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

Dynamic electronic compensation of fixed gratings in photorefractive media

We present a model describing the formation of a photorefractive grating in the presence of photorefractively inactive space-charge modulation. The treatment is based on standard linearized Kukhtarevs equations. The model developed is applied to the interpretation of experimental results on electrical fixing in Sr0.75Ba0.25Nb2O6

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

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

Electrooptic and piezoelectric measurements in photorefractive barium titanate and strontium barium niobate

We have measured the low-frequency ( unclamped ) electrooptic and piezoelectric coefficients in undoped BaTiO3and SrxBa1-xNb2O6 (x = 0.61) crystals using interferometric techniques. The contribution of the piezoelectric effect to the Pockels measurements is discussed. For an applied ac electric field in the range 0.1-200 V/cm, the electrooptic and piezoelectric effects are linear in the magnitude of the applied field and independent of its frequency in the range 10 Hz-100 kHz. The unclamped electrooptic coefficients of poled BaTiO3 single crystals are r13= 19.5 pm ±1 pm/V and r33 = 97 pm ±7 pm/V, and for strontium barium niobate are r13 = 47 pm ± 5 pm/V and r33 = 235 pm ± 21 pm/V, all measured at a wavelength of 514.5 nm and at T = 23°C. For the barium titanate samples the measured Pockels coefficient rc ≡ r33 - (n1/n3)3 r13 = 79 pm 6 pm/V is in good agreement with the value rc = 76 pm 7 pm/V computed from the above values of r13 and r33, where n1 and n3 are the ordinary and extraordinary indexes of refraction, respectively. The measured piezoelectric coefficient is d23 = +28.7 pm ± 2 pm/V for barium titanate, and is d23 = +24.6 pm ± 2 pm/V for strontium barium niobate. We also measured the photorefractive coupling of two optical beams in the crystals, and we show that the dependence of the coupling strength on beam polarization is in fair agreement with the measured values of the Pockels coefficients