Influence of ambient gas and its pressure on the laser-induced breakdown spectroscopy and the surface morphology of laser-ablated Cd

Abstract

The ablation of Cd has been performed by employing Q-switched Nd: YAG 10 ns laser pulses with a central wavelength of 1064 nm for a pulsed energy of 200 mJ under various ambient environments of argon, air and helium. The optical emission spectroscopy of Cd plasma has been studied under different filling pressures of shield gases ranging from 5 torr to 760 torr using LIBS spectrometer system. The effect of different gases and their pressures on the intensity of spectral emission, electron temperature and density of the laser-produced plasma has been investigated. SEM analysis has been performed to investigate the dependence of surface morphological changes of an irradiated target on the nature and pressure of an ambient gas. A strong correlation has revealed the vital role of electron temperature and density of laser-induced plasma for the surface modification of Cd. These results strongly indicate that the nature and pressure of the ambient atmosphere is one of the controlling factors of the plasma characteristics, as well as the factors related to the laser energy absorption for surface modification.

Effect of ambient gas pressure and nature on the temporal evolution of aluminum laser-induced plasmas

“…This contrasts with the results reported by Iida, 5 Asimellis et al, 15 and Knight et al 16 and N. Farid et al, 22 who observed a maximum excitation at some finite pressure. The authors attribute such a trend to the interaction of the plasma with the ambient gas where the later acts as an energy buffer transferring a fraction of its energy to the Al plasma in low pressure while at high pressure, collision of electrons with gas atoms increases so that the cascade condition is not favoured and the electron density consequently decreases.…”

“…They attribute these results to the interaction between plasma plume and ambient gas. 5,[16][17][18] It can therefore be concluded from these various observations that there is no clear consensus on the dependence of ablation plasmas on their environment. In this context, the primary objective of the present work is to conduct a deep study of the interplay between the ablated plasma plume and the ambient gas by analyzing the temporal evolution of an Al-plasma in terms of spectral intensity, electron density and excitation temperature within various environments extending from vacuum to atmosphere, and using inert gas like Ar and He as well as chemically active gas like N 2 .…”

Axial- and radial-resolved electron density and excitation temperature of aluminum plasma induced by nanosecond laser: Effect of the ambient gas composition and pressure

“…They found that n e and T are maximum at a gas pressure of about 100 Torr. However, another study performed by Bashir et al 16 report a continuous decrease of both n e and T when the ambient gas pressure increases from 5 to 760 Torr during the ablation of cadmium. In our published work, 17 we have shown that, in our conditions, n e and T decrease continuously with the ambient gas pressure ranging from vacuum to atmosphere.…”

“…On the other hand, based on the McWhirter criterion, the higher values of the electron density measured (see hereafter) in our plasma pushes us to assume that our plasma is in local thermodynamic equilibrium (LTE). Under this assumption, the population of excited states follows the Boltzmann distribution which is given by the following relation 15,16,27 :…”

“…14 The temporal evolution and space variation of such parameters have been the aim of several publications. [15][16][17][18][19][20][21] For instance, Farid et al 15 have studied the temporal evolution of the electron density n e (deduced from the Stark broadening of copper line at 578.21 nm) and excitation temperature T (deduced from Boltzmann plot method of Cu lines) of a copper plasma expanding in ambient gas with different composition and pressures. They found that n e and T are maximum at a gas pressure of about 100 Torr.…”