Some polarization properties of volume holograms in Bi(12)SiO(20) crystals and applications

Phase-compensated holographic recording based on anisotropic photorefractive diffraction

We report a simple actively stabilized setup for holographic recording on sillenite photorefractive crystals that is based on the anisotropic diffraction properties of these materials. The method is much simpler than previously published ones, requires neither phase modulation nor synchronous phase-sensitive detection, and needs no external reference. We describe the successful operation of this stabilization procedure for a Bi(12)TiO(20) crystal in a practical holographic interferometry setup, using the 632.8-nm wavelength of a He-Ne laser.

Optical phase conjugation in a magnetic photorefractive semiconductor CdMnTe

Magneto-optical phase conjugation was performed in a diluted magnetic photorefractive semiconductor crystal CdMnTe under an applied magnetic field. The magnetic field removes time-reversal symmetry and quenches orthogonal components of the phase-conjugate signal for selected field strengths. The experimental results as functions of magnetic field and incident polarization angle are in good agreement with coupled-mode theory with transmission gratings during magneto-photorefractive mixing.

Biological photochrome bacteriorhodopsin and its genetic variant Asp96 ? Asn as media for optical pattern recognition

The biological photochrome bacteriorhodopsin (BR) is contained within the purple membrane (PM) of Halobacterium halobium. Artificial derivatives with improved optical properties can be generated by genetic methods and isolated from mutated halobacterial strains. The use of PM films that contain wild-type BR and BR variants as real-time recording media for various holographic applications has been reported previously, and the advantages of BR variants have been demonstrated. The high reversibility (>> 10(5) record/erase cycles), the fast time scale of its photoconversions (femtoseconds to milliseconds), and the large photochromic shift ( approximately 160 nm) occurring during its photocycle make it a promising material for real-time applications. A dual-axis joint-Fourier-transform (DA-JFT) correlator is used to demonstrate the applicability of PM films in holographic pattern recognition. One major advantage of PM films in this application is their high spatial resolution of more than 5000 lines/mm. Severe restrictions on the overall performance of the DA-JFT correlator system are caused by scattered light and result in a low signal-to-noise ratio. Since PM patches typically have a diameter in the range of the visible wavelengthsthat are used for hologram recording, light scattering is an intrinsic problem of PM films. The polarization recording properties of PM films are employed to overcome this problem. More than 20-fold improvement of the signal-to-noise ratio in the DA-JFT correlator output is obtained.

Spatial light modulation by beam coupling in GaAs crystals

We present the first reported demonstration of spatial light modulation in GaAs using the photorefractive effect. The demonstration was done with a special configuration in which polarization rotation created by beam coupling was utilized.

Real-time enhancement of defects in a periodic mask using photorefractive Bi(12)SiO(20)

The first known experimental results of real-time optical defect enhancement of a periodic mask are reported. A low-intensity reference wave interferes with the Fourier transform of an object beam to form a hologram in a photorefractive crystal. The nonlinear properties of the crystal perform a filtering operation, and phase-conjugate readout results in a defect-enhanced image. Defects of size 10 microm x 100 microm have been easily detected with high signalto- noise ratio, and a discussion of performance limitations is presented.

Holographic recording and reconstruction of polarized light with dyed plastic

Recording and reconstruction of the polarization state of the object beam is achieved by using dyed red plastic as a holographic material. Holographic characteristics are presented of dyed red plastic involving beam powers ranging between 3 and 120 mW/cm2 and exposure times in the order of minutes. It is also shown that the resulting modulation becomes photostationary under continuous exposure.