The photorefractive properties of stoichiometric LiNbO(3) crystals with a small number of defect densities grown by the double-crucible Czochralski method are investigated and compared with the defect densities of commercially available congruent Fe-doped LiNbO(3) crystals. Two-wave-mixing experiments show that novel stoichiometric crystals exhibit larger photorefractive gain and considerably faster response times than congruent ones. The results indicate that the nonstoichiometry defect control of photorefractive crystals is of key importance for the improvement of their properties.
LiNbO 3 single crystals with a composition close to stoichiometry are grown by using a double crucible Czochralski method equipped with an automatic powder supply system. The photorefractive properties are compared with those of LiNbO3 crystals grown from the congruent composition melt. Two beam coupling experiments show that both nondoped and Fe-doped stoichiometric crystals exhibit stronger photorefractive effect than the Fe-doped congruent crystals.
We show that high-temperature reduction in a CO-CO(2) atmosphere increases the photorefractive sensitivity of KNbO(3):Rh at 860nm by 4 orders of magnitude compared with that of the as-grown crystal. The effective trap density is increased by a factor of 3, and the photoconductivity by a factor of 30, and the photorefractive response at a grating spacing of 0.15 mu;m is accelerated by a factor of 400. The grating buildup time at a grating spacing of 0.7 microm and an intensity of 1Wcm(-2) is 0.5 s, a value comparable with that of as-grown KNbO(3):Fe at visible wavelengths. The optical and photorefractive parameters of Rh-doped KNbO(3) subjected to reduction treatment are characterized for wavelengths of 0.48-1.064 microm .
DAST (4-N,N-dimethylamino-4'-N'-methyl stilbazolium tosylate) is an organic salt with one of the highest nonlinear optical susceptibilities and electro-optical coefficients. DAST crystals are therefore seen as good candidates for many photonic applications such as microring resonators
or for THz-devices. The quality of such organic crystal is crucial for any application. We discuss here two different growth methods of single crystalline DAST from solution. Bulk crystals, 1 cm3 in size, and thin crystals, 1 mm2 for a thickness of about 100 ?m are
obtained. The use of a DAST crystal for a microring resonator is also presented
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