Development of laser sources and interferometric approaches for polarization-based label-free microscopy

The project developed in this thesis describes the design and the experimental realization of optical methods which can probe the anisotropy of semitransparent media. The ability to manipulate polarized light enables a label-free imaging approach that can retrieve fundamental information about the sample structure without introducing any alteration within it. Such a potential is of great importance and methods like the ones based on polarization analysis are gaining more and more popularity in the biomedical and biophysical fields. Moreover, when they are coupled with fluorescence microscopy and nanoscopy, they may provide an invaluable tool for researchers. The optical method I developed mainly exploits the laser radiation emitted from tailored optical oscillators to dynamically generate polarization states. The realization of such states does not comprise any external active device. The resulting time-evolving polarization state once properly coupled to an optical system enables probing a sample to retrieve its anisotropies at a fast rate. The development of two different laser sources is presented together with the characterizations of their optical properties. One of them consists of a Helium-Neon laser modified by applying an external magnetic field to trigger the Zeeman effect in its active medium. The other one is a Dual-Comb source, that is a mode-locked (ML) laser generating a pair of mutually coherent twin beams. Moreover, the thesis delivers the theoretical model and the experimental realization of the optical method to probe the optical anisotropies of specimens. Finally, the technical realization of a custom laser scanning optical microscope and its imaging results obtained with such methods are reported.