Plasma properties of 355 nm and 532 nm laser-ablated molybdenum target at atmospheric pressure

This paper presents the results obtained in Mo laser ablation experiments performed in air. Two lasers were used: one Nd:YAG AVIA 355-X emitting pulses with 0.205 mJ energy and 25 ns duration in 355 nm, and one Quantronix Hawk-532-40-M emitting pulses with 2.05 mJ energy and 110 ns duration in 532 nm. The Mo targets were fixed to a XY table, controlled by a computer program which moves permanently the table in order to avoid cratering. The plume was imaged by a 4x telescope and the light emission was collected at the image position by a fiber-optic and coupled to a Triax 550 Jobin-Yvon spectrometer. The spectra analysis was performed assuming the Local Thermal Equilibrium approximation and calculating the plasma temperature by using the Boltzmann plot method using neutral Mo spectral lines. The plasma temperature was obtained for different positions along the expansion axis, which allowed obtaining the electron population distribution as a function of the distance from the target. The plasma temperature along the expansion axis allowed evaluating the evolution of the excited states population when the plume expands.