Photorefractive correlation filtering of time-varying laser speckles for vibration monitoring

Abstract

We proposed and experimentally studied a technique of vibration object monitoring. The technique is based on self-diffraction of the speckle pattern on the adaptive correlation filter recorded in photorefractive Bi12TiO20 crystal. This filter is recorded owing to the light-induced scattering known as fanning effect. The proposed technique is as sensitive as interferometric systems and it is very simple for implementation: neither reference nor readout beam is needed for operation. It is shown that the system has a linear response on the lateral displacement of the object surface and its dynamic range can be easily varied depending on experimental conditions.

Contribution of the inverse flexoelectric effect to counterpropagating two-wave mixing of light beams in photorefractive crystals

“…1) in a photorefractive crystal causes a dynamic hologram to form in it, on which they are simultaneously selfdiffracted. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17]19 This involves the interference of each of the transmitted beams with one of the diffracted beams-i.e., reference beam I P interferes with I S1 , and I S interferes with I P1 . The output intensity of the signal beam transmitted through the crystal is expressed as…”

“…[1][2][3] The dynamic character of three-dimensional phase holograms in photorefractive crystals makes it possible, for example, when there is two-wave mixing on such crystals, to carry out adaptive correlation filtering of the speckle patterns of the light field in precision optical sensors. [4][5][6][7] In a traditional layout with copropagating mixing of two beams, in order to increase its diffraction efficiency, the resulting transmission hologram requires an external electric field of 10 kV∕cm or more to be applied to cubic crystals, which have small electro-optic coefficients. [1][2][3][4][5][6][7] This makes a measurement system based on transmission-type photorefractive holograms complicated, costly, and energy-intensive.…”

“…[4][5][6][7] In a traditional layout with copropagating mixing of two beams, in order to increase its diffraction efficiency, the resulting transmission hologram requires an external electric field of 10 kV∕cm or more to be applied to cubic crystals, which have small electro-optic coefficients. [1][2][3][4][5][6][7] This makes a measurement system based on transmission-type photorefractive holograms complicated, costly, and energy-intensive. Moreover, there are a number of applications in which it is unacceptable to use high voltages.…”

“…[8][9][10][11][12][13][14][15] One possible application of volume holograms in photorefractive crystals is a laser interferometer. [1][2][3][4][5][6][7]11,[14][15][16][17] Laser interferometers convert phase modulation of light into intensity modulation, and this allows the mechanical vibrations of surfaces that reflect or scatter the light beams to be measured with high accuracy. The maximum sensitivity of a classical interferometer to the amplitude of the vibrations being measured is limited by the shot noise of the photodetector and is estimated in Ref.…”

Light-Induced Scattering and Energy Transfer between Orthogonally-Polarized Waves

“…Therefore, eliminating or at least suppressing the effect of holographic scattering becomes a main goal in order to promote photorefractive crystals for industrial applications [1]. On the other hand, holographic scattering has been advantageously utilized for a wide variety of applications such as optical limiters [2,3], color or coherent--to-incoherent converters [4,5], novelty filters [6,7], vibration object monitoring [8], logic operations [9,10], hologram multiplexing techniques that use random wave generated by beam fanning instead of external diffusers [11] and material characterization [12][13][14][15][16].…”