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35LS-P-7
(Cai-xSrx)3(VO4)2 solid solutions - the new crystalline materials for
ultrafast Raman lasers
I. S. Voronina, E. E. Dunaeva, V. V. Voronov, V. E. Shukshin, S. N. Smetanin, L. I. Ivleva
Prokhorov General Physics Institute of the Russian Academy of Sciences, Vavilov str.38, Moscow 119991, Russia edunaeva@lst. gpi.ru
Interest in the search and creation of optical crystals with broad Raman scattering (RS) lines arose due to their high potential for use as active media of stimulated Raman scattering (SRS) lasers with the shortest radiation pulses. Recently, it was shown that it is possible to control the quadratic nonlinear optical activity and ferroelectric properties of a material by changing the structure of composites Caio.5-xPbx(VO4)7 [1, 2] and Ca<,5-i.5*BixCd(VO4)7 [3].
Orthovanadate crystals of the heavy alkali-earth cations (Me = Sr2+, Ba2+, Pb2+) possess the palmierite structure. Interest in use the Sr2+ cation is due to the fact that the properties of Sr2+ (ion size and mass) are closest to those of Ca2+. Usage of Ca3(VO4)2 - Sr3(VO4)2 solid solution with disordered whitlockite structure can provide the formation of the widest homogeneously broadened Raman lines to solve the problem of obtaining SRS radiation pulses shorter than a picosecond.
The (Cai- *Srx)3(VO4)2 (x=0.3; 0.6; 0.9; 1.2; 1.35) crystals were grown by Czochralski method from the platinum crucible in the air in the [100] direction. The starting material was mixed carefully from previously sintered calcium and strontium orthovanadates, Sr3(VO4)2 content in the melt varied from 10 to 45 mol.%. The grown crystals were optically homogeneous, free of cracks and inclusions up to 40 mol.% of Sr3(VO4)2. At 45 mol.% of Sr3(VO4)2 some scattering centers were observed even at low bulk crystallization rate, what indicates the limit of whitlockite phase formation. Ferroelectric domain structure and dislocations density were investigated for the crystals of different composition by the selective chemical etching. The etching patterns indicate that the shape and size of the domains practically don't change with increasing strontium content in the crystal structure. A slight change in the shape of the domains and an increase in their size is characteristic only for solid solutions with a high strontium content. The dislocation density in all the crystals was not higher than 103/mm2. It was estimated that the a and c parameters of the trigonal lattice of the (Cai-xSrx)3(VO4) solid solution increase with increasing the Sr3(VO4)2 content in the composition. The excitation of spontaneous Raman scattering in the samples was carried out at a wavelength of 532 nm (the second harmonic of the YAG:Nd3+ laser).
Data of x-ray diffraction analysis and spontaneous Raman spectroscopy indicate that single-phase crystalline solid solutions with a gradually changing structure are formed in the series (Cai-xSrx)3(VO4)2 with x = 0.3; 0.6; 0.9; 1.2; 1.35.
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