Abstract

Motivated by recent interest in laser graphite ablation for optical-quality diamondlike carbon-film deposition, we took emission spectra from a pulsed KrF (3 x 10⁸ W/cm²) excimer laser-induced plasma plume on the surface of bulk graphite. A 0.3 m spectrograph and an optical multichannel analyzer (OMA) were used. In the visible region the plasma emission was dominated by the D-A swan and C-A DesIandres-d'Azambuja bands of C₂ and the B-X violet band of CN. No evidence of transitions attributable to C⁺, C, C₃, or larger carbon clusters was found. From the band emission intensity, the vibrational temperatures of the radicals were calculated from the Einstein spontaneous emission coefficients with an assumed Boltzmann population distribution. The results from the different transitions of the C₂ swan and CN violet bands all fell within the range of experimental error and uncertainty error in the Einstein coefficients and indicate a vibrational temperature of (13.5 ± 1.3) x 10³ K for both radicals. This excellent agreement makes one believe that the species in the plasma are likely to be in local thermodynamic equilibrium. C2 radical concentration is estimated to be 1 × 10¹⁵ cm⁻³ on the basis of emission intensity and Boltzmann distribution at the above temperature.

© 1990 Optical Society of America