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 <i>d</i><sub>eff</sub> for phase-matched SHG was found to be 6.5 pm V<sup>−1</sup>. Calculations along the whole of the phase-matching locus show that the highest value of <i>d</i><sub>eff</sub> 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<sub>0</sub>, z<sub>0</sub>, and Δk 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, <i>P</i><sub>2ω</sub>(<i>l</i>)/<i>P</i><sub>ω</sub><sup>2</sup>(0), is found to be 3.7 10<sup>−3</sup> W<sup>−1</sup> for a 50-mm-long crystal.
© 1998 Optical Society of America
P. Kerkoc, R. T. Bailey, F. R. Cruickshank, and D. Pugh, "Second-harmonic generation in biaxial crystals for a focused fundamental Gaussian laser beam: application to ()2-α-(methylbenzylamino)- 5-nitropyridine single crystals," J. Opt. Soc. Am. B 15, 438-445 (1998)