The time-integrated radiant energy from laser-produced and laser-heated breakdown plasmas was spectro-scopically examined. The spectra consisted of a strong continuum with several lines. Band spectra characteristic of molecular species could not be detected in pure diatomic gases. The lines were very broad especially in the same spatial region as that from which the continuum was emitted. Line spectra emitted from outside this region were predominantly from un-ionized atoms. The spectral lines from singly ionized atoms were emitted in a volume only slightly larger than that for the continuum. Photomultiplier-interference-filter measurements of the afterglow indicated that in nitrogen the atom lines last five times as long as do the ion lines. When the peak laser power exceeded 600 MW the spectrum of doubly ionized nitrogen atoms was detected. The absence of molecular spectra and the threshold for the appearance of doubly ionized nitrogen indicate that the plasma may be in a state of total equilibrium at a high temperature.
J. W. DAIBER and J. G. WINANS, "Radiation from Laser-Heated Plasmas in Nitrogen and Argon," J. Opt. Soc. Am. 58, 76-79 (1968)