Measurements of iron plasma parameters produced by a 1064 nm pulsed Nd:YAG laser

A 1064 nm pulsed Nd:YAG laser is used for the ablation of an iron bar sample in air at atmospheric pressure and the laser-induced plasma characteristics are examined. The electron number density of 8.71017 cm-3 in the iron plasma is inferred from the Stark broadened profile of Fe I 376.553 nm averaged with 10 single spectra. In order to minimize relative errors in calculation of the electron temperature, an improved iterative Boltzmann plot method is used. Experimental results show that the electron temperature is 8058 K with a regression coefficient of 0.981 38. Based on the experimental results, the plasma is verified to be in local thermodynamic equilibrium (LTE) and free from self-absorption. Considering the laser photon frequency (2.821014 Hz) is larger than the plasma frequency (8.31012 Hz), the loss of energy due to reflection of the laser beam from the plasma can be assumed to be insignificant. Experiments also demonstrate that the inverse Bremsstrahlung (IB) absorption is the dominant photon absorption process during the laser-plasma interaction, and the corresponding IB absorption coefficient is 0.14 cm-1.