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 a largely determined by the absorption coefficient of the target material.