Holograms In Photorefractive Crystals Research Articles

Six-channel adaptive fibre-optic interferometer

We have proposed and analysed a scheme for the multiplexing of orthogonal dynamic holograms in photorefractive crystals which ensures almost zero cross talk between the holographic channelsupon phase demodulation. A six-channel adaptive fibre-optic interferometer was built, and the detection limit for small phase fluctuations in the channels of the interferometer was determined to be 2.1 × 10-8 rad W1/2 Hz-1/2. The channel multiplexing capacity of the interferometer was estimated. The formation of 70 channels such that their optical fields completely overlap in the crystal reduces the relative detection limit in the working channel by just 10 %. We found conditions under which the maximum cross talk between the channels was within the intrinsic noise level in the channels (-47 dB).

A thermostatic controller for investigating temperature dependencies of optical effects in crystals

A thermostatic controller used for investigating temperature dependencies of optical absorption, its photoinduced changes, and efficiency of two-beam interactions on reflecting holograms in photorefractive crystals is described. The thermostatic controller is intended to specify the rate of temperature changes of the crystals under investigation and stabilize the sample temperature in the range of +5 to +110°C with an accuracy of ±0.5°C.

Mutual transformation of light waves by reflection holograms in photorefractive crystals of the $$\bar 43m$$ symmetry

The mutual transformation of light waves in the case of their simultaneous diffraction from a bulk reflection phase hologram, which was formed in a cubic photorefractive crystal of the \(\bar 43m\) symmetry class, has been studied. The indicator surfaces of the polarization-optimized values of the relative intensity of the object wave, which make it possible to determine the amplification of this wave for any crystal cut, are constructed. The linear polarization azimuths at which the energy exchange between the light waves reaches a maximum are found numerically for crystals of different cuts.

Wavelength multiplexing and demultiplexing with one single volume hologram in photorefractive crystal

Based on anisotropic diffraction of a volume phase grating in a photorefractive crystal, we theoretically discuss an optical multi- and demultiplexing scheme implemented by one single grating in photorefractive LiNbO3 crystal. It shows that our scheme can simultaneously demultiplex 93 channels in the telecommunication wavelength around 1550 nm. Using only one grating to realize WDM can avoid the multiple exposure problems encountered by multiple hologram scheme. Moreover, in our scheme, the transmitted and diffracted beams are orthogonal to each other, thus we don't need to use a normal recording and readout structure. Our theoretical results can be used in the design of a WDM device.

Optimal Geometry for Fast and Efficient Hologram Recording in Photorefractive Crystal

Theoretical analysis of optical focusing system for recording dynamic hologram in photorefractive crystal by Gaussian light beams is carried out. Relations between parameters of the crystal, recording beams and lenses have been found. Optimal focusing system constructed taking into account obtained relations allows us to record fast and simultaneously highly efficient dynamic hologram in photorefractive crystal with low-power continuous-wave lasers.

Selective erasure of speckle-multiplexed holograms by use of a double Mach-Zehnder interferometric arrangement

A novel method to selectively erase and update speckle-multiplexed holograms in photorefractive crystals by use of a double Mach-Zehnder (DMZ) interferometric arrangement is presented. The DMZ arrangement automatically produces a pair of pi-phase-shifted interference patterns used for holographic recording, erasure, and update operations with a fairly simple optical configuration that consists of a commonly used dielectric multilayer beam splitter and two mirrors. The recording and the erasure conditions required for erasing a photorefractive hologram quickly and completely are discussed by calculating the temporal property of the hologram buildup and decay using the time-dependent coupled-wave equations. An experiment is also performed, in which arbitrary holograms in speckle-multiplexed holograms are selectively erased and updated with the simple DMZ optical configuration.

Continuous monitoring of a surface slope by real-time shearing interferometry with a photorefractive crystal

We propose and demonstrate a new technique for measuring the temporal variations of the surface slope of an object. This real-time shearometric arrangement takes advantage of the dynamic properties of holograms in photorefractive crystals. The accuracy of the measurements should make this technique suitable for real-time structural intensity determinations.

Wide angular aperture holograms in photorefractive crystals by the use of orthogonally polarized write and read beams

We demonstrate a method of simultaneous holographic recording and readout in photorefractive crystals that provides high write-read beam isolation and wide angular bandwidth. The method uses orthogonally polarized read and write beams and parallel tangent diffraction geometry near the equal curvature condition to provide spatially separable, orthogonally polarized diffracted output beams with high isolation and wide Bragg-matched angular bandwidth. The available angular bandwidth of this read-write technique is analyzed, simulated, and experimentally investigated. The measured angular bandwidth internal to the crystal is approximately 18° × 6° for our 45°-cut BaTiO(3) crystal, yet the entire hologram still demonstrates high Bragg selectivity. In contrast, traditional nonparallel-tangent geometries yield angular apertures of the order of 1° × 4°.

Spatial differentiation of optical images using selective erasure of photorefractive holograms

We propose and demonstrate a novel technique of spatial differentiation of optical images based on the selective erasure of holograms in photorefractive crystals using a composite filter which consists of an amplitude and a phase filter. The net filter is realized by controlling the modulation depth, amplitude of a photorefractive grating using a one-dimensional Gaussian erasing beam in conjunction with a phase filter in the reading beam's path. Experimental results are presented and compared with other type of filter.

