Spatial and temporal characteristics of electrically fixed holograms in photorefractive strontium-barium niobate

We report measurements of the holographic diffraction efficiency (HDE) of single photorefractive gratings fixed by an externally applied voltage pulse in Sr0.75Ba0.25Nb2O6. The polarization grating HDE and decay rate are strongly dependent on the grating spacing and also depend on the intensity of the light beams during the recording and erasing/reconstruction process. Knowledge of the dependence of the fixing process on spatial frequency may be useful for the creation of physical models of local polarization switching in ferroelectrics

Order-of-magnitude reduction of the photorefractive response time in rhodium-doped Sr0.6Ba0.4Nb2O6 with a dc electric field

We present what is to our knowledge the first report on the photorefractive properties of Rh-doped Sr0.6Ba0.4Nb2O6 and experimental results showing a reduction of the photorefractive two-beam coupling response time by more than an order of magnitude with an external dc field of 10 kV/cm

Photorefractive gain and response time of Cr-doped strontium barium niobate

We present experimental results on the photorefractive two-beam coupling constant and response time of two Cr-doped strontium barium niobate crystals with different dopant concentrations. Both showed significantly faster response times over Ce-doped SBN:60, but with corresponding decreases in their coupling constants

Light-induced absorption in photorefractive strontium barium niobate

Sr0.59Bao.41Nb2O6 and Sro.75Bao.25Nb2O6 exhibit an intensity-dependent absorption in the visible spectral range. We perform pump (green)-probe (red) measurements and find variation as high as 0.45 cm-' in the absorption coefficient, which depends significantly on the polarization of the probe light beam. Our results indicate a nonexponential dark decay time of the induced absorption and suggest that the trapping potential of the shallow traps varies significantly from one trap to another (multiple isolated shallow traps)

Electrical fixing of photorefractive holograms in Sr0.75Ba0.25Nb2O6

Photorefractive holograms stored in Sr0.75Ba0.25Nb2O6 crystals are electrically fixed at room temperature. The fixed holograms can be read out directly or after a positive-voltage pulse is applied that can dramatically enhance the diffraction efficiency. Single gratings as well as images are recorded and fixed

Electric-field multiplexing/demultiplexing of volume holograms in photorefractive media

We propose a new method of volume hologram multiplexing/demultiplexing in noncentrosymmetric media. Volume holograms may be multiplexed by tuning the material parameters of the recording medium (such as refractive index or lattice parameters) while keeping the external parameters (wavelength and angles) fixed. For example, an external dc electric field alters the index of refraction through the electro-optic effect, effectively changing the recording and reconstruction wavelengths in the storage medium. Then the storage of holograms at different fields, hence different indices of refraction, is closely related to wavelength multiplexing. We demonstrate this concept in a preliminary experiment by electrically multiplexing two volume holograms in a strontium barium niobate crystal

Self-starting passive phase conjugate mirror with Ce-doped strontium barium niobate

We report the use of Ce-doped SrxBa1−xNb2O6, x=0.60 and 0.75, as the holographic four-wave mixing medium in the construction of a self-starting passive phase conjugate mirror using internal reflection. Without correcting for Fresnel reflections, a steady-state phase conjugate reflectivity of 25% was measured with Sr0.75Ba0.25Nb2O6:Ce. The distortion correcting property of such a mirror was demonstrated using an imaging experiment

Photorefractive properties of Ce- and Ca-doped Sr0.6Ba0.4Nb2O6

We present the results of experimental study of the absorption coefficient, two-beam photorefractive coupling constant, and photorefractive response time of a doubly Ce- and Ca-doped Sr0.6Ba0.4Nb2O6. This crystal displays enhanced photorefractive response at near infrared wavelengths when compared to Ce-doped SBN:60. The temperature dependence of the coupling constant over the range from –30 to 40 °C has also been studied

Phase-locked sustainment of photorefractive holograms using phase conjugation

A method for sustaining multiply exposed photorefractive holograms, in a phase-locked fashion, by using a pair of phase-conjugating mirrors is described. It is shown that a steady state exists where the overall diffraction efficiency is independent of the number of holographic exposures and the final holograms are exactly in phase with the initial ones. Both analytical and experimental results are presented

Optical and electrical Barkhausen noise induced by recording ferroelectric domain holograms

Ferroelectric domain gratings with periods of the order of an optical wavelength are induced in strontium barium niobate by photorefractive space-charge fields. We measure the Barkhausen noise in current and diffraction efficiency while optically recording domain gratings and show that the two are strongly correlated in time. Significant random depolarization occurs under high-intensity illumination. We deduce the kinetics of the domain inversion process from the shape of the current transients