Alex Sushkov Phys208 Oct Photorefractive effects and their applications
The effect Spatial variation of light intensity inside a photorefractive crystal Excitation of e - into the conduction band e - diffusion or drift Space-charge E-field n due to Pockels effect Photorefraction
The discovery
The materials LiNbO 3, LiTaO 3, BaTiO 3, KNbO 3, KH 2 PO 4, GaAs, …, organic and polymeric materials
Photorefraction – the easy way
Two-wave mixing
Four-wave mixing
Photorefraction+Cavity Photorefractive crystal as an amplifying medium Phase conjugation
Laser locking and phase conjugation
Holograms
Holographic data storage holograms in a single LiNbO 3 crystal have been demonstrated. Diffraction limit on storage capacity: n 3 V/ 3 10 Tb/cm 3.
Holographic data storage: I/O rates Access time: 100 s Readout rate: 1-10 Gbits/s Writing time: 10 seconds/hologram, 10Mbit/s
Holographic data manipulation
Holographic image recognition
Why do we still have CDs and laptops? High/low carrier mobility tradeoff: writing speed vs storage time (semiconductors/ferroelectrics). Beam fanning. Self-diffraction and other dynamic effects during hologram recording and reading. New materials being developed: photopolymers and photosensitive glasses.
References M. P. Petrov, S. I. Stepanov, and A. V. Homenko, Photorefractive Crystals in Coherent Optics, Nauka, St. Petersburg, H. M. Smith, Principles of Holography, Wiley, New York, G. S. He, S. H. Liu, Physics of Nonlinear Optics, World Scientific, Singapore, 1999.