Heating of buried layer targets by 1 ω and 2 ω pulses using the HELEN CPA laser

Abstract

Targets of plastic with a buried layer of aluminium were heated using the HELEN CPA laser to irradiate one surface of the plastic. The emission spectra from the aluminium were used to infer the conditions in the target by comparing the measured spectra against synthetic spectra generated by the FLY code. The input to the FLY code was the temperature and density history calculated by a radiation-hydrodynamics code, which was iterated to achieve the best match to the experimental data. Aluminium layers at different depths in the plastic were used to measure how heat was transported into the target. Measurements were taken with the laser at wavelengths of 1.06 μm and wavelength converted to 0.53 μm. The laser irradiance was varied between 2 × 10 17–10 19 W/cm 2 by varying the laser pulse length, energy and wavelength. The data show that the plastic target was heated above 200 eV to a depth of about 4 μm. The FLY comparisons indicate that the buried layers heated with 0.53 μm light remained near solid density for the duration of the X-ray emission pulse and achieved a peak temperature of 450 ± 50 eV. In the case where the target was heated with 1.06 μm radiation, the density was an order of magnitude lower and the peak temperature achieved was also substantially lower, at 320 ± 50 eV. The depth to which the target was heated was similar at the two wavelengths studied and was not a strong function of irradiance. The aluminium data are presented and compared to radiation-hydrodynamic and spectral modelling.