Adaptive correlation filters for speckle patterns in photorefractive crystals

Spectral dependence of absorption photoinduced in a Bi12TiO20crystal by 532-nm laser pulses

“…can noticeably expand the spectral range of this crystal as a dynamic medium, thereby expanding applications of holographic devices based on photorefractive BTO crystals. Another important parameter of photosensitive media for dynamic holography devices is their response time [2,24,25]. The minimal possible formation time of dynamic holograms in photorefractive crystals is equal to the Maxwell relaxation time t M [2].…”

“…In accordance with the model of photoinduced impurity absorption presented above, this is caused by the population of traps with average ionisation energies E 1 1X60 eV and E 2 2X57 eV by photoexcited electrons and should increase both the speed of response and the eféciency of dynamic holography devices based on photosensitive BTO crystals. Note here that irradiation of crystals in such devices by radiation from semiconductor light-emitting diodes (for example, in adaptive correlation élters [24,26] and adaptive holographic interferometers [27]) can be readily performed.…”

Continuous monitoring of a surface slope by real-time shearing interferometry with a photorefractive crystal

“…This movement in the stationary index grating induces polarization changes and energy redistribution among the beams. 21,22 This produces signal variations on the photodiode, which corrupts the desired out-of-plane signal. Because of the fringe modulation along the x axis, an in-plane displacement along this axis produces much larger changes than along the y direction.…”

“…This parasitic signal is low because, conversely to the system described in Ref. 22, we detect the whole beam, thus integrating the signal over a large number of speckle dots. With the inplane displacement producing a signal inversely proportional to the transverse magnification ␥, we expect this parasitic signal to be fully negligible for systems with smaller transverse magnifications, i.e., with systems optimized for observing large areas.…”