Quantum efficiency and stability of alkali halide UV photocathodes in the presence of electric field

It was shown previously that CsI sensitivity can be substantially reduced by intense UV irradiation. In the present study we measure the influence of negative and positive electric fields on the degradation of CsI photocathode sensitivity when it is subject to a large dose UV irradiation. The UV sensitivity of positively biased CsI photocathodes did not decay as fast as in case of negatively biased films. Thus we found that negative (photoelectron-extracting) electric field not only increases quantum efficiency of CsI photocathodes (as reported previously by Buzulutskov et. al., J. Appl. Phys. 77 (1995) 2138), especially at long wavelengths, but also substantially reduces the long term performance of the photocathode under intense UV irradiation. Electron-repelling electric field (generally used in MCP detectors with opaque photocathodes), on the other hand, significantly reduces aging of the photocathode under UV irradiation.