SPECTRAL-LINE ENHANCEMENT IN LATERALLY COLLIDING BORON-NITRIDE PLASMAS

Line intensities in laterally colliding boron-nitride (BN) plasmas wer e compared to the line intensities in non-colliding BN plasmas. The pl asmas were produced by splitting the laser beam from a ruby laser (5J total energy, 30 ns pulse FWHM) with an optical wedge in front of the focusing lens. The stronger part of the laser beam (4J, 2000 J/cm(2) o n target) was focused into the rectangular groove cut into the target surface in order to compensate for the higher expansion velocity of th e hot plasma The cold plasma was produced by the weaker part of the la ser beam (1J, 500J/cm(2) on target) that was focused onto the target s urface nearby. The plasma spectra in the spectral region between 16 an d 34 nm were registered with a VUV spectrograph equipped with a gateab le multichannel plate (MCP) and CCD camera. Due to the low intensity o f the lines, the acquired spectra are time-integrated. The spectrum of the colliding plasmas is compared to the sum of the separately produc ed hot and cold plasma. The nitrogen and boron lines showed different behaviours. The intensity ratio of nitrogen lines in colliding and non -colliding plasmas showed no marked change in line intensities; on the other side, the intensity of boron lines was reduced to about one-hal f in the colliding plasmas. The only exception was the Balmer-alpha li ne of B V, which showed a little enhanced intensity in the colliding p lasmas. This effect is interpreted as a sign of the charge-exchange me chanism that was observed before in colliding carbon plasmas, and for which the theoretical calculations indicate a reasonably large cross-s ection.