Effect of magnetic field on laser-induced breakdown spectroscopy of graphite plasma

The effect of transverse magnetic field on laser-induced breakdown spectroscopy of graphite plasma as a function of fluence has been investigated. Graphite targets were exposed to Nd:YAG (1064 nm, 10 ns) laser pulses at various laser fluences ranging from 0.4 to 2.9 J cm−2 under two different environment of air and Ar at a pressure of 150 and 760 torr. A transverse magnetic field of strength 0.5 tesla was employed by using permanent magnets. It is revealed that due to the presence of the magnetic field the emission intensity, electron temperature and number density of graphite plasma have been increased at all fluences and for all environmental conditions. The enhancement in plasma parameters is attributed to magnetic confinement effect and Joule heating effect. Initially by increasing the fluence from 0.4 to 1.5 J cm−2 (in air) and 0.4 to 1.8 J cm−2 (in Ar), the emission intensity, electron temperature and number density have been increased and have attained their maximum values. Further increase in fluence was responsible for the decreasing trend in all plasma parameters. More increase in fluence (beyond 1.8 J cm−2 in case of air and 2.2 J cm−2 in case of Ar) up to a maximum value of 2.9 J cm−2, the saturation or self-sustained regime was achieved, which is responsible for insignificant changes in plasma parameters. The value of plasma parameter “β” was also evaluated analytically, and it was less than one for all conditions (fluences as well as environments), which confirmed the existence of confinement effect.

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