Diagnostic value of odd-integer half-harmonic emission from laser-produced plasmas

Abstract

The diagostic value of odd-integer half-harmonic emission from laser-produced plasmas is evaluated in the light of recent spectral measurements on UV irradiation experiments. It has been found that under certain conditions a sharp, slightly red-shifted feature is observed in the ω/2 spectra. This feature has been identified with a particular mode of the 2ωp decay instability for which one of the plasmon wave vectors vanishes. This feature is eminently well suited for coronal electron temperature measurements. Another half-harmonic (blue-shifted) feature is more easily observed and may serve as a secondary—though less accurate—temperature diagnostic. In contrast, the spectral splitting of the (3)/(2) harmonic emission proved to be ill suited for temperature diagnostics because of its sensitivity to irradiation and observation geometry. Either ω/2 or 3ω/2 emission is, however, a good qualitative indicator for the presence of the 2ωp decay instability although quantitative inferences on the level of the 2ωp decay instability are not possible at this point.