We show that the organic salt 4-N,N-dimethylamino-4′-N′-methyl-stilbazolium tosylate (DAST) is a very interesting material for electro-optic applications in the near infrared. The electro-optic coefficients, namely r111, r221, r331, r113, r223, and r333, were determined in the spectral range of 700 up to 1535 nm using optical samples cut from large high quality bulk crystals. DAST combines large electro-optic coefficients, e.g., r111=77±8 pm/V at λ=800 nm and r111=47±8 pm/V at λ=1535 nm, with low dielectric constants, e.g., ε1=5.2±0.4. This combination leads to large polarization-optical coefficients.
A comparison is made between the second-order polarizabilities of nitropyridine derivatives determined with two different methods: electric-field-induced second-harmonic generation (EFISH) and a solvatochromic method. Both techniques yield the same values within the experimental errors, showing that the main contribution of the microscopic nonlinearity arises from a single intramolecular charge-transfer transition. Based on the quantum-mechanical two-level model, the solvatochromic method also yields important molecular parameters, such as transition and excited-state dipole moments. The second-order polarizabilities determined with the EFISH method are shown to follow the theoretical two-level dispersion.
Single crystals of 4-dimethylaminobenzaldehyde-4-nitrophenylhydrazone were grown from solution. We determined their linear-optical (absorption and refractive indices) as well as their nonlinear-optical properties. From the highest nonlinear-optical coefficient d 12 ϭ 270 pm/V at ϭ 1.542 m we determine an effective nonlinear-optical coefficient d eff у 150 pm/V for phase-matched frequency doubling that is, to the best of our knowledge, the largest reported phase-matchable coefficient. The nonlinear-optical properties are discussed in terms of the crystal structure and the molecular hyperpolarizabilities. In addition, the phase-matching configurations for second-harmonic generation and optic parametric oscillation are derived.
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