 nm, which could be ascribed to the reduced cathode work function, inversely proportional to the atomic number of the alkali element in uni-alkali telluride photocathodes. Besides, the spectral response values of Cs-K-Te and Rb-K-Te photocathodes are greater than those of Cs2Te and Rb2Te photocathodes, and this case is similar to the multialkali effect of alkali antimonide photocathodes. The cutoff wavelength can get shorter through the combination with an additional K element. Compared with the Rb-K-Te photocathode with the shorter cutoff wavelength, the Cs-K-Te photocathode can achieve higher sensitivity.