Characterization of a Laser Plasma in a Pulsed Magnetic Field. Part II: Time-Resolved Emission and Absorption Studies

Abstract

Temporally resolved emission and absorbance measurements were made in order to investigate the dynamic effects of a high-intensity pulsed magnetic field on a laser plasma. Temporally resolved emission studies were spatially resolved so that the effects of the magnetic field on plasma propagation both along and normal to the magnetic field could be probed. The mechanism of interaction of the field was investigated by observing plasma emission in spatial zones most likely to be influenced by an induced secondary current in the plasma. Spatial and temporal discrimination of emission enhancements indicated that radial compression was due to static magnetic field interactions with the laser plasma and that mild Joule-heating from the small induced current was most likely responsible for emission enhancements later in time. Spatially integrated absorbance measurements in the decaying plasma showed a decrease in absorbance as a result of the magnetic confinement; this is attributed to an increased rate of condensation of the atoms in the vapor cloud produced by the pinched plasma. More efficient coupling of energy from the magnetic field to the plasma would require low-pressure operation in a controlled atmosphere and/or a pulsed magnetic field having a greater d B/d t.

Enhancement of LIBS signal by spatially confining the laser-induced plasma

“…The confinement of the laser plume in a steady or pulsed magnetic field was first proposed. 11 The maximum enhancement factor achieved by the technique was a factor 2, while Zeeman broadening of spectral lines and possible line shifts due to multiplet splitting are its main limitation. It is well known that the formation and expansion of laserinduced plasma in a gas is accompanied by the formation of a shock wave.…”

Physics of Plasma in Laser-Induced Breakdown Spectroscopy

“…Various techniques have been used to improve the sensitivity of LIBS, such as oblique incidence of laser on the sample surface [84], introduction of purge gas around the plasma [103][104], application of pulsed and dc magnetic field [105][106][107][108] as well as double laser pulse excitation of plasma [109][110][111][112]. Mason and Goldberg [105][106] used tens of kilogauss pulsed magnetic field for enhancing the emission from laser produced plasma by 2-5 times. An enhancement of 1.5-2 times in the emission from the laser produced plasma was obtained by Rai et al [107][108] using a steady magnetic field of ∼5-6 kG.…”

The application of magnetic field at low pressure for optimal laser-induced plasma spectroscopy

“…Due to the long range of electromagnetic forces, each charged particle in the plasma interacts simultaneously with a considerable number of other charged particles, resulting in the collective effects that are responsible for the wealth of physical phenomenon that takes place within the plasma [6]. In any means, the magnetic confinement causes not only the conversion of a kinetic energy of the plasma into a thermal energy [7,8], but also the increase of both effective density and the rate of electron recombination in the plasma [6,9,10]. Therefore, the collective effects of these phenomena are expected to enhance significantly the emission intensity during the laser-induced plasma spectroscopy [11,12].…”