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Tungstate crystals are one of the most promising class of Raman materials. In 1969 CaW0 4 and later in 1985 KGd(W0 4 )2 crystal was proposed as a Raman active material [1,2]. This lattice doped with neodymium ions is also well known as a laser active medium [3]. These both features explains why tungstate crystals can be used as amulti functional active element, that is to obtain self-SRS conversion of laser radiation inside the lattice of laser active element.Authors [4] have shown that the important parameters which characterize SRS-active nonlinear material are the values of peak and integral Raman scattering cross sections Zp eak and 2J",. The experiments on spontaneous Raman spectroscopy utilized experimental setup based on the excitation with a cw argon ion laser, working at 488 nm wavelength. The laser intensity at the sample was about 1 W. Raman spectru was recorded by double-spectrometer "Spex-1403" in backwards scattering scheme. The spectral resolution of the system was 0.2+1.0 cm" 1 . The plasma discharge lines of argon laser were cut by an additional pre-monochromator. To compensate the self polarization of spectrometer, a polarization scrambler was placed in front of the entrance slit. The exciting laser intensity and spectrometer slit width had constant values in different sets of measurements, focusing of exciting radiation and collimating of scattered light were the same in all the experiments. Since the Raman scattering was excited by a polarized beam, for some samples we made several experiments with different orientation of the sampl crystallographic axes with respect to the direction of electrical vector E of the exciting beam. Th conditions of the Raman scattering excitation of our measurements were very close to those of Raman lasers with longitudinal pumping.Single crystal as well as polycrystal samples were investigated in our experiments. To compare integral and peak scattering cross sections in different crystals the plane-parallel samples were made from singl crystals with the thickness either 0.7 or 2 mm. Spontaneous Raman spectra of "simple" tungstate crystals with only one type of cations: calcium, strontium, lead and barium were investigated. Each crystal has one very intense Ag line in the spectra which is located at 910 -925 cm" 1 and correspond to the internal symmetrical valent vibration in [W0 4 ] tetrahedron group. Table 1 shows measured data on internal Raman frequency shift and Raman mod linewidth in these crystals together with maximum frequency of external lattice mode at two temperatures.From Table 1 follows that the increase of cation radius and its mass in the row Ca 2+ -> Si -2 " 1 " -» Ba 2+ results in the increase of internal vibronic mode frequency Q R and decrease of its linewidth AQ R . In the First approximation the frequency of i g internal mode of tetragonal group must be determined by interactions inside the tetragonal groups. The sort of cation (Ca 2+ , Sr 2 *, or Ba 2+ ) can influence on this lg frequency only by changing the size of the crystal unit cell an...

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We have measured the resistive transition of molecular beam epitaxy prepared Bi 2 Sr 2 CaCu 2 O 8+x thin films in the presence of perpendicular low magnetic fields H (0 Oe < H < 1100 Oe) for different values of the bias current density J (10 2 A cm −2 < J < 10 5 A cm −2 ). The experimental data show two distinct dissipative behaviours. In the low-current region (J < 10 3 A cm −2 ) the electrical resistivity ρ is independent on J , changing only with H , while in the high-current region (J > 10 4 A cm −2 ) ρ is independent of both the bias current and the magnetic field. The result is considered in terms of thermally activated flux flow-flux creep-steady flux flow crossovers. The role of the statistical distribution of the pinning energy in the vortex dynamics is discussed.

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