Photorefractive BaTiO3 Research Articles

Phase-conjugate shear interferometer with multiple wavelengths

Optical phase conjugation and two-wavelength recording in a photorefractive crystal BaTiO 3 is used for real-time lateral-shear interferometry. Dispersion in uniaxial BaTiO 3 crystal is used to provide perfect phase matching for two gratings of different spatial frequencies. Theoretical predictions of possible geometries are experimentally verified. The magnification effect and modulation of diffraction efficiency due to recording-reconstruction with different wavelengths are also presented.

Multi-colour-pumped oscillator in photorefractive BaTiO 3

A photorefractive multi-colour-pumped oscillator is described. Oscillation beams, generated by three input beams of different wavelengths, show the effect of competition resulting in their different build-up and behaviour. A theoretical model, based on two sets of coupled differential equations gives good agreement with experimental data.

Phase Defects in a Phase-conjugate Photorefractive-gain Oscillator

Abstract We have performed experiments to establish the origin of phase defects in a phase-conjugate cavity composed of a curved mirror of high reflectivity and a phase-conjugating mirror based on four-wave mixing in photorefractive BaTiO3 pumped by counterpropagating Ar+ laser beams. An intracavity diaphragm was used to change the Fresnel number, thus providing the observation of different transverse structures in the output plane of the photorefractive oscillator.

Two-Wave Mixing and Self-Pumped Phase Conjugation with Photorefractive BaTiO3 at Near-Infrared Wavelengths

We studied the wavelength dependence of the exponential gain coefficient and response time of the two-wave mixing at near-infrared regime with an undoped BaTiO3. We also report a highly efficient self-pumped phase conjugation (SPPC). A 80% SPPC reflectivity at 741 nm was achieved.

Single beam polarization holographic grating recording.

Single beam holographic grating recording, based on the photogalvanic coupling between orthogonal birefringent modes, is demonstrated in a photorefractive BaTiO3 crystal.Received 27 July 1993DOI:https://doi.org/10.1103/PhysRevLett.71.4330©1993 American Physical Society

Self-pumped phase conjugation with BaTiO 3 in a reflection-grating ring configuration

Self-pumped phase conjugation is demonstrated using a photorefractive BaTiO 3 crystal in a reflection-grating ring configuration. The temporal and spatial characteristics of the phase-conjugate wave are found to depend on the direction of the crystal.

Heterodyne detection of weak optical wavefronts burried in a photorefractive fanning noise

Weak signals, initially burried in the beam fanning noise of photorefractive amplifiers can be efficiently detected by combining the temporal filtering properties of coherent receivers with a spatial averaging over the random noise distribution that occurs from photorefractive effects. This is demonstrated by modulating in time the signal or the pump beam. Theoretical and experimental investigations using photorefractive BaTiO 3 in four different configurations are reported and compared.

Spatial Resolution and Channel Coupling in a Phase-conjugate Ring-resonator

Abstract We describe our study of the spatial resolution of a phase-conjugating ring-resonator (PCR) consisting of a Sagnac interferometer and a phase-conjugating mirror based on four-wave mixing in photorefractive BaTiO3. The use of optical image processing systems depends on the amount of information channels and the nonlinear coupling between the channels. The spatial resolution or the number of independent pixels is important to describe any image processing system. If the gain of the phase-conjugating mirror is higher than the losses in the passive part of the system, then the system exceeds the threshold, and without any externally incident signal the resonator shows the effect of self-oscillation. From the analysis of this self-oscillation pattern we have calculated the spatial resolution of the PCR. Additionally, we try to investigate the pixel coupling of the system by defining channels in the resonator. By changing the geometrical set-up of the system it is possible to observe a controlled coupl...

Dark build-up of holograms in BaTiO3 after recording

Holograms recorded under suitable conditions in photorefractive BaTiO3 exhibit an unusual dark build-up. The diffraction efficiency increases by some orders of magnitude after the recording beams are switched off, and then steadily decreases afterwards. An interpretation of this effect in terms of a two-center charge transport model is given.

Waveguide mutually pumped phase conjugators

The operation of the bridge mutually pumped phase conjugator is reported in a planar waveguide structure in photorefractive BaTiO(3). The waveguide was fabricated by the technique of ion implantation, using 1.5-MeVH(+) ions at a dose of 10(16) ions/cm(2). An order of magnitude decrease in response time is observed in the waveguide as compared with typical values obtained in bulk crystals, probably as a result of a combination of the optical confinement within the waveguide and possible modification of the charge-transport properties induced by the implantation process.

Residue lookup table processor using an optical phase conjugation correlator

Described is a new optical residue lookup table (LUT) processor that is based on the residue LUT from an optical phase-conjugated correlation output of spatial position-encoded input vector patterns in a photorefractive BaTiO(3) correlator and a holographic mapping unit to group the same residue numbers. Some preliminary experimental results of these proposed techniques are presented and discussed.

