Quantum efficiency of technical metal photocathodes under laser irradiation of various wavelength

TL;DR

This study investigates the quantum efficiency of various metal photocathodes under laser irradiation at different wavelengths, revealing multi-photon emission below work function and long-term QE improvement without degradation.

Contribution

It provides new insights into the behavior of technical metal photocathodes under laser irradiation, including multi-photon effects and long-term QE stability.

Findings

Electron emission occurs below the work function due to multi-photon absorption.

No QE degradation observed; long-term irradiation can improve QE.

Contrasts with RF photogun observations.

Abstract

Quantum efficiency studies for various wavelength and various technical metal surfaces were carried out in a dedicated unbaked vacuum chamber. Copper, magnesium, aluminium and aluminium-lithium photocathodes were irradiated by two different high power, high repetition rate, laser systems. We have observed an emission of electrons for photon energy below the work function of the material. This is explained by multiple photon absorption at the photocathode. We have not observed any degradation of the QE for those materials, but an improvement when irradiating them over a long period of time. This is contrary to observations made in RF photoguns.