Abstract
Organic ionic complexes are highly nonlinear optical materials that show considerable promise for frequency conversion and electro-optic modulation applications.1 The organic salt DimethylAminoStilbazolium Tosylate (DAST) has a large second-harmonic-generation (SHG) powder efficiency, roughly 1000 times that of a urea reference standard, by the Kurtz powder technique.2 DAST crystallizes in the monoclinic space group Cc. The anionic tosylate is situated dose to the pyridinium moiety and in effect serves to line up adjacent rows of cationic chromophores in a parallel manner. The only deviation from a completely aligned system is the 20° angle between the long axis of the molecules and the polar a-axis of the crystal. Given the nearly optimal chromophore orientation and the large nonresonant β inferred from the powder SHG test, DAST is expected to have extremely large electro-optic coefficients. Accordingly, single crystals of the Cc phase of DAST were grown from solution. The as-grown crystal habits shown in Fig. 1 indicate the planar orientation of nonlinear chromophoies relative to the largest surfaces of the crystal platelet. The crystals are transparent from 0.7 to 2 μm. As shown in Fig. 2, DAST is biaxial and has a large and highly dispersive refractive index for light polarized approximately parallel to the chromophore axis (i.e., along the polar a-axis). The electro-optic coefficients were measured at 820 nm, by a method previously described by Yoshimura.3
© 1991 Optical Society of America
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