Institut Fresnel

Quantitative phase microscopy for Biology

keywords : lateral shearing interferometry, phase contrast, wavefront sensing, microscopy

Quantitative phase imaging techniques are now conventionally used in microscopy for measuring specific properties of semi-transparent samples without any labelling. By placing a wavefront sensor on the exit image plane of a microscope, we measure the complex field spatial distribution in this plane, and then retrieve the quantitative optical path difference (OPD) of the observed sample. Most of works presented in this page were developed in a close collaboration with a company (Phasics SA, Saint-Aubin, France).

The wavefront sensor we use is a commercial Quadri-Wave Lateral Shearing Interferometer (QWLSI) provided by Phasics SA. It is an efficient tool for measuring phase gradients of optical beams along two perpendicular directions. Post-processing integration then allows obtaining the complete phase spatial distribution of the beam with a high spatial resolution (diffraction-limited). Moreover, QWLSI is achromatic, and thus compatible with the white-light illumination pathway of conventional wide-field microscopes.

In the last years, we extended the technique to new applications, where different physical phenomena produced a given sample-induced change in the phase of the exit optical beam that modulates the incident wavefront. More precisely, we used direct refractive-induced OPD, thermal-induced OPD, and resonant vibrational-induced OPD to produce phase contrast images of physical or biological samples, temperature distribution of complex patterns of nanostructures, and Raman spectra of polystyrene beads, respectively. We are now developing the technique to reach 3D resolution, but also to focus on optical retardance distribution inside observed samples.

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