Effects of Laser Pulse Heating of Copper Photocathodes on High-brightness Electron Beam Production at Blowout Regime

TL;DR

This paper investigates how laser pulse heating affects copper photocathodes used in high-brightness electron beam production, highlighting thermal effects, emittance growth, and damage thresholds for optimized laser parameters.

Contribution

It introduces an improved two-temperature model and extended Dowell-Schmerge model to analyze thermal effects and damage thresholds in copper photocathodes under ultrashort laser pulses.

Findings

Thermal emittance and quantum efficiency grow over time during laser pulse heating.

Projected thermal emittance increases as laser radius decreases for fixed charge.

Maximum local laser fluence should be below 40 mJ/cm^2 to prevent cathode damage.

Abstract

Producing high-brightness and high-charge (>100 pC) electron bunches at blowout regime requires ultrashort laser pulses with high fluence. The effects of laser pulse heating of the copper photocathode are analyzed in this paper. The electron and lattice temperature is calculated using an improved two-temperature model, and an extended Dowell-Schmerge model is employed to calculate the thermal emittance and quantum efficiency. A time-dependent growth of the thermal emittance and the quantum efficiency is observed. For a fixed amount of charge, the projected thermal emittance increases with decreasing laser radius, and this effect should be taken into account in laser optimization at blowout regime. Moreover, laser damage threshold fluence is simulated, showing that the maximum local fluence should be less than 40 mJ/cm^2 to prevent damage to the cathode.