Theoretical aspect of enhancement and saturation in emission from laser produced plasma

Abstract

This paper presents a simplified theoretical model for the study of emission from laser produced plasma to better understand the processes and the factors involved in the onset of saturation in plasma emission as well as in increasing emission due to plasma confinement. This model considers that plasma emission is directly proportional to the square of plasma density, its volume and the fraction of laser pulse absorbed through inverse Bremsstrahlung in the pre-formed plasma plume produced by the initial part of the laser. This shows that plasma density and temperature (that means the electron-ion collision frequency ν ei ) decide the threshold for saturation in emission, which occurs for ν ei ≥ 10 13 s -1 , beyond which plasma shielding effects become dominant. Any decrease in plasma sound (expansion) velocity shows drastic enhancement in emission supporting the results obtained by magnetic as well as spatial confinement of laser produced plasma.The temporal evolution of plasma emission in the absence and presence of plasma confinement along with the effect of laser pulse duration are also discussed in the light of this model.

Nanosecond pulsed laser ablation of Ge investigated by employing photoacoustic deflection technique and SEM analysis

“…The vaporization of the target surface starts instantaneously after the impact of the leading edge of the laser beam. The trailing part of the laser beam also interacts with the vaporized plume and enhances further heating and vaporization [18]. Initially the plasma density increases with the increase of laser fluence and attains the maximum value.…”