Electronic temperature and density of the plasma produced by nanosecond ultraviolet laser ablation of LiF

Optical emission spectroscopy is used to investigate the spatial evolution of the electron temperature ( T e ) and electron density ( N e ) in the plasma generated by laser ablation in a vacuum of a wide-band-gap material, such as LiF, with a pulsed 193 nm excimer laser operating at a fluence of 1.5 J cm − 2 close to the threshold. It is found that, whereas N e (in the range of 10 16 cm − 3 ) decreases by a factor of 2 as the distance to the target increases, T e exhibits a sharp decrease (from 1.85 eV to 0.66 eV) between 1 and 2 mm from the target and it remains practically constant for longer distances from the target. These results provide direct measurements of the electron temperature and density during nanosecond laser ablation of LiF.