REFLECTIVITY OF LASER-PRODUCED PLASMAS GENERATED BY A HIGH-INTENSITY ULTRASHORT-PULSE

Solid state density aluminum and carbon plasmas were generated by 350 fs KrF laser pulses at intensities of 10(17) W cm-2. Reflectivity, x-r ay emission, and spectra of the backscattered radiation were measured as a function of the laser polarization, angle of incidence, and inten sity (I). For p-polarized light, the absorption (A) is almost intensit y independent for 10(15) W cm-2<I<2x10(17) W cm-2, and can reach value s up to A = 0.8. For constant laser intensity, p-polarized light is up to a factor of 15 more efficient in generating x rays than s-polarize d light. A polarization and angle of incidence-dependent absorption me chanism, such as resonance absorption or vacuum heating, is consequent ly important. The spectral line shape and positions of the reflected r adiation from the carbon plasma showed a substantial intensity depende nce. It is demonstrated that the backscattered spectrum is influenced by the plasma expansion (Doppler effect) and the temporal development of the electron density.