Hot surface ionic line emission and cold K-inner shell emission from petawatt-laser-irradiated Cu foil targets

A hot, 2 to 3 keV electron temperature surface plasma was observed in the interaction of a 0.7 ps petawatt laser beam with solid copper-foil targets at intensities > 10(20) W/cm(2). Copper K-shell spectra were measured in the range of 8 to 9 keV using a single-photon-counting x-ray charged-coupled-device camera. In addition to K-alpha and K-beta inner-shell lines, the emission contained the Cu He-alpha and Ly(alpha) lines, allowing the temperature to be inferred. These lines have not been observed previously with ultrafast laser pulses. For intensities less than 3 x 10(18) W/cm(2), only the K-alpha and K-beta inner-shell emissions are detected. Measurements of the absolute K-alpha yield as a function of the laser intensity are in general agreement with a model that includes refluxing and confinement of the suprathermal electrons in the target volume. (c) 2006 American Institute of Physics.