Measurements of Laser Absorption and Ion Energy in Femtosecond Laser--Cluster Interaction

Laser absorption is measured in Xe, Ar and He clusters irradiated by 5 mJ laser pulses in 150 fs. The measurements show that the absorption efficiency strongly depends on the backing pressure of the gas jets, the laser pulse duration and the atomic number Z of the working gas. The laser absorption for Xe clusters is found to be as high as 45% at a backing pressure of 20 atm and a laser intensity of 1 x 10¹⁵ W/cm². Significant numbers of ions with energies up to 100 keV are detected from Xe cluster explosion. The variation trend of the average ion energy at different backing pressures is consistent with that of the laser energy absorption.