Kαabsorption spectroscopy: Diagnostic of the radiative preheating of a laser-irradiated layered target

Kα absorption spectroscopy has been used to diagnose the low-temperature, high-density region of layered targets (high-Z on low-Z elements) irradiated by 0.26-μm laser light at irradiances between 2×${10}^{14}$ and 4×${10}^{15}$ W/${\mathrm{cm}}^2$. Time-resolved and time-integrated spectra have been recorded from the front and the rear of the target with high spectral resolution in the 1–3-keV range and low spectral resolution in the 40-eV–4-keV range. Experimental results provide measurements of the electron-temperature gradient shape in the region 50–200 eV. A detailed analysis of the atomic structure of He-like to F-like ions of chlorine and aluminum has been performed to give simulated absorption spectra as a function of plasma parameters. We show here a measurement of the shallow electron-temperature gradient around 100 eV built up by the absorption of x rays emitted by the laser-irradiated high-Z layer. This is in very good agreement with results obtained from a one-dimensional hydrocode including photon transport physics.