Two-wave mixing of phase-modulated beams in GaP under a dc electric field

Two-wave mixing of phase-modulated light beams in crystals of cubic symmetry is analyzed on the basis of the vectorial theory of light diffraction. We derive an analytical expression for phase-to-intensity transformation in crystals of the 43m point group of symmetry, which differs from the previously obtained solution based on the scalar approach. The most effective transformation is achieved when the amplitude of the space-charge-field grating is equal to the quarter-wave field. It is shown that the space-charge-field grating created in GaP semi-insulating crystal at the wavelength of 632 nm is much smaller than can be predicted from the one-level band-transport model.     

Photorefractive effect in sillenite crystals with shallow traps in a sign-alternating electric field

The results of a theoretical analysis of the photorefractive response in crystals with shallow traps to in a sign-alternating, square-wave electric field are presented. The numerical analysis method developed imposes no restrictions on the frequency of the external field and the period of the photorefractive grating. The parameters characterizing deep donor and shallow trap centers are estimated on the basis of investigations of two-beam interaction in a Bi₁₂SiO₂₀:Cd crystal with the application of a sign-alternating, square-wave electric field. Fiz. Tverd. Tela (St. Petersburg) 40, 2037–2043 (November 1998)     

Nonlinearity of a response in photorefractive crystals with a square-wave applied field

The space-charge-field formation in a photorefractive crystal illuminated by a one-dimensional light pattern is studied when an alternating square-wave electric field is applied to the crystal. We derive the general nonlinear equation for the time-averaged distribution of the space-charge field and employ the simplified versions of this equation to analyze the space-charge-field formation in the case of a Gaussian beam and interference light pattern. The borders of the applicability of simplified equations and analytic expressions to describe a self-action of light beams and the large modulation effects under two-beam coupling are estimated from the numerical calculations. Received: 18 November 1998 / Revised version: 26 January 1999 / Published online: 12 April 1999     

Formation rate of vapor bubbles in magnetic fluid boiling at a single vaporization center: Measuring technique and experimental setup

A technique for measuring the bubbling rate during magnetic fluid boiling at a single vaporization center in an external uniform magnetic field is suggested and proved, and an experimental setup is designed based on this technique. It is shown that the magnetic field substantially influences the rate of detachment of the bubbles in a wide range of temperatures below the saturation temperature. The diameter of the vapor bubble at which it separates in the magnetic field (separation diameter) is estimated.     

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.     

Vector Approach to Calculating Space-Charge Fields in Crystals withntrast Light Interference Pattern

A new method for calculating space-charge fields in photorefractive crystals with shallow-lying traps illuminated by a light interference pattern of arbitrary contrast and shape is suggested. A space-charge field in a BSO:Cd crystal with shallow-lying traps illuminated by a sine light interference pattern with the high contrast m = 0.99 is calculated.     

Determination of the Space-Charge Field Amplitude by the Phase Modulation Method

Results of experimental and theoretical investigations into the conversion of the phase modulation of light into its intensity modulation in photorefractive crystals are presented. Based on the vector diffraction theory, an analytical expression describing a phase demodulation in crystals in an external electric field applied in an arbitrary direction is derived. The phase demodulation is used to determine the space-charge field amplitude in cubic crystals. It is demonstrated that the space-charge magnitude measured in GaP and Bi₁₂TiO₂₀ crystals is less than that predicted by the Kukhtarev single-level model.     

Detection of small phase modulation using two-wave mixing in photorefractive crystals

Two-wave mixing of phase-modulated beams in photorefractive crystals under a dc electric field is studied both theoretically and experimentally. Based on the vectorial theory of light diffraction in crystals of cubic symmetry, we derived an analytical expression that describes the phase demodulation in crystals with an arbitrarily oriented electric field. The phase-demodulation technique was used for estimation of the space-charge field created in photorefractive crystals. It is shown that the space-charge-field grating created in GaP and Bi₁₂TiO₂₀ crystals is much smaller than that predicted from the one-level band-transport model of the photorefractive effect. Received: 12 December 2000 / Revised version: 8 February 2001 / Published online: 27 April 2001