Victor V. Prokofiev

Growth of single-crystal photorefractive fibers of Bi12SiO20 and Bi12TiO20 by the laser-heated pedestal growth method

Abstract Photorefractive single-crystal fibers of Bi 12 SiO 20 up to 90 mm in length and Bi 12 TiO 20 up to 50 mm in length with diameters of 650–1200 μm were grown by the laser-heated pedestal growth (LHPG) method. Both Bi 12 SiO 20 and Bi 12 TiO 20 fibers were pulled from stoichiometric (6:1) melts at pulling rates of 0.3 and 0.2 mm/min, respectively, the feeding rate was 0.1 mm/min. Growth conditions, morphology and chemical composition of the grown fibers were studied. The possible mechanisms of crystallization of incongruently melting Bi 12 TiO 20 fiber from the stoichiometric melt were discussed. The energy-exchange effect was observed in the BSO fibers at the wavelength λ = 0.5145 μm .

Nonlinear self‐channeling of a laser beam at the surface of a photorefractive fiber

We experimentally observed the self‐channeling of the light beam in photorefractive Bi12TiO20 fiberlike sample owing to the strong fanning effect. It results in significant speed up of the photorefractive response time in waveguides and in anomalous dependence of the response time on the applied ac electric field amplitude: the higher electric field, the faster response.

Combined formation of a self-pumped phase-conjugate mirror and spatial subharmonics in photorefractive sillenites

We found that the formation of self-pumped phase-conjugate mirrors (SPPCM) in photorefractive Bi12TiO20 crystals under external alternating electric field is accompanied by strong enhancement of spatial subharmonics. This combined formation of the fundamental grating and its spatial subharmonics results in an expansion of the spatial-frequency band allowed for SPPCM recording.

Light-induced absorption in a Bi12TiO20 crystal

Evolution of the light-induced absorption in a Bi12TiO20 crystal is investigated at a wavelength of 633 nm. It is found that the absorption coefficient evolution consists of fast and slow components with different characteristic response time. The light absorption coefficient decreases from 0.9 to 0.16 cm-1 after keeping the sample in darkness for six months. We propose a new charge-transport model that includes the deep donors in three valence states and the shallow traps. It is shown that the theory developed provides an explanation for the observed features of the increase and dark decay of the light-induced absorption. The material parameters of the Bi12TiO20 crystal are estimated from the best fit of the theoretical model with the experimental data.

Fast adaptive interferometer with a photorefractive GaP crystal

The performance of an adaptive interferometer based on mixing of light waves with different polarization states in a photorefractive GaP crystal at lambda=0.633mum is described. Both high sensitivity and fast response time are achieved with a low-power He-Ne laser. The parameters of the interferometer are appropriate for remote ultrasound detection in an industrial environment.

Beam fanning and double phase conjugation in a fiber-like photorefractive sample

Unexpectedly fast response (35 ms) of beam fanning has been measured in a fiber-like photorefractive sample of Bi/sub 12/TiO/sub 20/ (BTO) crystal. Nonlinear interaction between different directions of fanned beams is responsible for unusual angular distribution of the fanning emerged from the fiber that can be used for double phase-conjugate mirror (DPCM) recording with higher efficiency in a wider range of the pumps incidence than in a bulk sample. The DPCM with conversion efficiency up to 8% has been recorded in the BTO fiber at /spl lambda/=632.8 nm for a 2/spl times/3 mW input light power. Practically, it means that no adjustment is needed to achieve an effective interaction of mutually incoherent beams, except introducing the pump beam into the fiber. >

Double phase conjugation in Bi12TiO20 photorefractive fiber-like crystal

Abstract An experimental investigation of phase conjugation of two mutually incoherent laser beams in the photorefractive Bi 12 TiO 20 fiber is presented. Phase conjugate wave reflectivity close to 7% and with a response time of a few seconds was obtained at λ = 632.8 nm with a 24 mW power HeNe laser under an alternating external electric field.

Fast photorefractive response in B(12)SiO(20) in the near infrared.

The polarization self-modulation effect was applied for effective measurement of the characteristic response time of nominally pure Bi(12)SiO(20) (BSO) at wavelengths of 810 and 980 nm. Owing to oxygen deficiency in the crystal lattice, the BSO crystals showed unusual photorefractive sensitivity and remarkable operation speed in the near-infrared spectral region. A response time of 130 ms was measured at 810 nm, and a response time of 540 ms was measured at 980 nm, with incident intensities of 110 and 200mW/cm(2), respectively. To our knowledge, this is the first experimental evidence of a subsecond response in the infrared for a nonsemiconductor photorefractive material.

Fast mutually pumped phase conjugation using transient photorefractive coupling

Unusually fast mutually pumped phase-conjugation (MPPC) is achieved in a Bi12TiO20 crystal by using transient photorefractive beam coupling under a dc electric field. Pulses of phase-conjugate waves with a buildup time of 4.5 ms and a width of 50 ms at an input intensity of 2×0.8 W/cm2 are obtained after applying a rising front of external electric field to the crystal. A phase-conjugation efficiency as high as 25% of the incident light power is measured.

Holographic recording of complex images by double phase conjugation in Bi(12)TiO(20) fiberlike crystal.

Volume holographic recording of complex images with a double phase-conjugation mirror in a fiberlike Bi(12)TiO(20) single crystal, mutually pumped by two separate He-Ne lasers, is experimentally demonstrated. Complex images can be stored and reconstructed by use of even a partial input image. The advantages of the small-cross-section, light-confining photorefractive sample in comparison with bulk crystal are a wider spatial bandwidth of recorded images and the possibility of recording holograms by application of smaller ac voltages.