Development of polarization-sensitive dual-comb spectroscopy for anisotropic materials

Dual-comb spectroscopy (DCS) is a modern method using two frequency combs with slightly different repetition rates [1,2]. The DCS down-converts a material response in the optical frequency domain to a rf signal that is easy to handle. It provides significant advantages over conventional spectroscopy such as high spectral resolution, broad spectral range, frequency precision, short measurement time, and so on. The DCS has mainly been applied to precise molecular gas spectroscopy [3]. There are several attempts to expand its application to solid state physics. One of the applications is the determination of complex refractive index of materials [4]. As changes in both the amplitude and phase inside the material can be measured by DCS, one can determine both the real and imaginary part of the refractive index without utilizing the Kramers-Kronig relation. In addition, we consider physically interesting materials such as low-dimensional nanostructures and polymers with polarization-dependent complex refractive index (optical anisotropy). For investigating their physical property, it is important to add polarization sensitiveness to the DCS. So far, we have developed a polarization-sensitive (PS) DCS using a rotating compensator polarimetry [5].