Warm photoionized plasmas created by soft-x-ray laser irradiation of solid targets

We report the study of warm plasmas created by soft-x-ray laser irradiation of solid targets in which single-photon photoionization is the dominant energy absorption mechanism. Low-absorption (silicon, Z=14) and high-absorption (chromium, Z=24, and silver, Z=47) targets were heated by ~1 ns duration pulses from a 46.9 nm wavelength soft-x-ray laser. The spectra obtained agree with 1 1/2-dimension simulations in showing that the Si plasmas are significantly colder and less ionized, confirming that in contrast to plasmas created by optical lasers the plasma properties are largely determined by the absorption coefficient of the target material.