High‐resolution surface sensing device using Bragg diffraction from multiplexed holograms in photorefractive crystal

A novel high‐resolution surface sensing device is developed and demonstrated, which utilizes Bragg diffraction from the volume holograms in the photorefractive BaTiO3 crystal. In this device, the angular information of a surface is obtained as a diffraction pattern from the multiplexed holograms stored in the crystal. The resolution of this device is as high as submilliradian due to the Bragg selectivity. Additionally, a new method of surface structure comparison between two samples is also demonstrated using this device, which is applicable to the nondestructive surface inspection of optical components.

Feasibility of using dynamic holography in measurement of the correlation dimensionality of the path of a process

A method is proposed for experimental measurement of the correlation dimensionality of attractions in dynamic systems. This method is based on the recording of holograms in photorefractive crystals and it can operate in real time. There are no limitations on the dimensionality to be measured.

Positive and negative feedback effects of four-wave mixing in photorefractive crystals with two active centres

Based on a two-level model of optical transitions, the problem of positive and negative feedback effects during simultaneous reading and writing of dynamic holograms in photorefractive crystals has been solved analytically. The diffraction efficiency and the gain coefficient are shown to be nonlinear functions of the readout beam intensity and are nonreciprocal with respect to the readout from the two input ports. The readout beam intensity value that affects a previously recorded grating is shown to depend on microscopic parameters such as the cross-section of photoionization, the recombination coefficient and the concentration of photorefractive centres. An analysis of the amplitude of the overall shared grating has shown that with increasing readout beam intensity the holographic grating thickness decreases. In this case, under negative feedback the grating amplitude decreases, while with positive feedback it increases. The possibility is shown of achieving (under positive feedback) a maximum value of diffraction efficiency and complete energy transfer in a finite thickness of the photorefractive crystal, in contrast to the infinite thickness required in the standard two-beam coupling case.

Controlled, Periodic Domain Formation in Strontium Barium Niobate Induced by Volume Holograms

We demonstrate an all-optical technique of controlled, periodic ferroelectric domain reversal induced by electronic space charge fields associated with photorefractive volume holograms. This technique may be used to selectively fix and update individual holograms in photorefractive crystals.

Spatial frequency mixing in lithium niobate

The utilization of frequency difference holograms has been proposed for nondestructive read-out of dynamic holograms in photorefractive crystals. We identify the main mechanism responsible for the nonlinear spatial frequency mixing. Good agreement between experimental data and theory is obtained.

Two-level model of recording and reading of volume phase holograms in photorefractive crystals of BSO-type

A two-level model of optical transitions in crystals of BSO-type has been proposed for the effect of readout beam on the dynamic holographic grating to be taken into account, and an expression for diffraction efficiency representing the generalized formula by Vinetskii and coworkers [1–3] has been obtained.

Adaptive fringe-locked running hologram in photorefractive crystals: errata

Get PDF Email Share Share with Facebook Tweet This Post on reddit Share with LinkedIn Add to CiteULike Add to Mendeley Add to BibSonomy Get Citation Copy Citation Text Jaime Frejlich, Paulo Magno Garcia, and Lucila Cescato, "Adaptive fringe-locked running hologram in photorefractive crystals: errata," Opt. Lett. 15, 1247-1247 (1990) Export Citation BibTex Endnote (RIS) HTML Plain Text Citation alert Save article

Fringe-locked running hologram and multiple photoactive species in Bi12TiO20

Fringe-locking techniques ar used for the recording of stable 90 ° phase-shifted running holograms in photorefractive crystals. The use of this technique permits the characterization of a fast and a slow photoactive species in Bi12TiO20. We compare our results with those obtained from other methods and discuss the practical interest of this technique.

Adaptive fringe-locked running hologram in photorefractive crystals

We have recorded running holograms in a photorefractive crystal with an applied electric field, using a 90 degrees phase-shift fringe-locked interference pattern of light. This method provides a simple way to obtain optimal conditions for nonstationary holographic recording. The experiment that we describe allows us to calculate the crystal diffusion length L(D) and provides direct evidence of the occurrence of running holograms in photorefractive crystals. Experimental results for a Bi(12)SiO(20) sample are reported.

Adaptive Holographic Interferometers Operating Through Self-Diffraction Of Recording Beams In Photorefractive Crystals

This paper gives a comparative analysis of different techniques of continuous readout of volume holograms in photorefractive crystals. The techniques rely on self-diffraction of recording beams and can be used as a basis for developing adaptive holographic interferometers that ensure a high degree of reliability of interferogram formation. The use of adaptive interferometers for the analysis of vibrations and displacements of real objects is illustrated using the photorefractive Bi12Ti020 crystal. This crystal exhibits the highest holographic sensitivity among presently known photorefractive crystals for recording by cw lasers in the red region of the spectrum. The applicability of photorefractive crystals for conversion of phase variations of recording light beams into intensity variations is considered. This enhances the sensitivity of interferometers to vibrations to be measured. The experimental measurements of vibration amplitudes as low as 1 A using Bi12Ti020 and a 0.63 µm laser are reported.

Use of microcomputers in theoretical physics courses: three examples

When teaching physics nowadays, personal computers (PCS) offer a powerful tool to acquaint students with realistic systems and models of theoretical physics. The authors give three examples: fractals, holograms in photorefractive crystals and transport in disordered systems.