engleski

Spectral line enhancement in laterally colliding boron-nitride

Line intensities in laterally colliding boron-nitride (BN) plasmas were compared to the line intensities in non-colliding BN plasmas. The plasmas were produced by splitting the laser beam from 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 on target) was focused into the rectangular groove cut into the target surface in order to compensate for the higher expansion velocity of the hot plasma. The cold plasma was produced by the weaker part of the laser beam (1J, 500 J/cm^2 on target) that was focused onto the target surface nearby. The plasma spectra in the spectral region between 16 and 34 nm were registered with a VUV spectrograph equipped with a gateable multichannel plate (MCP) and CCD camera. Due to the low intensity of the lines, the acquired spectra are time-integrated. The spectrum of the colliding plasmas is compared to the sum of the separately produced hot and cold plasmas. 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-half in the colliding plasmas. The only exception was the Balmer-alpha line of B V, which showed a little enhanced intensity in the colliding plasmas. This effect is interpreted as a sign of the charge-exchange mechanism that was observed before in colliding carbon plasmas, and for which the theoretical calculations indicate a reasonably large cross-section.

colliding BN plasmas; ruby laser

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