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

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. [ABSTRACT FROM AUTHOR]