Thermal gratings and pyroelectrically produced charge redistribution in BaTiO_3 and KNbO_3

The influence of a pyroelectric charge-driving force on photorefractive currents is demonstrated experimentally for the first time to my knowledge. Illumination of photorefractive BaTiO3 and KNbO3 crystals by two intersecting coherent light pulses (light wavelength λl = 532 nm) induces thermal gratings. A spatially modulated pyroelectric field arises. Photoexcited carriers move in this field and tend to compensate for it. The pyroelectric field vanishes after termination of the pulse with a characteristic decay time, and redistributed charge remains. Measurements demonstrate that this pyroelectric charge-transport driving force can be much stronger than diffusion for fringe spacings greater than 2 μm. From this new charge-transport mechanism I derive a promising proposal for hologram writing and reading at the same wavelength without erasure.

Theoretical study of Fe doping and oxidation–reduction influence on the photorefractive effect in BaTiO_3

We numerically solve charge-transport and Poisson equations for photorefractive BaTiO3 single crystals with a band model, using four impurity levels, Fe2+–Fe3+, Fe3+–Fe4+, VO••–VO•, and VO•-VOx. Densities and photoinduced spatial distributions of each population are computed as a function of annealing O partial pressure. Space-charge field and beam-coupling gain are also computed as a function of annealing O partial pressure, temperature, Fe concentration, grating wave vector, and light intensity. We discuss the intervening mechanism of impurity centers and the correlations between experimental conditions of crystal growth, oxidation–reduction treatments, and measurement parameters.

Non-steady-state photocurrent technique for the characterization of photorefractive BaTiO 3

Non-steady-state photocurrent measurements are carried out with a photorefractive BaTiO 3 crystal at the light wavelength 514 nm. We obtain the diffusion length for different crystal orientations, and derive the mobility ratio for charge carrier migration parallel and perpendicular to the c-axis. The frequency dependence of the photocurrent reveals two characteristic times.

Double phase-conjugate mirror with sixfold gain in photorefractive BaTiO_3 at near-infrared wavelengths

We describe incoherent beam coupling using the double phase-conjugate mirror arrangement between a laser diode and a Ti:sapphire laser at the near-infrared wavelengths of ~800nm using a nominally undoped sample of BaTiO3. We report phase-conjugate reflectivities of greater than 6 times, which we believe to be the highest reported to date at these wavelengths. We also examine the fidelity of the phase-conjugate beam and the wavelength response of the double-color-pumped oscillator.

Noise reduction in image amplification in photorefractive BaTiO 3

Based on the feature that a signal grating has faster formation rate than noise gratings, we have demonstrated that in the presence of a beam with a frequency different from that of the pump beam, it is possible to reduce the optical noise while maintaining high gain for the two-wave mixing image amplification.

Forward mixing of two mutually incoherent beams in a photorefractive crystal

The Letter proposes and experimentally demonstrates the coupling, in the forward direction of two mutually incoherent beams in a photorefractive BaTiO3 crystal. The photoinduced grating exhibits a diffraction efficiency of 0.3% at 633 nm.

Phase-conjugate fluorozirconate fiber laser operating at 800 nm

We report phase-conjugate feedback into a fluorozirconate optical fiber amplifier at infrared wavelengths. By using a semiconductor laser diode at 807 nm, a grating is established in photorefractive BaTiO(3) that, in the ring configuration, provides feedback into the amplifier necessary for laser action. Once written, the grating is self-sustaining, and lasing is observed even after the laser diode is removed.

Comparison of BaTiO3 optical novelty filter and photothermal lensing configurations in photothermal experiments

Photorefractive BaTIO3 is used as an optical novelty filter to highlight the high spatial frequency components of the photothermal signal. A real-time phase grating recorded in BaTIO3 acts as a matched rejection spatial filter for the probe laser. This reduces the stationary background from the optical signals thereby increasing signal contrast ratios. Rejection of the monotonous stationary signal provides a powerful means of improving the photothermal signal. This paper describes the construction of this novel apparatus and the experiments performed in order to compare its performance with photothermal lensing results. A theory that explains photothermal signal filtering with BaTIO3 as an adaptive spatial frequency filter is presented. Results comparing the optical signals obtained in a photothermal lensing experiments and those obtained in the BaTIO3 optical novelty filter experiments are presented. The optical novelty filter signals demonstrate a remarkable improvement in the signal contrasts for moderate photothermal-induced phase shifts.

EoP202. Spatial resolution of a phase-conjugate ring-resonator

Abstract We describe our study of the spatial resolution of a phase-conjugating ring-resonator (PCR) consisting of a Sagnac interferometer and a phase-conjugating mirror (PCM) based on four-wave mixing in photorefractive BaTiO3. The use of optical image processing systems depends on the amount of information channels and the nonlinear coupling between the channels. We examined the contrast function of a set of incoming signals which depends on the gain of the PCR and the feedback ratio of the whole system. We obtained about 105 independent channels within our system. Additionally, we tried to investigate the transfer function of the system by comparing the power spectrum of the incoming signal and the output signal. By changing the geometrical setup of the system it should be possible to observe a higher resolution. On the other hand it is possible to control the coupling strength by varying the linear feedback part of the PCR.