Effect of Ar and O 2 Atmospheres on the Fundamental Properties of the Plasma Produced by Laser Ablation of Lithium Niobate

Abstract

The influence of gas atmospheres (at 1 torr) of different natures, both reactive (O₂) and inert (Ar), on the spatial evolution of the electron temperature (T_e) and electron density (N_e) of the plasma generated by laser ablation of a LiNbO₃ target is evaluated by optical emission spectroscopy techniques. It is found that the behavior of N_e in the plasma produced in vacuum, argon, and oxygen atmospheres exhibit quite different trends as a function of the distance from the target to the substrate, but the behavior of T_e is nearly constant. The spatial constancy of T_e in all the atmospheres studied is probably related not only to the low laser irradiance used (0.06 GW cm⁻²), but also to a possible collisional decoupling of the heavy species in the central part of the expanding plasma plume where a low pressure region is formed. The fact that N_e is lower in Ar than in O₂ indicates the presence of fewer positive ions in the plasma generated in Ar. The impact of this result on the better crystallinity observed in the LiNbO₃ films grown in Ar is also discussed.