Abstract
Several approaches exist to perform acousto-optic imaging of multiple-scattering media such as biological samples. Up to now, most of the coherent detection methods use holographic setup based on photorefractive crystals such as BSO or SPS. One of the issue of these techniques is the moderate response time compared to the speckle decorrelation time in biological sample. We introduce a new approach for the holographic detection based on two-wave mixing in a Nd:YVO4 gain medium enabling us to perform a fast wavefront adaption (50 μs) of the speckle field from a multiple-scattering sample.
Highlights
Tagging photons with ultrasound is an attractive method to image the optical properties inside multiple-scattering media such as biological tissues [1]
As outlined in the article, adaptive wavefront holography is a fast process in gain media such as Nd:YVO4
The response time is a main advantage for ultrasound optical tomography imaging of biological tissues due to the problems of speckle decorrelation that arises when performing in vivo experiments
Summary
Tagging photons with ultrasound is an attractive method to image the optical properties inside multiple-scattering media such as biological tissues [1]. The coherent methods, on the other hand, are based on the idea of phasing each speckle grain of one component (tagged or untagged) of the speckle field in order to increase the SNR This can be performed by creating a new wavefront that is matched with, for example, the wavefront of the untagged photons. One of the issue that can come up with in vivo experiments is that the speckle has a decorrelation time constant of about 1 ms [8, 9] in biological tissues, while the required time to write the hologram inside a photorefractive crystal is usually between a few ms to 100 ms [6, 7] To overcome this problem, we propose in this article a new approach of TWM based on a gain media (Nd:YVO4). The first experimental results of imaging a scattering phantom with 3 black inclusions will be presented before discussing the outcomes and the perspectives of the use of gain media for this imaging process
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