Non-contact fast Mueller matrix measurement system for investigation of bio-tissues

The orientation and concentration of structures like collagen within biological tissues can provide valuable information, for example, in skin disease diagnostics. Polarimetry lends itself for non-destructive investigation in various fields of research and development ranging from medical diagnostics to production monitoring, among others. We report on a system for polarimetric measurement of versatile targets in reflection and transmission mode. It efficiently determines the Mueller matrix (MM) of a sample under study and is also suited for in vivo applications. Generally, the Mueller matrix M_m allows to calculate the Stokes vector So of the light interacting with a sample, containing all information on its polarization properties, through S_o = M_m S_i where S_i is the Stokes vector of the illuminating light. The Mueller matrix can be derived from images taken with different polarization states of illuminating and observed light. In our setup we use liquid crystal retarders to precisely control the polarization states of the light. This enables fast measurement of the orientation of structures with high spatial resolution. In a first example, we demonstrate the capability of our system by characterizing electrospun fiber tissue implants and measuring the degree of alignment and orientation of the fibers in reflection mode. The results lead us to a deeper understanding of the signals which we expect from structures like collagen in skin. We were able to derive a correlation between the properties of the tissue structures, the parameters for production and the MM information, for the first time. This was possible by suitable decomposition of the MM into submatrices of known physical interpretation. In this work we present our latest results and discuss the next steps towards in vivo application in dermatology or tissue implant.