Photorefractive LiNbO3 Crystal Research Articles

Single beam one-way imaging through a thick dynamic turbulent medium

A new method to record an image through a thick dynamic phase distorting medium by using a photorefractive LiNbO3 crystal is demonstrated. The method uses only one beam of light, the object light. By making use of the photorefractive fanning effect, gratings are formed in the LiNbO3 crystal through the interference between the object light and its own fanning light. Because the time scale of the distorting fluctuation is much shorter than the writing time of the LiNbO3 crystal, the fluctuated light does not induce any fanning. Therefore only the static portion of the image is recorded in the crystal, and the intensity distribution of the image can then be reconstructed at any later time.

One-beam recording in a LiNbO_3 crystal

We propose a new way to record images in a photorefractive LiNbO3 crystal. This method involves only a single object light without any reference light. We believe that the recording is attained by fanning holograms that result from interference between the object light and its scattered light. Although volume gratings are involved, the recorded pattern can be viewed not only with a laser light beam that is incident over a certain angular range but also with white light.

Nearly 100% diffraction efficiency fixed holograms in oxidized iron-doped LiNbO3 crystals using self-stabilized recording technique

We analyse the advantages and limitations of self-stabilized holographic recording for fixing in photorefractive iron-doped LiNbO3 crystals. We study the effect of the degree of oxidation on the development of the fixed grating, confirm the importance of highly oxidized crystals to obtain fixed holograms with high diffraction efficiency and put it on a quantitative basis. We also discuss the effect of iron-concentration and the way oxidation may introduce dopant-saturation effects in the recording. Accounting on the different parameters here considered we propose a very simple and well performing procedure to produce nearly 100% diffraction efficiency fixed gratings.

Two-way coherent image transfer using photorefractive crystals

We present a setup that transfers 2-D images between two ports. By using a photorefractive LiNbO3 crystal and a BaTiO3 crystal, we are able to transfer images either way without making any change in the experimental layout. The resolutions of the device are 10.1 and 6.4 lp/mm for the two transferring directions, respectively.

Theory of variable-angle switch by anisotropic diffraction in photorefractive LiNbO 3 crystal

Summary Based on the anisotropic diffraction of photorefractive LiNbO3 crystal, we present the theoretical result of a variable-angle switch. The deflection angle of the proposed switch can be changed by changing value of writing angles of the grating, and the result shows that the deflection angle can change in the range of −1° to +1°. The proposed theory can be used in switching design.

PHOTOINDUCED OPTICAL AND ELECTRICAL HIGH-VOLTAGE PULSATIONS AND PATTERN FORMATION IN PHOTOREFRACTIVE CRYSTALS

We review our results on conversion of CW laser Ar-ion beam power into pulsating multi-channel outputs: optical, electric and piezoelectric with simultaneous dynamic pattern formation. We show, that electrical pulsations generate high-voltage signals that may be used as a driving voltage for the conventional electro-optical modulator. We have also demonstrated the possibility of synchronization of two optical pulsators, through regulated optical coupling in a photorefractive LiNbO3 crystal. Spatial distribution of scattered light is self-organized in different patterns (hexagonal and cross-type).

Holographic read - write projector of video images

We demonstrate two real-time, read-write holographic projectors of video images based on photorefractive materials. A photorefractive crystal holographically records multiple, angularly multiplexed 2D images. By sequentially reconstructing each pre-recorded image a holographic video is created. In first setup the 2D image of an LCD screen is holographicaly recorded in a photorefractive LiNbO3 crystal. In the second setup the Fourier transform of the LCD screen is recoded in the crystal. A detailed comparison of the two setups along with a number of videos is provided. The Fourier transform recording is superior in image quality compared to the direct image recording.

Threshold effect for photorefractive light-induced scattering and signal beam amplification in doped LiNbO3 crystals

In this article, we have studied experimentally the threshold effect of incident light intensity for the photorefractive light-induced scattering and signal beam amplification in doped LiNbO3 crystals. Our results show that the signal beam can be most effectively amplified for a specific pump light intensity when the threshold effect of incident light intensity for photorefractive light-induced scattering is taken into account in doped LiNbO3 crystals. Doping the LiNbO3 crystal with suitable concentration of Fe and damage-resistant dopants will provide an effective way to control the photorefractive properties of LiNbO3 crystal. We demonstrated the advantage of the fanning-noise-free double-doped photorefractive LiNbO3 crystals for three-dimensional storage. This method to suppress the fanning noise is very simple and convenient to practice.

A narrow-band interference filter with photorefractive LiNbO3

A narrow-bandwidth interference filter has been developed using volume holography in photorefractive LiNbO3 crystals. The device works as a Bragg reflector using a volume hologram recorded, fixed and developed in a LiNbO3 sample. With a 2 mm thick LiNbO3 plate the following performances have been achieved: a peak reflectivity above 32%, a full-width at half-maximum bandwidth below 0.05 nm, an angular field of view of about 3 degrees and a peak wavelength of 518.45 nm (for green Ar laser writing wavelength). These performances compare well with that exhibited by the conventional Lyot-Ohman and Solc filters. A complete explanation of the fabrication procedure is given, including practical details needed for producing such an efficiency with fixed holograms in LiNbO3.

Reduction of photorefractive LiNbO3crystals in powdered Li2CO3

Reduction of photorefractive LiNbO₃crystals in powdered Li₂CO₃

Thermodynamic analysis and formation enthalpy calculation of oxygen vacancy defect in doped lithium niobate crystals

Based on the thermodynamic analysis of oxygen vacancy defects in lithium niobate (LiNbO3 (LN)) and the data of thermogravimetric experiment, the formation enthalpies of congruent and several rare-earth (RE) doped LN crystals have been calculated. It was found that the formation enthalpy of oxygen vacancies can be decreased evidently by doping with valence-changeable RE ions. The experimental results were discussed and a new reduction process for photorefractive LN crystals at a relatively low temperature was proposed, and the reduction-treated crystals showed good effect in practical use.

Polarization restoration by phase conjugation in photorefractive crystals

Theoretical and experimental investigations are reported of polarization phase conjugation in a photorefractive LiNbO3 crystal. It is shown that the photogalvanic mechanism of hologram formation by orthogonally polarized beams can ensure complete restoration of the polarization as a result of a degenerate four-wave interaction.

Dynamics of parametric holographic-type scattering of light

A study was made of the dynamics of degenerate parametric scattering of light in photorefractive LiNbO3 crystals. A numerical solution was obtained of a system of reduced equations for the amplitudes of the interacting waves, which described well the experimental results. Three characteristic stages of the development of the scattering were identified: spontaneous, stimulated, and saturation. The experimentally determined spectral–angular brightness of the noise seed radiation, which induced scattering in the spontaneous regime, was considerably higher than the calculated brightness resulting from the Rayleigh scattering of pump radiation by optical inhomogeneities of the investigated crystal.

Photovoltaic spatial light modulator

A novel concept for implementing a high-resolution spatial light modulator using a thin slab of photorefractive LiNbO3 crystal is described. This method uses the photovoltaic effect to impress phase information onto the crystal without the use of holography where coherent reference beams are required. Experimental demonstration as well as an analysis of the operation and performance of the device are given.