Influence of beam parameters on the laser induced particle emission from surfaces

For analysis of the laser induced plasma from graphite targets in high vacuum time-of-flight velocity distributions of ablated carbon ions have been measured. The previously observed linear relation between ion energy and laser energy density in the regime of nanosecond laser pulses is confirmed. Moreover, an enhancement of the laser spot size on the target results in higher kinetic ion energies in the same way as an increase of the laser energy density, being in accordance with standard ablation theories. The use of femtosecond laser pulses (500 fs, 248 nm) results in strongly enhanced kinetic energies of up to 10 keV at about 9 J/cm(2), as compared to 50 eV at similar energy densities in the ns regime.