Study of magnetic confinement in laser-induced plasmas by optical emission spectroscopy and fast photography

The dynamics and magnetic confinement effects of laser-induced plasmas expanding across an external transverse magnetic field were investigated by both optical emission spectroscopy and fast photography. KrF excimer laser pulses with a pulse duration of 23 ns and a wavelength of 248 nm were used to produce plasmas from Cu targets. Various optical emission lines show an obvious enhancement in the intensity of optical emission when a magnetic field of 0.8 Tesla is applied. Temporal evolution of the optical emission lines shows a continuous enhancement in emission intensity at time delays of 3-20 μs after the incident laser pulse. The enhancement in the optical emission from the Cu plasmas was presumably due to the increase in the effective plasma density as a result of magnetic confinement. Fast photography of the laser-induced Cu plasmas was performed using a Nikon macro lens and Andor intensified CCD camera. It shows that the plasma splits into two parts after gate delay of around 4 μs both with and without a magnetic field. With the presence of a magnetic field, the two parts of the plasma were confined and recombined with each other after gate delay of around 18 μs. While without the presence of a magnetic filed, the two parts kept separated as gate delay increased.