Spectral studies of soft x-ray radiation of laser-produced plasma of various target materials in a wide spectral range.

The work is devoted to experimental study of soft x-ray radiation spectra of laser-produced plasma in a wide spectral range of 5-100Å at the Kamerton facility (GPI) with pulse duration 70 ps, pulse energy 1-5J, and wavelength 0.53 microns at which the laser intensity (power flux density) of 7×10^{14}-3.5×10^{15}W/cm^{2} was achieved. A spectrograph was used, which had transmission diffraction gratings with a ratio of the elementary gap to the period of the structure of 0.25 and 0.41. Detection was performed on both UV-4 x-ray photo film and Fuji TR fluorescent imaging plate. Solid samples from Al, Si, Ti, Cu, Ta, and W were used as targets. The ionization states of the plasma corresponding to various electron temperatures were calculated, which made it possible to estimate the electron temperature by comparison of these calculation results with the experimentally obtained spectra. The estimated electron temperature, which depends on the laser pulse energy and the target material, varied within the range 100-450eV. To verify the correctness of the temperature estimations obtained by such comparison a numerical simulation of plasma radiation was carried out by the use of prismspect computer program. It was found that the results of this simulation are in good agreement with estimations on the base of experimentally obtained spectra. The analysis of these spectra showed that tantalum, tungsten, or titanium targets are the best candidates among the tested ones for the use of laser-produced plasma as a radiation source in the "water window" spectral range (23-44Å) for applications in biology and medicine.

Mode-locking optimization with a real-time feedback system in a Nd:yttrium lithium fluoride laser cavity.

We present a control system, which allows an automatic optimization of the pulse train stability in a mode-locked laser cavity. In order to obtain real-time corrections, we chose a closed loop approach. The control variable is the cavity length, mechanically adjusted by gear system acting on the rear cavity mirror, and the controlled variable is the envelope modulation of the mode-locked pulse train. Such automatic control system maintains the amplitude of the mode-locking pulse train stable within a few percent rms during the working time of the laser. Full implementation of the system on an Nd:yttrium lithium fluoride actively mode-locked laser is presented.

Hugoniot data of plastic foams obtained from laser-driven shocks.

In this paper we present Hugoniot data for plastic foams obtained with laser-driven shocks. Relative equation-of-state data for foams were obtained using Al as a reference material. The diagnostics consisted in the detection of shock breakout from double layer Al/foam targets. The foams [poly(4-methyl-1-pentene) with density 130 > rho > 60 mg/cm3] were produced at the Institute of Laser Engineering of Osaka University. The experiment was performed using the Prague PALS iodine laser working at 0.44 microm wavelength and irradiances up to a few 10(14) W/cm2. Pressures as high as 3.6 Mbar (previously unreached for such low-density materials) where generated in the foams. Samples with four different values of initial density were used, in order to explore a wider region of the phase diagram. Shock acceleration when the shock crosses the Al/foam interface was also measured.