Jean-Michel Jonathan

Time-resolved buildup of a photorefractive grating induced in Bi 12 SiO 20 by picosecond light pulses

Photorefractive gratings are induced with picosecond light pulses in a BSO crystal. Both experiment and calculations show a buildup of the effect governed by a diffusion of the excited charge carriers that occurs after illumination.

43 m photorefractive materials in energy transfer experiments

Abstract The photorefractive effect in 4 3 m crystals shows specific symmetries in its dependence upon wave polarizations and crystal orientation. Theoretical predictions and experimental verification in semi-insulating gallium arsenide in the nanosecond regime at 1.06 μm are given.

Characterization of a photorefractive rhodium doped barium titanate at 1.06 μm

Abstract We characterize Rh:BaTiO 3 by cw two-beam coupling experiments at 1.06 μm. We demonstrate that all our measurements are well described by a single-carrier, single-site model as soon as the incident intensity is large enough. The effective trap density is found to be equal to N eff = 6 × 10 16 cm −3 and the maximum measured gain is 23 cm −1 . At 20 W cm −2 with a measured absorption of 0.15 cm −1 , the time constant is 75 s.

Two-wave mixing in photorefractive BaTiO 3 :Rh at 1.06 µm in the nanosecond regime

We present two-beam coupling experiments in the nanosecond regime at 1.06 mum , using photorefractive BaTiO(3):Rh. The maximum observed exponential gain coefficient is 14.2 cm(-1) . No intensity-dependent electron-hole competition and no strong saturation of the photoionized charge carriers are observed for intensities of less than 20MW cm(-2) . The energy required for recording the photorefractive grating is not significantly different in the nanosecond and the cw regimes.

Polarization holography with photoinduced anisotropy in bacteriorhodopsin

Polarization holographic gratings transform the polarization state of an incident wavefront. We have studied the diffraction properties of polarization gratings, formed with two orthogonal linearly or circularly polarized waves. For a polarization modulation recorded in the organic material bacteriorhodopsin, the diffraction efficiency and the diffracted wave polarization strongly depend on the polarization state of the read- out wave. We have given a simple theoretical treatment using the Fraun- hofer diffraction integral. The experimental results have been interpreted in terms of this simplified model.

Self-pumped phase conjugation in a ring cavity at 1.06 μm in cw and nanosecond regimes using photorefractive BaTiO3:Rh

Abstract We present self-pumped phase conjugation experiments in a ring cavity at 1.06 μm in a BaTiO 3 :Rh crystal both in the cw and in the nanosecond regime. The measured reflectivities are respectively 50% and 66%. At 4 W cm −2 of cw illumination, it only takes 90 s to reach the steady state. A preliminary experiment of correction of the focusing effect of a lens is reported.

Whole-beam method analysis of photorefractive effect in correlators

Abstract The equations of the whole-beam method in photorefractive media have been derived and used to analyze the performances of a photorefractive correlator in the geometry of a joint transform correlator. Taken into account are the nonuniform, two-dimensional and nonperiodic illumination. The derivation of the steady state space charge field is detailed. The induced index variation, a nonlinear function of the illumination, exhibits a term which is not predicted before. Experimental evidence for that effect is given.

Photorefractive effect in the Fourier plane

Abstract On the basis of the Whole Beam Method, we describe the steady state photorefractive effect in optical devices where the crystal illumination is not a uniform interference pattern. The example of BSO, sitting in the Fourier plane of the two images of a Joint Transform Optical Correlator is given as an illustration.

Analysis Of The Energy Dependence Of The Photorefractive Gain In Nanosecond Wave Mixing In Semiconductor Crystals.

Based on the results of two wave-mixing experiments in the nanosecond regime conducted in the semi-insulating crystal InP:Fe we present an analysis of the build-up of the photoinduced space charge field that governs the photorefractive effect. A numerical integration of the materials differential equations is carried out taking into account charge transport by holes and electrons. Competition between drift and diffusion, and between hole and electron charge transport limits the coupling gain. The time evolution and the role of the important quantities are explained by the use of appropriate approximations.

Effect Of Compensation On The Amplification Of Photorefractive Two Beam Coupling By Alternating Electric Field

A general expression for the photorefractive gain under step like electric field is derived. It shows the gain dependence on the applied field frequency which is confirmed experimentally. We show how optimum gain enhancement is achieved by adjusting the illumination and the field frequency to the characteristic times of the crystal. Simultaneous contribution of holes and electrons is also considered to explain reduced values of the gain observed in some cases.