Imaging birefringence at sub-micrometre resolution has demonstrated its potential as a powerful label-free method to get insight into the structure of biological tissues, both for fundamental research and for biomedical applications. However, achieving sensitive birefringence imaging in real-time is a challenge. Recently our laboratory has successfully demonstrated real-time Mueller laser-scanning microscopy based on the idea of spectrally encoded light polarization. This method implements a very fast swept-wavelength laser source in combination with passive polarization optics, enabling high-speed polarization modulation (<MHz) and thus fast polarization measurements. However, as a Jones/Mueller method, it is operating off null (far from extinction) so its sensitivity is intrinsically limited. Here, we report a new version of the spectrally encoded light polarization microscope dedicated to weak linear retardance measurements and combining the high sensitivity of a null method with the speed of the spectrally encoded light polarization method. We expect that the superior performances of this new device will open the gate for real-time imaging of very weak birefringent structures within biological samples.
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