Bi12SiO20 Crystals Research Articles

Electrical conductivity of Bi12SiO20 single crystals doped with Os, Re, Ru, and Rh

Bi12 SiO20 crystals doped with Os, Re, Ru, and Rh were grown by the Czochralski technique, and their conductivity (real and imaginary parts) was measured as a function of temperature and frequency. The results are interpreted as evidence that the charge transport in the crystals is due to hopping along chains of localized states.

Transition between superluminal and subluminal light propagation in photorefractive Bi12SiO20 crystals

We demonstrated superluminal light propagation with a negative group velocity of -5.7 m/s in a photorefractive Bi 12SiO20 crystal by using the dispersive phase coupling effect in a nondegenerate two-wave mixing process. To the best of our knowledge, this is the first experimental demonstration of superluminal light propagation at room temperature in solids by using a classical wave mixing technique. In addition, we showed the tunability of the group velocity of light between the negative (superluminal light) and the positive (subluminal light) by simply tuning the experimental conditions such as the frequency of the coupling beam, the incident intensity, and the externally applied electric fields.

Measurement of the spatiotemporal surface charge distribution in an ac plasma display cell using Pockels effect

We measured the surface charge distribution in a coplanar type alternating current plasma display panel cell by the longitudinal electro-optic amplitude modulation method with BSO (Bi12SiO20) single crystal. The effects of the initialization condition were investigated to take care of the errors coming from the charge relaxation phenomena of the BSO crystal. Using BSO single crystal as the dielectric layer, the two-dimensional spatiotemporal surface charge distribution was successfully measured in a discharge cell with a discharge gas of neon and xenon 4% at the pressure of 100torr driven by square-type sustaining pulses. The temporal behavior of the surface charge is compared with the simulated result and the measurement of the infrared light emission from the discharge. The positive and negative surface charges show somewhat different spatiotemporal characteristics.

A method for determining the charge state of chromium in Cr-doped Bi12SiO20 and Bi12TiO20 materials

A chemical method for determination of the charge state of chromium in B2O3-based materials (Bi12SiO20 and Bi12TiO20 single crystals) in a wide Cr concentration range (1 × 10−5 − 2 × 10−2 wt.%)is proposed. The method is based on a color reaction between Cr6+ and diphenylcarbazide in an acid medium.

Phase-Coupling-Induced Ultraslow Light Propagation in Solids at Room Temperature

We show that the group velocities of light pulses can be decelerated dramatically by the use of a dispersive phase-coupling effect through a wave mixing process. We have observed experimentally such a phase-coupling-induced ultraslow light propagation with a group velocity as low as 0.05 m/s in a photorefractive Bi12SiO20 crystal at room temperature. Moreover, the ultraslow light is amplified in the Bi12SiO20 crystal because of the unidirectional energy transfer from a coupling beam to the ultraslow light. This technique to produce ultraslow light propagation is valid for all nonlinear wave mixing processes with a dispersive phase-coupling effect.

Interaction of running gratings of the space charge and conductivity in photorefractive Bi12Si(Ti)O20 crystals

The simultaneous excitation and nonlinear interaction of the space-charge and photoconductivity gratings are studied experimentally in photorefractive Bi12SiO20 and Bi12TiO20. The measurements are performed using the diffraction technique, which implies the illumination of the crystal by an oscillating interference pattern (λr=532 nm) along with the application of dc and ac electric fields and detection of the diffracted probe beam (λp=650 nm). Such illumination excites the running photoconductivity grating, which interacts with the ac component of the applied field giving rise to the space-charge wave. Being the eigenmode of the space-charge oscillations, this wave reveals itself as a low-frequency resonant maximum at the frequency-transfer function of the detected signal. The drift mobilities of electrons are estimated using the developed technique: μ=(1.1–1.4) ×10-2 cm2/V s (Bi12SiO20, T=296–298 K) and μ=2.8×10-3 cm2/V s (Bi12TiO20, T=293 K).

Nonlinear interaction of moving space-charge and photoconductivity gratings in Bi12SiO20 crystal

A nonlinear interaction of moving space-charge and photoconductivity gratings is experimentally investigated. In the presence of a dc electric field, a crystal is irradiated with an oscillating interference pattern with a spatial frequency K and an oscillation frequency ω. An ac electric field with a frequency \gM is also applied to the sample. At certain frequencies ω and \gM, the crystal exhibits two types of interacting oscillations: the space-charge grating moving with velocity |ω−Ω|/K and the photoconductivity grating moving with velocity −ω/K. The effect is studied using the method of the nonstationary photoelectromotive force in a photorefractive Bi12SiO20 crystal.

