M. Anwar-ul-Haq

Spatial diagnostics of the laser induced lithium fluoride plasma

We present spatial characteristics of the lithium fluoride plasma generated by the fundamental and second harmonic of a Nd:YAG laser. The plume emission has been recorded spatially using five spectrometers covering the spectral region from 200 nm to 720 nm. The electron density is measured from the Stark broadened line profile of the line at 610.37 nm, whereas the plasma temperature has been determined using the Boltzmann plot method including all the observed spectral lines of lithium. Both the plasma parameters; electron density and plasma temperature decrease with the increase of the distance from the target surface. The thermal conduction towards the target, the radiative cooling of the plasma, and the conversion of thermal energy into kinetic energy are the main mechanisms responsible for the spatially decrease of the plasma parameters.

On the first ionization potential of lithium

New experimental data on the highly excited Rydberg states of lithium have been acquired, using a two-step laser excitation technique in combination with a thermionic diode ion detector. The atoms are prepared in the 3s 2S1/2 intermediate level by two-photon excitation from the ground state, whereas the np 2P1/2,3/2 levels have been approached via single photon absorption. The new observations include much extended np 2P1/2,3/2 Rydberg series (15 ? n ? 60). The Rydberg relation fit to the new data yields the quantum defect for the np 2P1/2,3/2 series as 0.051(4) and the binding energy of the 3s 2S1/2 level as 16?281.19(2) cm?1. Adding the energy of the 3s 2S1/2 level and its binding energy reveals the first ionization potential of lithium as 43?487.26(3) cm?1.