This activity has emerged in 2006 with the funding of the project by the ANR (Aspect-Peau Project). In the frame of this project we develop a spectroscopic OCT system with inherent capacity of real time investigation of spectrally resolved A-scan. Compared to the current state of the art in spectroscopic OCT our system present several specificities : no correlation scanning is necessary (contrary to time domain OCT) and no numerical processing is involved to access the spectroscopic information as the signal processing is optically realized. Our first application, after acquisition optimization of our system, will be to develop a probe for early skin cancer detection. This probe must fulfill several conditions: to be able to efficiently distinguish between cancerous or normal tissues, to access simultaneously to the depth extension of the detected lesion, to be at an affordable price in order to be highly spread over patricians (dermatologist).
Parameters playing a key role for sensitivity are : Average Power of the source, detector SNR, dynamic and sensitivity, the detection modality (heterodyne or not), residual dispersion (sample induced dispersion. All these parameters dramatically decreases both SNR and resolution of the whole system. We have just published an article on the system we are developping. This peer reviewed journal (International Journal of Biomedical Imaging) is a new one published since 2006 by Hindawi Publishing group. The access is free for everybody (like Optics Express).
The principle could be quite intuitively explained through optical correlation which is realized when two ‘temporally’ correlated white light beams are incident with a certain angle one to the other on a detector. This results in a temporal amplitude correlation operation strictly comparable to what is obtained in the Young slit experiment with white light illumination. The correlation is realized with no moving element only depending on the angle between beams. The difference is here that the diffraction grating realized an under sampling of the white light interference pattern what leads to the need of a lower pixel number on the detector to resolve the full correlation signal. If a dispersive prism P is inserted in the correlation system, with a dispersion direction crossed with respect to the grating diffraction plane, then the correlation will be demultiplexed over the spectral channels of the dispersive prism. In the plane of the detector D we then have directly the absorption resolved in depth.
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