Applied Crystallography

Biography

Biography: Rocio Jauregui

Abstract

An alternative to diffraction techniques is the characterization of the point symmetry group of a crystal by its effects on the nonlinear optical response encoded in the susceptibility tensors. In this work, we show that it is possible to perform complementary symmetry studies of nonlinear materials by using nonlinear processes besides second harmonic generation ¹. We also show that structured light can enhance the tracks of the symmetry of a crystal on its nonlinear optical properties^2,3 . We focus on the usage of light beams that can be described as the superposition of plane waves with wave vectors confined in a cone and with cylindrical symmetry on the angular spectrum (Bessel beams).  This is equivalent to observing the crystal simultaneously from many different angles. The polarization structure of these beams out of the paraxial regime allows to incorporate information from all the components of the susceptibility tensors using a single structured illumination beam. The crystallographic analysis is exemplified for the parametric down conversion process⁴ . It is shown that, for an uniaxial birefringent nonlinear crystals, a proper orientation of a non paraxial Bessel beam induces the emission of photon pairs in directions that reflect directly the point symmetry. Both the flux rate of signal photons (with a clear classical analog) and coincidence detections (with a pure quantum interpretation) exhibit traces of the crystal symmetries.