ABSTRACT
We consider a possibility to create a metamaterial with nonlinear magnetic response in the microwave frequency range. Such a metamaterial is a regular periodic three-dimensional-array of resonant conductive elements with diodes as nonlinear insertions. We calculate the arising quadratic nonlinear susceptibility and show how it is controlled by the properties and arrangement of the structure elements as well as by the type and characteristics of the diode. We discuss the requirements for the diode necessary to optimize the nonlinear response of the proposed metamaterial.
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.
ABSTRACT
Our experiment shows that stimulated backscattering from photorefractive LiNbO(3):Fe crystals occurs not only for an orientation of the polar axis that is parallel to the input beam but also for the opposite orientation, in which the spatial amplification of seed scattering through pi/2-shifted gratings is impossible. In the latter case scattering exhibits pronounced noise properties. We show analytically and numerically that the observed regularities are explained by a model including a source of low-frequency temporal noise for the space-charge field and a strong photovoltaic effect.
ABSTRACT
We demonstrate a novel method to enhance the phase resolution of a barium titanate beam-fanning novelty filter by means of an external phase shift in one part of the signal wave. The new technique is described theoretically on the basis of the coupled-wave theory. Experimental results are presented to demonstrate the behavior and the advantages of the novel device for the evaluation of spatial and temporal phase changes in incident signal waves.
ABSTRACT
It is shown that a resonance-enhanced moving grating in a photorefractive crystal is unstable against the growth of weakly damped space-charge waves. The threshold of the instability and the rate of exponential growth of the waves are found.
ABSTRACT
It is shown that spatial gratings in photorefractive crystals, induced by the standing interference pattern of two coherent waves and an external alternating electric field, may be unstable against the excitation of weakly damped eigenmodes. The dependence of the exponential rate of growth of the instability on experimental parameters and crystal characteristics is investigated. The instability influences the amplification of the photorefractive sensitivity by an ac field. A comparison is made between theoretical results and experimental data.
ABSTRACT
The photorefractive recording process as described by Kukhtarev's material equations is investigated for large modulation depths. We find that for modulation 1 the density N(+)(D) of ionized traps at the dark sites is zero in the steady state if dark conductivity can be neglected. Therefore, in this case, it is essential to take the depletion of ionized traps into account.
