Optical induction of 3D refractive lattices in doubly doped LiNbO$_{3}$ photorefractive crystal

The optical induction of 3D rotational symmetry refractive lattices in doubly doped photorefractive and photochromic LiNbO$_{3}$:Fe:Cu crystal by combined interferometric-mask method was performed. The method is based on the spatial light modulation by amplitude mask in the transverse plane and the use of counter-propagating beam geometry building up a Gaussian standing wave, which defines the light intensity modulation in the axial direction with half-wavelength periodicity. Masks with rotationally symmetrical structures are used in the experiment. The created intensity pattern was imparted into the LiNbO$_{3}$:Fe:Cu crystal thus creating refractive lattice with the periods of 20 – 60 $\mu$m in the radial and azimuthal directions and 266 nm in the axial direction. The refractive and dispersive properties of the recorded lattices were studied.