Laser-induced breakdown spectroscopy of aluminum plasma in the absence and presence of magnetic field.

ABSTRACT

The effect of magnetic field on laser-induced breakdown spectroscopy of aluminum (Al) plasma has been investigated. Al targets were exposed to NdYAG laser pulses at different irradiances ranging from 1 GWcm-2 to 2.7 GWcm-2, under argon (Ar) and neon (Ne) environments at various pressures ranging from 5 torr to 760 torr and at different time delays from 0.42 µs to 9.58 µs. All spectroscopy measurements were performed in the absence and presence of transverse magnetic field of strength 0.9 tesla. When laser irradiance is increased by keeping the pressure (10 torr) and time delay constant (1.25 µs), both excitation temperature (Te) and number density (ne) increase up to certain values. The same trend is observed for Te and ne when the ambient gas pressure of Ar and Ne is increased by keeping the irradiance (1.7 GWcm-2) and time delay constant. At higher irradiances and pressures, saturation is observed, which is attributed to the self-regulating regime of plasma. In the case of time delay, both electron temperature and number density decay exponentially, which is according to the adiabatic expansion model. It is revealed that emission intensity and electron temperature are higher in the presence of magnetic field as compared to the field-free case, which is attributed to magnetic confinement, as well as the joule heating effect. Plasma plume confinement is confirmed by analytical evaluation factor ß. ß is an analytical factor that is the ratio of plasma pressure to magnetic pressure, i.e., ß=Plasma pressureMagnetic pressure. It confirms the validity of magnetic field confinement if ß is less than 1. As the evaluated values of ß are less than 1 for all cases, they confirm the validity of magnetic confinement.