Peculiarities of second harmonic generation by paraxial beams with radial / azimuthal polarization in type II nonlinear crystal

In this work we investigate the light patterns generated by paraxial radial and azimuthal polarization beams in type-II nonlinear crystal. We show that in paraxial case the second harmonic intensity pattern generated by the radial / azimuthal polarization beams can be expressed similarly to the Hermite-Gaussian HG(11) mode. In addition, numerical simulations were carried out taking into account diffraction, walk-off, and pump depletion. The numerical simulations have shown that even with pump depletion the resulting second harmonic beam consists of 4 maxima. Also, experimental results are presented, which confirm theoretical predictions. Interference patterns indicate phase shifts of pi between neighbouring maxima.