Experimental investigation of oscillatory structures in laser-blow-off plasma plume

Temporal evolution of the floating potential of the laser-blow-off plasma plume and its variation with experimental conditions is studied using a triple Langmuir probe. Findings indicate that oscillatory structures are formed in the trailing portion of the plume in vacuum and their amplitudes vary with axial distance, laser fluence and ambient gas pressure. Spectral analysis suggests that an acoustic wave of specific frequency and phase velocity propagates. The neutral density gradient in the laser-blow-off plasma plume and its equilibration might be responsible for the above phenomenon.

► Laser-blow-off (LBO) plasma plume of LiF-C film is formed.
► Oscillatory structure in the floating potential is observed in the plume.
► Amplitude of oscillation depends on the experimental parameters.
► Frequency of oscillations corresponds to acoustic wave.
► Neutral density gradient is proposed as the source of oscillations.