Effect of higher order nonlinear optical processes on optical absorption in the photorefractive BSO and BGO crystals

The processes of nonlinear refraction and nonlinear absorption are studied in the photorefractive Bi12SiO20 (BSO) and Bi12GeO20 (BGO) crystals at a wavelength of a picosecond Nd:YAG laser of 1064 nm. The nonlinear refraction in the crystals is shown to be related to the Kerr effect, and the nonlinear absorption at this wavelength, to three-photon absorption. The three-photon absorption coefficients of the BSO and BGO crystals are equal, respectively, to (2.5±0.8) ×10−20 and (4.4±1.3) ×10−20 cm3W−2.

Nonlinear Optical Characteristics of BSO and BGO Photorefractive Crystals in Visible and Infrared Ranges

Nonlinear refraction, nonlinear absorption and optical limiting in photorefractive crystals Bi12SiO20(BSO) and Bi12GeO20(BGO) at the wavelengths of 1064 and 532 nm were investigated. It was shown that both BSO and BGO crystals possess by positive nonlinear refraction in two investigated spectral ranges (n2BSO=(2.5 ± 0.5)× 10−12 esu, n2BGO=(6.3 ± 1.3)× 10−12 esu at λ equals 1064 nm; n2BSO=(4.4 plusmn; 0.9)× 10−12 esu, n2BGO=(7.4 ± 1.5)× 10−12 esu at λ= 532 nm). The nonlinear absorption was due to three-photon absorption at the wavelength of 1064 nm (β(3ω)BSO=(2.5 ± 0.8)× 10−20cm3W−2, β(3ω)BSO=(4.4 ± 1.3)× 10−20cm3W−2) and two-photon absorption at the wavelength of 532 nm (β(2ω)BSO=(2 ± 0.4)× 10−9cm W−1, β(2ω)BGO=(3.7 ± 0.7)× 10−9cm W−1).

Optical correlation of spatial-frequency-shifted images in a photorefractive BSO correlator.

The optical cross correlation of an image with another image that was spatial-frequency shifted in one dimension was demonstrated in a photorefractive VanderLugt correlator. The first image was stored as a Fourier-transform hologram in a photorefractive Bi12SiO20 crystal (BSO) and was successively correlated with different spatial-frequency-shifted versions of a second image. We implemented the spatial-frequency shift by rotating a galvanometer mirror in an image plane, causing the Fourier transform to be shifted laterally in the BSO. We verified that the resulting operation in the BSO was an accurate complex multiplication of the shifted and the stored Fourier transforms. As many as 20 successive readouts were conducted without measurable erasure of the stored hologram. The dynamic range, saturation behavior, and other performance parameters were measured and are discussed.

Three-Photon Absorption in Photorefractive BSO and BGO Crystals

The possibility of optical limitation of picosecond laser radiation in photorefractive Bi12SiO20 (BSO) and Bi12GeO20 (BGO) crystals at a wavelength of 1064 nm has been demonstrated. It is shown that the mechanism determining the process of optical limitation is three-photon absorption. The coefficients of three-photon absorption have been determined by the Z-scanning method.

Study of nonlinear-optical characteristics of photorefractive BSO and BGO crystals

Nonlinear refraction, nonlinear absorption, and optical limitation are studied in Bi12SiO20 (BSO) and Bi12GeO20(BGO) crystals at the 532-nm emission wavelength of a picosecond Nd : YAG laser.

Slowdown of group velocity of light by means of phase coupling in photorefractive two-wave mixing.

We show theoretically that the group velocity of light can be slowed down by means of phase coupling in the photorefractive two-wave mixing process. It is shown that the group velocity of light propagating in a photorefractive material could be significantly reduced because of a steep variation of the phase-coupling coefficient with respect to the angular frequency difference between two coupling beams in a two-wave mixing process. The results for the case of a photorefractive Bi12SiO20 crystal are presented and discussed in detail.

