Liquid Crystal Retarders for fully automated fast measurement of the Mueller Matrix of the skin without moving parts

Depolarization or rotation of polarisation of light upon scattering in tissue depends on the tissue type and may have significant diagnostic power. One way to determine the polarization properties of a sample is to measure the Mueller Matrix (MM). With this MM ((M_m ) ⃗), it is possible to calculate the Stokes vector ((S_o ) ⃗) of the scattered light, which contains all polarization information, for every Stokes vector ((S_i ) ⃗) of the illuminating light by using the equation S ⃗_o= M ⃗_m∙S ⃗_i. To measure the spatially resolved MM of skin, it is necessary to take pictures with different polarization states of the illuminating and the observed light. Additionally, for measuring the MM in vivo, it is necessary to measure it in a short time to reduce motion artefacts, for example. In our new setup, we achieve full polarization control and fast change between polarization states by using liquid crystal retarders. The system makes it possible to measure the MM of the skin and investigate its diagnostic advantages compared to standard approaches. In the future, such a setup could be part of a dermatoscopic device to provide extra information for the physician.