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

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 ...

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