No abstract

A novel spectrograph comprised of a transmission grating, toroidal mirror, and microchannel plate detector is presented here. It is capable of detecting spectra in the wavelength range from 5 to 150 Å with a resolution of about 1.5 Å. Owing it to high efficiency, even an x-ray spectrum of a low-energy laser produced plasma, i.e., emission of the order of 10−10 J/sr, can be measured in a single shot.

Solid state density aluminum and carbon plasmas were generated by 350 fs KrF laser pulses at intensities of 1017 W cm−2. Reflectivity, x-ray emission, and spectra of the backscattered radiation were measured as a function of the laser polarization, angle of incidence, and intensity (I). For p-polarized light, the absorption (A) is almost intensity independent for 1015 W cm−2<I<2×1017 W cm−2, and can reach values 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-polarized light. A polarization and angle of incidence-dependent absorption mechanism, such as resonance absorption or vacuum heating, is consequently important. The spectral line shape and positions of the reflected radiation from the carbon plasma showed a substantial intensity dependence. It is demonstrated that the backscattered spectrum is influenced by the plasma expansion (Doppler effect) and the temporal development of the electron density.

The interaction of subpicosecond KrF-laser pulses with polished and colloidal metal surfaces at an intensity of 8×1015 W/cm2 was investigated experimentally. The measurements with spectral and temporal resolution for the colloidal targets showed a higher energy conversion efficiency into soft x rays and an increase in x-ray pulse lengths.