In situ monitoring of the photorefractive response time in a self-adaptive wavefront holography setup developed for acousto-optic imaging

Max Lesaffre (1) , F. Jean (1) , François Ramaz (1) , Albert-Claude Boccara (1) , Michel Gross (2) , Philippe Delaye (3) , Gérald Roosen (3)

1 IL - Institut Langevin - Ondes et Images (UMR7587)
2 LKB (Lhomond) - Laboratoire Kastler Brossel
3 Laboratoire Charles Fabry de l'Institut d'Optique / Manolia

The measurement of optical contrasts within thick biological tissues can be performed with the hybrid technique of acousto-optic imaging, but it has been shown that an acquisition rate in the 1−10kHz range is required for a good efficiency. This comes from the interferometric nature of the signal, blurred by speckle decorrelation in a time c, due to a decrease of the speckle pattern contrast at the exit of the sample. An holographic setup that associates a fast and large area single photodetector and a photorefractive crystal, can measure in real-time the acousto-optic signal: this is the so-called self-adaptive wavefront holography technique. Nevertheless, it is essential to size the photorefractive response time (PR) of the crystal with c in order to optimize the signal-to-noise ratio of the measurement. This time mainly depends on the overall light intensity within the crystal. We have developed an original in situ method to determine PR with the combination of acoustic pulses and a frequency de-tuning of the reference beam. We can measure precisely this time but also monitor it according to a theoretical model that we have previously described. We are able to adapt the response time of the setup to the decorrelation time of the medium under study

Domains: Optics [physics.optics]

Max Lesaffre, F. Jean, François Ramaz, Albert-Claude Boccara, Michel Gross, et al.. In situ monitoring of the photorefractive response time in a self-adaptive wavefront holography setup developed for acousto-optic imaging. Optics Express, 2007, 15 (3), pp.1030-1042. ⟨hal-00671108⟩