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[en] Complete text of publication follows. We report about experiments on study of wavefront of laser beam 130 mm in aperture by a radial-shear interferometer. Following wavefronts were put to the test: the wavefront of chirped pulse of 500 ps in duration at the output of amplifying channel (at the input of laser pulse compressor), and the wavefront of 0.7 to 0.8 ps pulse at the output of the compressor, after propagation through air and a window of the vacuum chamber to the parabolic mirror. Energies of these pulses at a nominal pumping mode of the amplifying channel were correspondingly 12 to 15 J and 10 to 12 J. Comparative measurements of the static aberrations of wavefront, and dynamic aberrations arising at a pumping of the amplifying channel, at a nominal and small pulse energy at the input of the channel have been performed. Last mode has been realized for elimination of non-linear phase deformations of the wavefront for the purpose of separated studying of thermooptical aberrations. Wavefront defocus at the input of the compressor leads to magnification of pulse duration at targets and deterioration of focusing of radiation, and achievement of the maximum radiant intensity becomes impossible. Taking into account the measured aberrations of the wavefront at the input and output of the compressor compensation of dynamic defocus of the wavefront has been performed, the defocus and astigmatism of the wavefront at the output of the compressor thereby have been eliminated and pulse duration 0.7 to 0.8 ps in focus of the parabolic mirror is obtained. Moreover, the account of aberrations has allowed to raise accuracy of positioning of a target, the minimal a focal spot diameter of 5 to 6 microns FWHM with the content of energy 20 to 30 % within this diameter has been thus obtained. Small diameter of a focal spot is provided thanks to rather high temporary contrast of a laser pulse amounting 1011 on intensity. Thus, as a result of application of the featured method the intensity of laser radiation on a target I ∼ (1 to 2) x 1019 W/cm-2 is reached.
[en] Complete text of publication follows. Energy of the laser pulse interacting with solid and gas targets partially transmits to fast electrons, which in turn slowing-down in target, create a continuous and characteristic radiation. Investigation of this radiation is important for studying the processes of generation and transport of fast electrons in target material. On 20 TW picoseconds laser facility SOKOL-P, the research of copper targets continuous X-ray spectrum was conducted in the range of photon energies of 0.6-3000 keV and yield of Cu-Kα characteristic line was measured. A spectrograph with flat crystal (LiF d = 2.15 A) was used to measure the Kα-radiation of copper. Registration of the spectrum was carried out on a CCD camera. Front-side measurements were performed for targets of 35 and 50 μm thickness. Yield of Cu-Kα practically does not depend on the intensity of laser radiation in the range of three orders. Measurements from the back side were conducted for targets of 35 μm thickness. They show a monotonic increase of the line yield depending on the intensity with saturation at about 1018 W/cm2. Measurement of laser-plasma continuous spectrum in the energy range 0.6-4.5 keV was carried out using X-ray spectrometer based on spherical mirrors of total external reflection. In combination with X-ray mirrors, the filters that allow registration the radiation in five narrow energy regions were used. The spectral distribution of soft X-rays in the energy range 0.6-4.5 keV is characterized by the effective electron temperature of ∼ 0.5 keV. The hard X-rays spectra measurement in the energy range 25-90 keV was carried out at the front of a target by K-filter method using spectrometer with semiconductor detectors DDR 08/0.5. The X-rays with energies above 100 keV were detected using gray lead filters method by three-channel spectrometer based on photoelectronic multiplier FEU-60 with CsJ (TI) scintillators. Spectral distribution of X-rays (ε> 100 keV) is characterized by effective temperature of electrons in the hundreds of keV diapason, changing the value of Teff from 200 keV at 1 = 3 x 1017 W/cm2 to 600 keV at I ∼ 1019 W/cm2. In 20-100 keV range of quanta energy the X-ray spectra have a nonmonotonic character with maximum value at about 5 x 1011 keV / keV at energy of 50-60 keV.