Characteristics of plasma heating by short-wavelength excimer laser radiation

Various x-ray spectroscopic methods were used to investigate a plasma generated by the interaction of short-wavelength excimer laser radiation pulses (12 ns, 0.308 μm, 4·10-12 W/cm2) with flat targets. A comparison of the profiles and intensities of a number of observed spectral lines of the H-like, He-like, and Li-like sodium, magnesium, and aluminium ions with the results of the reported calculations made it possible to determine the spatial distributions of the laser plasma parameters up to distances of ∼0.4 mm from the target surface. These parameters were compared with the predictions of a simple theoretical model of the absorption of short-wavelength radiation in a plasma. This showed that the absorption of such radiation (with the intensities used in this investigation) involved inverse bremsstrahlung in regions with an electron density much lower than the critical value.