Spectroscopic investigations of the laser induced thallium plasma

Abstract

Laser-induced breakdown spectroscopy has been used for the spectroscopic characterization of thallium (Tl) plasma, produced using the fundamental harmonic of a Q-switched Nd:YAG laser. The optical emission was recorded in the spectral range of 200–720 nm using a set of five miniature spectrometers with 2.5 μs delay time and 2.1 ms gate width. The plasma temperature was determined using the Boltzmann-plot method, and the electron number density was deduced from the Stark broadened line profile of Tl (I) 322.97 nm line. The plasma temperature and electron number density have been evaluated as a function of laser irradiance (5.2 × 1010 to 8.2 × 1010 W cm−2) which increases from 11 450–13 780 K and (5.2–6.2) × 1017 cm−3 respectively. The spatial profile of these parameters shows a decreasing trend from 13 000–7600 K and (6.3–5.8) × 1017 cm−3 along the plume expansion length up to 2.5 mm from the target surface. The spatial behavior of the plasma parameters has been discussed in relation to the reported temporal trend to indicate inter-relation of the spatio-temporal profile of the laser induced plasma.