Thermooptic investigation of impurity centers in Cu-doped Bi12SiO20 crystals

Temperature dependences of the optical absorption of BSO:Cu crystals were investigated at photon energies between 1.36 and 3.46 eV and temperatures between 85 and 700 K. These dependences are analyzed for the energy model of a partially compensated p-type semiconductor taking into account the temperature dependence of the concentration of shallow and deep ionized acceptors. Fiz. Tverd. Tela (St. Petersburg) 40, 1246–1251 (July 1998)     

Dielectric relaxation in Bi12SiO20 crystals

Anomalies of the dielectric properties of undoped and aluminum-and gallium-doped crystals of Bi₁₂SiO₂₀ are investigated in the frequency and temperature range ν=10²–10⁸ Hz and T=300–800 K. They are shown to be due to Debye relaxation processes and determined by the relaxor parameters. The mechanism of electron thermal polarization is discussed. Fiz. Tverd. Tela (St. Petersburg) 39, 1223–1229 (July 1997)     

Thermal ionization of impurity centers in Fe-doped Bi12SiO20 and Bi12GeO20 crystals

The spectral and temperature dependence of the optical absorption and thermally stimulated depolarization currents in Fe-doped Bi₁₂SiO₂₀ and Bi₁₂GeO₂₀ crystals are investigated in the photon energy range 1.36–3.46 eV and temperature 85–750 K. The results show thermally induced electron redistribution between donor and acceptor levels and defect association-dissociation processes and are discussed using the configuration-coordinate model. Fiz. Tverd. Tela (St. Petersburg) 41, 1006–1011 (June 1999)     

Dielectric relaxation in Bi12SiO20: Cr crystals

A study is reported of the temperature and frequency dependences of the permittivity and losses in Cr-doped Bi₁₂SiO₂₀ crystals at sonic frequencies and in the range 300–800 K. A number of dielectric anomalies and a close-to-linear Cole-Cole diagram have been observed. The results are discussed by invoking the concepts of electron hopping and screening of the induced polarization through the relaxation of local lattice distortions.     

Thermal defect formation in undoped and Cr-and Mn-doped Bi12SiO20 crystals

The thermally stimulated depolarization currents and the temperature dependences of optical absorption are investigated. Interaction processes between defects are observed. A model consisting of association-dissociation of quasidipoles in the form of donor-acceptor pairs with a distribution of activation energies and relaxation times is proposed. Fiz. Tverd. Tela (St. Petersburg) 41, 1593–1596 (September 1999)     

Diffraction efficiency and energy transfer in two-wave mixing experiments with Bi12SiO20 crystals

The diffraction efficiency and energy transfer are investigated in photorefractive Bi₁₂SiO₂₀ crystals (BSO). Dependence on fringe spacing, electric fields, light intensity and rise-time constants are reported. The optimum crystallographic orientation for each effect is determined for vertical polarization of the recording beams. It is shown that beam coupling is a very sensitive phenomenon in BSO crystals where charge transport lengths are equivalent to usual fringe spacings. Experimental results are interpreted on the basis of the nonlinear theory of self-diffraction developed by Kukhtarev et al. [10].     

The polarizing effect in Bi12GeO20 crystals

The results of the measurement of the d-c electric field effect on the resonant frequency of the longitudinally vibrated bars from Bi₁₂GeO₂₀ crystals parallel to the planes (001) and (111) are given. The polarizing correction terms of the elastic couplings are calculated from the change of the frequency.     

Extraction of Self-Diffraction Wave in Photorefractive Bi12SiO20 Crystals

When two waves are coupled in Bi₁₂SiO₂₀ crystals, the polarization states of the signal wave are affected by the self-diffraction. We have theoretically studied the influence of the self-diffraction on the polarization of the signal wave. The change of polarization states are strongly affected by the self-diffraction effect when the external field is applied. We present a new method that converts the change of polarization into an intensity signal.     

Anisotropic properties of volume holograms in Bi12SiO20 monocrystals

A theoretical and experimental study is made on light diffraction from holographic diffraction gratings, recorded in cubic photorefractive crystals Bi₁₂SiO₂₀ with (110) cut, for two orientation of the grating wave vector,K [001] andK [110], when an external electric field is applied.     

Quasipermanent hole-photorefractive and photochromic effects in Bi12TiO20 crystals

We report the presence of quasipermanent effects of photochromic and hole-photorefractive nature in Bi₁₂TiO₂₀ (BTO) at low irradiance at 514.5 nm. A new selective two-wave mixing (S2WM) detection technique was used that allows to separately detect phase and amplitude gratings. S2WM is used in this work for operating a self-stabilized recording setup which allows to produce unusually large quasipermanent effects. We also show that stabilized recording is necessary to obtain reliable information from hologram erasure experiments. Results reported in this paper show the complex nature of recording in BTO and the capabilities of stabilized recording and S2WM for fundamental and applied research on photorefractive crystals.     

