X‐ray spectra from high‐intensity subpicosecond laser produced plasmas

The interaction of high‐intensity subpicosecond KrF*‐laser pulses with aluminum plasmas has been investigated. The laser pulse absorption and the x‐ray production have been related at a series of intensities up to 1017 W/cm2 and different angles of incidence. Soft x‐ray spectra were measured in the wavelength range from 7 to 150 Å with various spectrographs. The spectra show distinct dependences on the laser intensity, the polarization, and the angle of incidence. The observed dependence of the spectra on the intensity and on the angle of incidence is the result of both the angular dependence of the laser pulse absorption and that of the conversion efficiency of the absorbed energy into soft x‐ray emission. The spectra are influenced by the size of the absorption volume, the electron density where the absorption mainly takes place, and other parameters, such as the electron temperature.