Spectroscopic studies of laser induced aluminum plasma using fundamental, second and third harmonics of a Nd: YAG laser

In the present work, we have studied the spatial evolution of the aluminum plasma produced by the fundamental (1064 nm), second (532 nm) and third (355 nm) harmonics of a Q-switched pulsed Nd:YAG laser. The experimentally observed line profiles of neutral aluminum have been used to extract the excitation temperature using Boltzmann plot method whereas the electron number density has been determined from the Stark broadened profiles. Besides we have studied the variation of excitation temperature and electron number density as a function of laser irradiance at atmospheric pressure. In addition, we have performed quantitative analysis of photon absorption and vapor ionization mechanism at three laser wavelengths and estimated the inverse bremsstrahlung (IB) absorption and photoionization (PI) coefficients. The validity of the assumption of local thermodynamic equilibrium is discussed in the light of the experimental results.