Optical properties of an EMI K2CsSb bialkali photocathode

Abstract A measurement of the angular and polarisation dependence of the reflectance of an EMI 9124B K 2 CsSb bialkali photocathode, with the photomultiplier immersed in water, has allowed an unambiguous determination of the K 2 CsSb complex refractive index (2.7 ± 0.1 + i(1.5 ± 0.1) at 442 nm wavelength) and thickness (23 ± 2 nm). The wavelength dependence of the refractive index has been obtained from a re-analysis of “three intensities” data from Timan [H. Timan, Optical characteristics and constants of high efficiency photoemitters, Revue Technique Thomson-CSF 8 (1976) 49]. A detailed study of K 2 CsSb optical properties (absorptance, reflectance and transmittance) has been performed using the above results as reference points.