Phase conjugation in BaTiO 3 by use of the indirect photorefractive coupling of orthogonally polarized light waves

A phase-conjugate wave is generated when an ordinary (extraordinary) signal wave is mixed with two counterpropagating extraordinary (ordinary) waves in the plane normal to the BaTiO3 polar axis. The photorefractive grating that couples the ordinary and the extraordinary waves appears if the incident waves induce a noticeable conical parametric scattering; this grating is a difference grating of many noisy scattering gratings recorded by means of the usual diffusion-mediated charge transport. For comparable intensities of signal and pump waves this type of nonlinear wave mixing is much more efficient than that which is due to the circular bulk photovoltaic effect.

Instability of single-frequency operation in semilinear photorefractive coherent oscillators.

The transition of the single-frequency oscillation of a semilinear photorefractive coherent oscillator for sufficiently large coupling strengths into two-frequency oscillation is predicted and is observed experimentally. The critical value of the coupling strength at which the bifurcation occurs is a function of pump intensity ratio and cavity losses. The supercritical bifurcation in the oscillation spectrum is analogous to the second-order phase transition.

Supplementary optical phase transition in photorefractive coherent oscillator

The semilinear photorefractive coherent oscillator with two counterpropagating pump waves may exhibit two optical phase transitions: one from a disordered state of wide-angle photorefractive scattering into a high-ordered state with the immobile photorefractive grating and the other one from the state with immobile grating into the state with two moving photorefractive gratings. We show, both experimentally and from calculations, that two these phase transitions are the second-order phase transitions.

Polarization backward-wave four-wave mixing in BaTiO_3:Fe using the photovoltaic effect

We report the first study to our knowledge of polarization backward-wave four-wave mixing in a BaTiO3:Fe crystal and compare the results of our measurements with the calculations performed within the model of photovoltaic charge transport. Two identically polarized pump waves and one orthogonally polarized signal wave are sent to a sample in a plane normal to the crystal’s C axis; a phase-conjugate wave with polarization identical to that of the signal wave is generated. With a 2-mm-thick sample a phase-conjugate reflectivity Rpc≈0.01 is reached; for a 1-cm-thick sample, amplified reflection should be possible.

Photorefractive amplifier-converter and coherent oscillator with nonexponential gain

For some parametric interactions with identically zero exponential gain for the signal wave the intensity of the idler wave can grow as a second power of the propagation coordinate. Such an amplification is revealed for the parametric mixing of four copropagating waves in BaTiO3; two of them are ordinarily polarized and the two others are extraordinarily polarized. This mixing is used to build up a coherent oscillator. A reasonable qualitative agreement of the experimental results with the calculated data is demonstrated.

Parametric coherent oscillation with feedback via an orthogonally polarized wave

Coherent light amplification with photorefractive crystals may be a consequence of several frequency degenerate (or nearly degenerate) processes of nonlinear wave mixing : It appears for two- beam coupling in the crystals with diffusion-driven charge transport [1] or transport via circular photovoltaic currents [2].

Dynamique d'un oscillateur photoréfractif : instabilités et analogie avec la loi de Curie-Weiss

La dynamique et l'etat stationnaire du faisceau issu d'une cavite oscillante comprenant un cristal non-lineaire de titanate de baryum utilise en tant que miroir a conjugaison de phase sont etudies. Le parametre du systeme etant le gain du milieu non-lineaire, les dependances de l'intensite de l'oscillation et de l'inverse du temps de reponse sont similaires aux lois de Curie en physique du solide.

Optical hysteresis in a semilinear photorefractive coherent oscillator

International audience; High contrast optical bistability is found experimentally in the pump-ratio dependences of the output intensity of a semilinear photorefractive coherent oscillator with two counterpropagating pump waves. The data are in qualitative agreement with the results of calculation.

Phase Conjugation in BaTiO/sub 3/ Using Orthogonally Polarized Light Waves

Manifestation of Curie-Weiss law for optical phase transition

Considerable slowing down is observed for both the temporal development of the coherent oscillation slightly above the threshold and the refractive index grating decay slightly below the threshold for a semilinear photorefractive oscillator with two counter-propagating pump waves. It is shown that in the vicinity of the threshold the reciprocal characteristic time is a linear function of deviation from the threshold coupling strength. This behaviour is similar to an empirical Curie–Weiss law and points to the analogy of the oscillation threshold to a second-order phase transition.