## Abstract

The second-harmonic nonlinear optical susceptibility tensor of $(-)2$-*α*-(methylbenzylamino)-5-nitropyridine single crystals has been calculated from electric-field-induced second-harmonic generation (SHG) data and the oriented-gas model. From this tensor the calculated value of the maximum effective nonlinear optical susceptibility ${d}_{\mathrm{eff}}$ for phase-matched SHG was found to be $6.5\mathrm{pm}{\mathrm{V}}^{-1}.$ Calculations along the whole of the phase-matching locus show that the highest value of ${d}_{\mathrm{eff}}$ is in the region of the lowest values of the second-harmonic wave beam walk-off angle. The walk-off angle of the fundamental is approximately five times smaller. A theory necessary for the optimization of SHG efficiency in biaxial crystals is developed and it is shown that, for the range of crystal lengths and beam walk-off angles available, the criteria for the selection of the parameters ${w}_{0},$
${z}_{0},$ and $\mathrm{\Delta}k$ for optimization of the second-harmonic signal are the same in biaxial and uniaxial crystals. The optimal configuration for the highest second-harmonic efficiency on the phase-matching locus has been determined. The maximum SHG figure of merit, ${P}_{2\omega}(\mathcal{l})/{P}_{\omega}^{2}(0),$ is found to be $3.7\times {10}^{-3}{\mathrm{W}}^{-1}$ for a 50-mm-long crystal.

© 1998 Optical Society of America

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