Internship : Holographic Optical Coherence Tomography Combining Diffraction Grating and Wavelength-Scanning Source for Imaging in Scattering Tissues.

Objective: To achieve deep optical coherence tomography in scattering tissues by combining modulated laser and a diffraction grating with holographic detection on a camera. A linear illumination and slit detection will ensure optimal spatial confocal filtering. Approach: A linear pattern illumination generated by a scanning laser or a SLD, in the wavelength range of 820 nm to 870 nm, will be formed to illuminate a tissue sample, similar to the approach proposed by Arnaud Dubois [1]. The backscattered light will be spatially filtered by a slit and diffracted by a diffraction grating, to create a diffraction pattern that will be angularly scanned according to the wavelength variation of the laser. Alternatively, modulations of SLD light via current variation or via an optical switch will be investigated. This pattern will be recorded by an ultra-fast camera. The recording process will be done with an optical interferometer, by digital holography [2], to allow for high-sensitivity phase measurement under low-light conditions, thanks to the sampling of the beat at the frequency of modulation. The digital signal processing of the recorded optical field diffraction patterns will enable the selection of deep retro-scattered photons, and the filtering of coherent crosstalk that emerges from random optical path lengths in the scattering sample.