Degenerate four-wave mixing in KNbO(3): picosecond and photorefractive nanosecond response.

Single 75-ps-long pulses at a wavelength of 532 nm are used to write phase gratings in KNbO(3) crystals. Two grating buildup processes are resolved. The faster and generally weaker one is instantaneous on a time scale of the pulses used and is attributed to intrinsic third-order processes. In a reduced crystal that shows preferentially electronic charge transport and that is oriented to show a space-charge-induced photorefractive effect, a higher diffraction builds up in some nanoseconds after the illumination of the crystal. The rise time of the photorefractive grating does not seem to depend on the grating period. Two tentative explanations are proposed: (i) a high electron mobility and a limited response time owing to ferroelectric relaxation processes and (ii) fast electron recombination.

[1]  M. Soskin,et al.  Holographic storage in electrooptic crystals. i. steady state , 1978 .

[2]  M. Z. Zha,et al.  Reduced KNbO3-crystals for fast photorefractive nonlinear optics , 1987, Topical Meeting on Photorefractive Materials, Effects, and Devices.

[3]  Arthur L. Smirl,et al.  Formation, decay, and erasure of photorefractive gratings written in barium titanate by picosecond pulses , 1989 .

[4]  G Roosen,et al.  Time-resolved buildup of a photorefractive grating induced in Bi(12)SiO(20) by picosecond light pulses. , 1988, Optics letters.

[5]  J. Feinberg,et al.  Photorefractive-index gratings formed by nanosecond optical pulses in BaTiO(3). , 1981, Optics letters.

[6]  Peter Günter,et al.  Optimization of the photorefractive properties of KNbO3 crystals , 1988 .

[7]  P. Günter,et al.  Photorefractive effects and photocurrents in KNbO3: Fe , 1978 .

[8]  Ivan Biaggio,et al.  BUILD-UP AND DARK DECAY OF TRANSIENT PHOTOREFRACTIVE GRATINGS IN REDUCED KNbO3 , 1990 .

[9]  Sokoloff,et al.  Direct observation of relaxation modes in KNbO3 and BaTiO3 using inelastic light scattering. , 1988, Physical review. B, Condensed matter.

[10]  M. Fontana,et al.  The intrinsic central peak at the structural phase transitions in KNbO3 , 1988 .

[11]  A M Glass,et al.  Fundamental limit of the speed of photorefractive effect and its impact on device applications and material research: comment. , 1987, Applied optics.

[12]  Time resolved investigation of transient photorefractive gratings in KNbO3 , 1990 .

[13]  J. Gazengel,et al.  Picosecond holography and four-wave mixing in BSO , 1986 .