Swept-wavelength null polarimeter for high-speed weak anisotropy measurements

Null-polarimeters provide the best sensitivity to anisotropy measurements and so far have been developed for the detection of small optical activities. This paper revisits null polarimetry through an original configuration based on the concept of spectrally encoded light polarization, in order to measure, with unprecedented speed, either linear or circular retardance with the same degree of sensitivity . Using passive polarization optics and a high speed wavelength swept laser source, the achieved single-pass sensitivity was 55nrad/Hz and 45nrad/Hz for respectively linear and circular retardance considering a minimum acquisition time of 10 µs. Due to its compactness and rapidity, the method could be further implemented in laser scanning microscopes, which should be of great interest for revealing very low anisotropies in biological tissues.