Spectroscopic study of carbon plasma produced by the first (1064 nm) and second (532 nm) harmonics of Nd:YAG laser

In this research work, spectroscopic studies of carbon (C) plasma by using laser-induced breakdown spectroscopy (LIBS) are presented. The plasma was produced by the first (1064 nm) and second (532 nm) harmonics of a Q-switched Nd:YAG (Quantel Brilliant) pulsed laser having a pulse duration of 5 ns and 10-Hz repetition rate, which is capable of delivering 400 mJ at 1064 nm and 200 mJ at 532 nm. The laser beam was focused on the target material (100% carbon) by placing it in air at atmospheric pressure. The experimentally observed line profiles of five neutral carbon (C I) lines at 247.85, 394.22, 396.14, 588.95, and 591.25 nm were used to extract the electron temperature T_e by using the Boltzmann plot method and determine its value, 9880 and 9400 K, respectively, for the fundamental and second harmonics of the laser, whereas the electron density N_e was determined from the Stark broadening profile of neutral carbon line at 247.85 nm. The values of N_e at a distance of 0.05 mm from the target surface for the fundamental-harmonic laser with a pulse energy of 130 mJ and the second-harmonic laser with a pulse energy of 72 mJ are 4.68 × 10¹⁷ and 5.98 × 10¹⁷ cm⁻³, respectively. This extracted information on T_e and N_e is useful for the deposition of carbon thin films by using the pulsed laser deposition technique. Moreover, both plasma parameters (T_e and N_e) were also calculated by varying the distance from the target surface along the line of propagation of the plasma plume and also by varying the laser irradiance