Spatiotemporal light bullets and supercontinuum generation in beta-BBO crystal with competing quadratic and cubic nonlinearities

摘要

We experimentally study filamentation and supercontinuum generation in a birefringent medium [beta-barium borate (beta-BBO) crystal] pumped by intense 90 fs, 1.8 mu m laser pulses whose carrier wavelength falls in the range of anomalous group velocity dispersion of the crystal. We demonstrate that the competition between the intrinsic cubic and cascaded-quadratic nonlinearities may serve as a useful tool for controlling the self-action effects via phase matching condition. In particular, we found that spectral superbroadening of the ordinary polarization is linked to three-dimensional self-focusing and formation of self-compressed spatiotemporal light bullets that could be accessed within a certain range of either positive or negative phase mismatch. In the extraordinary polarization, we detect giant spectral shifts of the second harmonic radiation, which are attributed to a light bullet-induced self-phase matching. (C) 2016 Optical Society of America