Electron beams induced by excimer lasers on metal targets

This work reports on the experimental results concerning electron beam emittance and current photo-extracted from aluminium, zinc and copper targets utilising two excimer lasers of different wavelengths, 308 nm (XeCl) and 222 nm (KrCl). The maximum laser energies utilised were limited by the high plasma density on the cathode that short-circuited the diode gap. The output current was higher with the KrCl laser than with the XeCl laser for the three metals used. The maximum extracted current, 1.03 A, was obtained with Cu targets at 20 kV of accelerating voltage, while at the same acceleration voltage a computer simulation of a space-charge limited electron beam resulted in a total current of only 200 mA and a normalised emittance of 22π mm mrad. The output current for large anode-cathode distance was higher than that predicted by the Child-Langmuir law while for small distances the current was lower than that theoretically calculated. This behaviour was attributed to plasma formation on the cathode during the laser action.