Dynamic ultrasound modulated optical tomography by self-referenced photorefractive holography

Abstract

Photorefractive Bi(12)SiO(20) single crystal is used for acousto-optic imaging in thick scattering media in the green part of the spectrum, in an adaptive speckle correlation configuration. Light fields at the output of the scattering sample exhibit typical speckle grains of 1 μm size within the volume of the nonlinear crystal. This heterogeneous illumination induces a complex refractive index structure without applying a reference beam on the crystal, leading to a self-referenced diffraction correlation scheme. We demonstrate that this simple and robust configuration is able to perform axially resolved ultrasound modulated optical tomography of thick scattering media with an improved optical etendue.

Real-time suppression of turbidity of biological tissues in motion by three-wave mixing phase-conjugation

“…reconstruction by computation from diffused waves [2], time gating to isolate the less diffused photons [3], acousto-optic methods [4,5,6] and imaging by two-photon absorbtion [7].…”

Modelization and optimized speckle detection scheme in photorefractive self-referenced acousto-optic imaging

“…When the US transducer is now operating over short pulse duration the incident speckle structure is changed and it diffracts a wavefront which does not perfectly match with the complex phase hologram recorded in the volume of the BSO. In such conditions the diffracted intensity on the detector is reduced or enhanced as shown in [12] and permits an acousto-optic imaging of a phantom embedded in the scattering medium. It was also shown experimentally in [12] that in the case of self referenced holographic configuration an optimum signal detection is obtained when the two following conditions are fulfilled: first, the speckle grain size recorded in the PR crystal must be of the order of the Debye screening length.…”

“…In such conditions the diffracted intensity on the detector is reduced or enhanced as shown in [12] and permits an acousto-optic imaging of a phantom embedded in the scattering medium. It was also shown experimentally in [12] that in the case of self referenced holographic configuration an optimum signal detection is obtained when the two following conditions are fulfilled: first, the speckle grain size recorded in the PR crystal must be of the order of the Debye screening length. Second, the position of the detector in the transverse plane must be optimized due to the spatial frequency response of the photorefractive effect when speckle is involved.…”

“…This type of interaction was demonstrated by Kamshilin et al [11] for application of PR correlation filtering to the detection of vibrating rough surfaces or vibrating multimode fibers. The proof of principle for AO imaging is illustrated by Benoità la Guillaume et al [12] with a dynamic 2D image of ink inclusions embedded within 40mm of a multiply scattering phantom. The PR crystal used is the sillenite type Bi 12 SiO 20 (BSO), known for its high photosensitivity in conventional holographic experiments in the blue-green spectral region.…”

“…The experimental setup detailed in Ref. [12] is shown in when the US transducer is off, the incident speckle field is perfectly phase matched with the recorded phase volume hologram. It thus results an optimum coherent diffraction on the detector.…”