Bessel standing wave technique for optical induction of complex refractive lattice structures in photorefractive materials

摘要

A novel counter-propagating Bessel beam technique is suggested and realized for optical formation of complex two-dimensional (2D) refractive lattice structures in photorefractive materials. The 2D complex lattices optically induced by the suggested method are a combination of annular and planar gratings with refractive index modulation in the radial direction in the transverse plane and the in axial direction along the optical beam propagation. The recording of the lattices is performed by 532 nm and 633 nm laser beams. The counter-propagating beam geometry builds up the Bessel standing wave with periodic annular structure in each anti-node. The refractive lattices are recorded in Z- and Y-cut 2 mm thick photorefractive lithium niobate crystals singly doped by Fe and doubly doped by Fe and Cu. The readout of recorded lattices is performed by Gaussian red and green probe laser beams. The direct observation of recorded lattices by optical phase microscope is also performed. The formed photonic structures have a period of 10 ± 1 m in the radial direction and a half-wavelength standing wave period of 266 nm or 316.5 nm in the axial direction. The diffraction efficiency of the photonic lattices reaches up to 25%.