Servizio Comunitario di Informazione in materia di Ricerca e Sviluppo - CORDIS

The theory and prediction of the quantum efficiency and wavelength dependence of shaped photocathodes

Theoretical modelling of the performance of the S20 photocathodes has been made with input from the measured dielectric constants. For the planar photocathodes there is a close match in terms of the predicted a priori absolute quantum efficiency and the standard tube data. The evaluations extend to include the angular dependence of the optical absorption, polarisation effects, the effect of ridges, cones and other structures on the cathode substrate, and the results of using waveguide geometries to enhance cathode performance.

The developments of the theory have been matched with experimental data in many cases and there are good agreements. The fundamental aspects of the work have been published, or are in print. The same theoretical approach also predicted the observed reflectivity data seen for “black silicon”. Commercially sensitive predictions have been retained but used in modelling of new tube designs and retrofits.

The theory has included both quantum mechanical and simplistic alternatives. The former approach has been necessary to evaluate the way in which electrons interact with the cathode-vacuum surface and their probability of escape as a function of incident wavelength. This latter feature is a major consideration for long wavelength improvements in sensitivity.

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University of Sussex
EIT, Pevensey Building
BN1 9QH Brighton
United Kingdom