Effect of transverse magnetic field on the laser-blow-off plasma plume emission in the presence of ambient gas

In the present paper we report the effect of variable magnetic field in the range of 0.04–0.2 T on the emission of two neutral Lithium lines Li I 670.8 nm and Li I 610.3 nm and one ionic line Li II 548.4 nm in the presence of ambient gas on the laser-blow-off plasma plume. Enhancement in the intensity associated with structures was observed in the temporal profile of neutrals, which is strongly dependent on the magnetic field intensity, distance from the target and background gas pressure. At 6 mm distance and 1.33 Pa argon pressure, apart from overall enhancement in the intensity of both the neutral lines, the results reveal some interesting features, e.g. disappearance of structures and narrowing of the temporal extent of 670.8 nm line at higher magnetic fields. On the other hand, the 610.3 nm line exhibits a significant enhancement in the intensity at the trailing part as the field is increased. At a shorter distance (2 mm) and for relatively higher pressures (133.3 Pa), the effect of field is not much prominent. Interestingly, the ionic spectral line does not exhibit any significant change with both, magnetic field and ambient gas.We explain the results by considering the role of various atomic processes viz. electron impact excitation, recombination and diffusion of ambient gas into plume in collisional and hydrodynamical regimes.