Combined interferometric-mask method for creation of micro- and sub-micrometric scale 3D structures in photorefractive materials

A new combined interferometric-mask method is suggested and realized for creation of 3-dimensional (3D) holographic periodic and quasi-periodic structures in photorefractive materials. The method is based on the preparation of 2-dimensional (2D) micrometric scale masks with different symmetries and illumination of the photorefractive material through the mask by Gaussian beam in combination with back reflecting mirror. The counter-propagating beam geometry builds up Gaussian standing wave, which determines the third half-wave period of the grating in the axial direction. Thus, the created 3D intensity pattern can be represented as numerous mask-generated 2D quasi-periodic structures located in each anti-node of the standing wave. The formed intensity pattern can be imparted into the photorefractive medium via electro-optic effect, thus creating micro-and sub-micro scale 3D refractive index volume gratings with new symmetries and properties. The gratings were recorded by 532 nm cw laser beams in Fe-doped lithium niobate crystals taking into account their high photorefractive properties and possibility of creating the persistent gratings. The gratings formed have similar to 10 mu m period in radial and azimuthal directions and 266 nm in axial direction. The gratings were interrogated by diffraction of low intensity Gaussian probe beams from the recorded structures.