ABSTRACT
We develop the idea of critical enhancement of the photorefractive response near the threshold of parametric excitation of space-charge waves (the spatial subharmonics) taking into account the vectorial character of beam coupling and a fairly strong broadening of the nonlinear resonance owing to light absorption. The results of our calculations are a description of the measurable characteristics of critical enhancement and optimization of the experimental conditions for detection of anomalously high amplification gain factors in cubic Bi(12)SiO(20) crystals.
ABSTRACT
We investigate here both theoretically and experimentally light-induced scattering in (111)-cut Bi12TiO20 crystals with an external ac field. Our simple analytic solution, which is nearly as precise as the numeric one, allows us to recognize the following otherwise hidden general features. Without the elasto-optic contribution, the scattering patterns are identical for the same value of xi=zeta(0)+(2/3)straight phi(p), where straight phi(p) is the initial polarization angle and zeta(0) is the angle of the external field. With the elasto-optic contribution, the scattering patterns for the same xi are still very similar. For xi not equal0, the scattering patterns depend differently on the elasto-optic coefficients p(12) and p(13) so that in principle p(12) and p(13) can be measured by purely holographic experiments. On the experimental side, we present scattering patterns for xi=0 and +/-30 degrees, showing thereby the similarity of the scattering patterns for equal values of xi. In all cases, we obtain good qualitative agreement of our analytic and numeric calculations with the experimental findings.
ABSTRACT
We present an analytical theory of vectorial wave coupling in photorefractive cubic crystals which are, in general, optically active. The theory is based on the systematic use of the spatial symmetry properties and the apparatus of the Pauli operators to deal with two-dimensional vectors and matrices. It allows one to give a unified description of a wide spectrum of photorefractive phenomena, including the efficiency and polarization properties of Bragg diffraction, polarization two-beam coupling enhanced by ac fields, the influence of the photoelastic effect, etc. Applications of the theory to crystals of the sillenite family and to particular photorefractive phenomena are given. A good qualitative agreement between the theoretical predictions and experimental data for Bi12TiO20 (BTO) crystals is shown.
ABSTRACT
We show theoretically and experimentally that switching an applied square-wave field produces strong and short pulses of the outgoing signal during two-wave mixing in sillenite crystals. These pulses originate from the strong effect of the field on the optical eigenmodes and can be used in new optical schemes based on time-separated recording and readout processes.
