Mg-based Photocathodes Prepared By Ns, Ps And Fs Pld For The Production Of High Brightness Electron Beams

摘要

Mg-based films have been prepared by pulsed laser deposition technique for photocathode applications. We have investigated the influence of pulse laser duration on morphology and photoemissive properties. Two laser sources have been used, generating pulses of 30 ns at 308 nm (XeCl excimer laser), 5 ps and 500 fs at 248 nm (KrF excimer laser) to grow Mg films onto Si and Cu substrates in high vacuum (～10~(-7)Pa) and at room temperature. Morphological investigations carried out by scanning electron microscopy (SEM) have revealed that, in our experimental conditions, the number and the mean size of the droplets on the films surfaces decreases as the pulse laser duration shortens. The contamination level of Mg film surfaces have been studied by energy dispersive X-ray spectroscopy (EDX). The photoelectron performances in terms of quantum efficiency (QE) and emission stability have been tested in a UHV DC photodiode cell (10~(-7) Pa). Measures of the QE of the samples surfaces have revealed a decrease on the initial value for Mg-based photocathodes prepared by fs laser (from 7.8 × 10~(-4) to 6.6 × 10~(-4)) PLD with respect to ps (from 6.2 × 10~(-4) to 7.4 × 10~(-4))andns lasers (from 5.0 × 10~(-4) to 1.6 × 10~(-4)). A comparison among Mg-based photocathodes prepared by ns, ps and fs PLD for the production of high brightness electron beams has been presented and discussed.