Time-resolved optical emission spectroscopic studies of picosecond laser produced Cr plasma

TL;DR

This study investigates how the linewidth of neutral and ionized chromium emissions varies with ambient pressure in picosecond laser-produced plasma, revealing different behaviors and an optimal pressure for minimal linewidth.

Contribution

It provides the first detailed comparison of neutral and ion emission linewidth variations with pressure in picosecond laser-produced Cr plasma, highlighting the need for careful analysis at intermediate pressures.

Findings

Linewidth of Cr II increases monotonically with pressure.

Linewidth of Cr I oscillates at intermediate pressures.

An optimal pressure minimizes neutral linewidth, affecting plasma diagnostics.

Abstract

Time-resolved optical emission spectroscopic measurements of a plasma generated by irradiating a Cr target using 60 picosecond (ps) and 300 ps laser pulses is carried out to investigate the variation in the linewidth ($\delta\lambda$) of emission from neutrals and ions for increasing ambient pressures. Measurements ranging from 10$^{-6}$ Torr to 10$^2$ Torr show a distinctly different variation in the $\delta\lambda$ of neutrals (Cr I) compared to that of singly ionized Cr (Cr II), for both irradiations. $\delta\lambda$ increases monotonously with pressure for Cr II, but an oscillation is evident at intermediate pressures for Cr I. This oscillation does not depend on the laser pulse widths used. In spite of the differences in the plasma formation mechanisms, it is experimentally found that there is an optimum intermediate background pressure for which $\delta\lambda$ of neutrals drops to a minimum. Importantly, these results underline the fact that for intermediate pressures, the usual practice of calculating the plasma number density from the $\delta\lambda$ of neutrals needs to be judiciously done, to avoid reaching inaccurate conclusions.