Nitrogen laser beam interaction with copper surface

The ultraviolet and visible spectra of plasmas produced by N_2-laser radiation focused onto a copper target in air and in vacuum have been recorded photographically. The nitrogen laser beam (α = 337 nm) had a maximum energy density of 1.1 J/cm^2, the pulse duration was 6 ns, and the repetition rate 0.2 Hz. The measured electron temperature was 15000 K (±30%) in air and 13000 K (±50%) in vacuum and the electron densities were 6.5×10^17 cm^-3 (±60%) and 3.0×10^17 cm^-3 (±60%), respectively. The irradiated surface in air and in vacuum was studied employing a metallographic microscope. In vacuum, the droplets were created and expulsed at the crater edges. Their formation is explained by the hydrodynamical model. They were formed in a time interval which is about two times shorter than the duration of the laser pulse. In air, droplets were also formed. The weight loss from the Cu-crater in vacuum was about 0.3×10^-4 µmole/pulse, in air it was about three times less