TITLE:
Spectrometric Measurement of Plasma Parameters Utilizing the Target Ambient Gas O I & N I Atomic Lines in LIBS Experiment
AUTHORS:
Ashraf M. El Sherbini, Abdel Aziz Saad Al Amer, Ahmed T. Hassan, Tharwat M. El Sherbini
KEYWORDS:
LIBS; Self Absorption; O I-N I Lines; Plasma Parameters
JOURNAL NAME:
Optics and Photonics Journal,
Vol.2 No.4,
December
28,
2012
ABSTRACT: In this article, we shall report the results of the
spectroscopic measurements of the plasma parameters utilizing the spectral
lines emitted from the air atoms surrounding plasma (O I line at 777.19 nm and
N I at 746.83 nm). The plasma was created via irradiation of plane solid
aluminum target in open air by a high peak power Nd: YAG laser pulses at fundamental
wavelength of 1064 nm. The emission spectra were recorded using Echelle type
spectrograph in conjunction with a time gated ICCD camera at different delay
time from 1 to 5 μs and at a fixed gate time of 1 μs. The plasma electron
density was measured utilizing the Stark broadening of the N I and O I lines
and then compared to the reference density as deduced from the optically thin Hα-line at 656.27 nm appeared
in the same emission spectra. The results show that under our experimental
conditions the air lines are subjected to moderate absorption. The plasma electron
temperature was measured utilizing the relative spectral intensity of the air
(O I to N I) lines after correcting their spectral radiance against absorption.
The standard temperature was measured utilizing the Al II ionic lines. A comparison
to the reference temperatures shows a very close agreement after correcting the
emission spectral radiance of the air lines against self absorption, which
emphasizes the importance of correction process.