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The evolution features of lithium ions and neutrals generated by two different schemes viz. the laser-blow-off (LBO) of multicomponent LiF–C thin film and conventional laser ablation (referred here as LPP) from solid lithium have been studied using optical emission spectroscopic technique. The optical signal emitted by Li I (at 670.8 nm) and Li II (548.4 nm) was monitored as a function of laser fluence, ambient gas pressure, and distance “z” from the target. Apart from their similarities, some interesting differences were noticed in temporal profiles of the plumes generated by LPP and LBO both in vacuum as well as in the presence of the ambient gas. A comparative analysis of experimental results indicates that the ablation mechanism and subsequent laser-plume interaction were responsible for the observed differences in LPP and LBO plumes. Expansion features of the plume are discussed in the light of two different models.

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A corona model is used in analyzing the Doppler shifted spectroscopy (DSS) data for estimating the ion species mix and beam species fractions in positive ion based neutral beam injectors. In this model the excited neutral atom is assumed to decay solely by a spontaneous radiative process. However, at the beam energies of 20–60 keV/amu, collisional quenching of the excited neutrals affects these estimations when background pressure exceeds 1 mTorr. We present here a modified corona model that takes into account the effects of collisional quenching. We also describe the results of application of the present model to a typical DSS data obtained in the first phase of operation of the SST-1 neutral beam injector.