Characteristic of laser induced tungsten plasma in air as a function of laser energy

The laser induced plasma (LIP) of tungsten in air is studied by space resolved laser induced breakdown spectroscopy. Several atomic and ionic lines are identified from the LIP emission of tungsten. The emission intensity increases up to a certain distance from the target surface and then starts to decrease. The ionic lines acquire maximum value of intensity nearer to the target surface than the atomic lines. The two important plasma parameters i.e. plasma temperature and electron density estimated through Boltzmann plot and stark-broadened profile of WI lines respectively. The plasma temperature as well as electron density both increases away from the target surface up to 2 mm distance and then start to fall down. Due to the thermal conduction towards the solid target and radiative cooling of the plasma as well as conversion of thermal energy into kinetic energy, the electron temperature decreases both at the plasma edge and close to the target surface. Both these plasma parameters are also studied as function of laser energies. The validity of the assumption of local thermodynamic equilibrium (LTE) and self-absorption are also verified in the present case. (author)