Nanosecond light energy transfer in Bi12SiO20 AT 532 nm

We demonstrate for the first time to our knowledge the possibility of two beam coupling in photorefractive crystals of BSO under nanosecond excitation. We report the experimental measurements of the gains we have obtained. We explain it by solving the set of equations given by Kukhtarev in a particular case.     

Electron paramagnetic resonance studies of photorefractive crystals II: Fe3+ doped Bi12SiO20 with copper vapour laser illumination in 10–100 K range

Photo-induced charge transfer and its kinetics were investigated in Bi₁₂SiO₂₀ in 10–300 K temperature range, using EPR of Fe³⁺ centre, underin situ illumination with copper vapour laser (CVL). The decay kinetics was found to follow double exponential behaviour. Relaxation of the photo-induced electron transfer to the preillumination condition occurred even at 10 K. Shallow traps were, therefore, associated with the electron trapping, leading to a better understanding of the fast photorefractive response of BSO.     

Drift mobility of photogenerated current carriers in Bi12GeO20 crystals

The drift mobility of photogenerated electrons and holes in Bi₁₂GeO₂₀ crystals with different degrees of doping is investigated experimentally. Fiz. Tverd. Tela (St. Petersburg) 40, 2054–2055 (November 1998)     

Growth and characterization of Nd:Bi12SiO20 single crystal

A Nd:Bi₁₂SiO₂₀ crystal was grown by the Czochralski method. The thermal properties of the crystal were systematically studied. The thermal expansion coefficient was measured to be α=11.42×10^?6 K^?1 over the temperature range of 295–775 K, and the specific heat and thermal diffusion coefficient were measured to be 0.243 Jg^?1 k^?1 and 0.584 mm²/s, respectively at 302 K. The density was measured to be 9.361 g/cm³ by the buoyancy method. The thermal conductivity of Nd:Bi₁₂SiO₂₀ was calculated to be 1.328 Wm^?1 K^?1 at room temperature (302 K). The refractive index of Nd:Bi₁₂SiO₂₀ was measured at room temperature at eight different wavelengths. The absorption and emission spectra were also measured at room temperature. Continuous-wave (CW) laser output of a Nd:Bi₁₂SiO₂₀ crystal pumped by a laser diode (LD) at 1071.5 nm was achieved with an output power of 65 mW. To our knowledge, this is the first time LD pumped laser output in this crystal has been obtained. These results show that Nd:Bi₁₂SiO₂₀ can serve as a laser crystal.     

Fringe formation theory for real-time holographic interferometry using Bi12SiO20

A simple theory has been developed to explain the fringe formation in real-time holographic interferometry using BSO (bismuthsiliconoxide) crystal for interferometric applications. Detailed analysis has been given to choose the optimum size of the crystals.     

Increase the size of Bi12SiO20 real-time hologram for three-dimensional display

A large-screen, real-time hologram device using Bi₁₂SiO₂₀ (BSO), which enables observation of reconstructed images by parallax vision has been fabricated. The BSO wafer size of the device was 70x70x3 mm³. The wafer was dipped in silicon oil to avoid the electric discharge between the electrodes. The conditions were studied to obtain complete reconstruction from the large Fresnel volume-type real-time hologram and a uniform diffraction efficiency was obtained over the entire area including the core of the crystal. Irradiation at a level of 4 mJ/cm² yielded a diffraction efficiency of 0.5%. Binary and half-tone images were holographically recorded and reconstructed. The reconstructed images could be observed by the naked eye, including the actual depths.     

Degenerate four-wave mixing in photorefractive Bi12GeO20 crystals involving internal reflections

Degenerate four-wave mixing in photorefractive Bi₁₂GeO₂₀ crystals involving internal reflections is studied theoretically and experimentally. Two sets of four-wave mixing exist simultaneously. One set is at the Bragg angle while the other is off the Bragg angle. Theoretical and experimental relations between the wavefront reflectivity and the external incident angle of the reading beam, as well as the reference-to-object beam ratio, are investigated.     

Spectral dependence of cross-talk between photorefractive gratings in Bi12SiO20 in diffusion regime

12 SiO₂₀ crystals in the diffusion regime. We find unusually high cross-talk for two gratings with close spatial frequencies at wavelengths 488 and 476 nm. The results indicate that the density of free charge carriers does not directly follow light modulation at low spatial frequencies. Received: 2 December 1996/Revised version: 20 February 1997