The growth and photorefractive effect of co‐doped Ce:Cu:BSO crystals

AbstractIn the paper Ce:Cu:BSO crystal has been grown by Czochralski method for the first time with doping CeO2 and CuO into BSO(Bi12SiO20) crystal. The exponential gain coefficient and respond time of Ce:Cu:BSO crystal are measured by two‐wave‐coupling technology. The results indicate that exponential gain coefficient of Ce:Cu:BSO is more than two times as that of non‐doped BSO and the response time exhibits in microsecond level. Furthermore its exponential gain coefficient improves greatly compared with Ce:BSO's at the same doping level of Ce, while its response time is less than Ce:BSO's. The improvement mechanism of photorefractive effect of Ce:Cu:BSO crystal is investigated systematically. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Interferometric fidelity of self-pumped phase conjugation in BaTiO3 and a four-wave mixing set-up with Bi12SiO20 using nanosecond pulses

The fidelity of a self-pumped phase conjugating mirror (SPPCM) in the so-called cat configuration is studied with an interferometric method for a cobalt-doped barium titanate crystal (BaTiO3:Co) under pulse illumination (8 ns, 532 nm). With this SPPCM a phase conjugating four-wave mixing set-up using the sillenite-type crystal Bi12SiO20 (BSO) was realized. It is shown that the fidelity of both phase conjugating processes under pulse illumination nearly reaches the fidelity of continuous-wave experiments.

Effect of optical activity on the self-focusing of light beams in cubic photorefractive crystals

The self-focusing of Gaussian light beams and the propagation of screening spatial solitons in a cubic optically active photorefractive crystal with the (1̄1̄0) cut plane are studied for an arbitrary orientation of an external electric field in this plane. A change in the rotation of the polarisation plane caused by the nonlinear interaction of light with the crystal is studied theoretically. It is shown that optical activity enhances self-focusing in some cases. Screening self-focusing was observed in an incoherently illuminated Bi12SiO20 crystal without additional laser irradiation. The experimental data well agree with the proposed theoretical model.

The influence of annealing at different temperatures and atmospheres on the optical rotation of Bi12SiO20 crystals

Abstract The optical activity changes in Bi 12 SiO 20 (BSO) crystals induced by thermal annealing treatments are studied. It is found that the annealing in vacuum and hydrogen atmosphere causes decreasing of the optical rotation. Thermal treatment annealing induces reduction of Bi-ions to metallic bismuth on the surface as well as oxygen and bismuth diffusion and evaporation is supposed. Annealing in oxygen leads to partial recovery of the oxygen content in the crystals and the optical activity values tends to approach the level of un-annealed BSO crystal.

(2+1)-dimensional soliton formation in photorefractive Bi12SiO20 crystals.

(2+1)-dimensional spatial solitons in Bi12SiO20 (BSO) photorefractive crystals with large optical activity are experimentally demonstrated. The soliton formation when a Gaussian beam is injected at the input has been previously analyzed numerically and then experimentally investigated. We demonstrate analytically, numerically, and experimentally that by applying static electric biases of high values, the polarization rotation accelerates: this acceleration prevents the beam from broadening if the polarization rotation period becomes shorter than the diffraction length. Contemporary to this nonlinear optical activity, an induced birefringence affects the beam polarization state. Analysis of the polarization dynamics shows that the polarization changes nonuniformly across the beam (with a field dependent speed) until about 30-35 kV/cm; above this limit, the whole beam has just one polarization state. Representation on the Poincaré sphere of the polarization dynamics reveals the existence of a stable polarization trajectory closed around a polarization attractor that depends on the linear optical activity and on the photorefractive nonlinearity. The experimental soliton is well described by the analytical solutions already obtained [Fazio et al., Phys. Rev. E 66, 016605 (2002)].

X-ray diffraction topography investigation of the core in Bi12SiO20 crystals

The core in a large Bi12SiO20 crystal as well as the regions free of optical inhomogenities was examined by X-ray double-crystal diffraction topography. It was established that the observed defects in the central core are two-dimensional. The absorption of some impurities as well as the composition changes observed in this area by other authors, should be considered as a consequence of the formation of these defects.

Incoherent-to-coherent IR image converter on the basis of GaAs and Bi12SiO20 crystals

The new model of incoherent-to-coherent infrared (IR) image converter based on a GaAs photoconductor joined to an electro-optic (EO) Bi12SiO20 crystal has been analysed theoretically and experimentally. The possibility of field transfer from the photoconductor to the EO crystal under the IR radiation sufficient for realization of the EO (Pockels) effect in the EO crystal was assessed. Based on the electric field parameters and the parameters of the photoconductor and EO crystal, the threshold sensitivity of the converter was estimated. The experimental photoconductor-EO crystal structure by which IR radiation (0.9-1.5 µm) was converted into the coherent visible radiation was obtained on the basis of theoretical calculations. The measured threshold sensitivity of the converter, 5×10-4 W cm-2, was found to be in the limits of theoretical estimation.