Shearing interferometry and structured illumination for the depth-resolved detection of fluorescent light

The strong scattering in biological tissue is one of the main challenges for optical methods for in-vivo diagnostics. Using fluorescent markers allows the suppression of scattered excitation light. This work presents a shearing microscope for the depth-resolved detection of fluorescent light. A combination of a structured illumination restricting the excitation volume on a coarse scale with a lateral shearing interferometer for the detection is used. The structured illumination is realized with a Sagnac interferometer coupled to a conventional fluorescence microscope. A Michelson interferometer with one of its mirrors tilted provides the lateral shear. This setup allows the reconstruction of the phase of the emitted wave fronts in spite of the short temporal coherence and the lack of spatial coherence. The depth information can be obtained from the curvature of the interferometrically reconstructed wave front. This poster shows first measurements at phantoms with scattering properties comparable to dental enamel proving the feasibility of the method.