Second-harmonic generation in biaxial crystals for a focused fundamental Gaussian laser beam: application to ()2-α-(methylbenzylamino)- 5-nitropyridine single crystals

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 deff for phase-matched SHG was found to be 6.5 pm V-1. Calculations along the whole of the phase-matching locus show that the highest value of deff 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 w0,z0, 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, P2ω(l)/Pω2(0), is found to be 3.7×10-3 W-1 for a 50-mm-long crystal.