[en] The birefringence of (Ca_0.28Ba_0.72)_0.75(Sr_0.60Ba_0.40)Nb₂O₆ crystal is measured basing on polarization- extinction method and conoscopic interference method. Experimental results show that the birefringence in this crystal is up to 10^-5, the natural birefringence in this crystal is (n_o-n_e)=5.89 x 10^-5 with the He-Ne laser wavelength at 632.8 nm and the birefringence grads with wavelength at 532 nm is 5.68 x 10^-5, which indicate the good optical homogeneity of this crystal. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

[en] In open-circuit boundary conditions, tetragonal tungsten bronze (CSBN75) crystals are settled on one of arms of Michelson's interferometer in such a way that even minor perturbation of the penetrated beam can be enlarged and observed through the Michelson's interferometer rings. The experimental results shows that CSBN75 (Δn < 0) are self-defocusing photorefractive crystals. In this paper, qualitative and quantitative discussion on the light-induced change in the index of refraction is given. The self-defocusing character in CSBN75 suggests that it is possible to observe the dark spatial solitons with this crystal in further investigation. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

[en] Conoscopic interference of polarized light for the white-light and LPS-7,5Volts direct current semiconductor laser (Green light) with wavelength at 532 nm in (Ca_0.28Ba_0.72)_x(Sr_0.60Ba_0.40)_1-xNb₂O₆ crystals were observed with the beams transmitting along optical-axes and deflection optical-axes from 0 to 140 . Endo-exo variation from looseness to tightness of conoscopic interference patterns were analyzed in theory. A hyperbolic black cross of interference patterns were observed as well as its formation process was proposed in this paper. Also, the inferences of the birefringence with different Ca²⁺-doped were obtained in this investigation. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)