Polarization metrology based on the conical refraction phenomenon

A. PEINADO; A. TURPÍN; A. LIZANA; E. FERNÁNDEZ; C. IEMMI; J. MOMPART; J. CAMPOS

Santiago de Compostela

Congreso; ICO 23; 2014

International Comission for Optics

Polarization information is useful in a large number of applications, such in astronomy for studying the physical processes occurring in our solar system[1], in medicine for the diagnosis of cancer[2], in industry for material characterization[3], among others. We can classify polarimeters in several categories[4]: Stokes or Mueller polarimeters depending if we are characterizing the polarization of a light beam or the polarimetric properties of a sample; punctual or imaging polarimeters; complete or incomplete polarimeters depending if we can characterize all the polarization parameters; spectro-polarimeters if we are using a range of wavelengths; time-sequential or instantaneous polarimeters depending on the duration of the measurement. Each architecture has particular advantages and limitations compared to the others. Thus, depending on the application, a specific architecture will be selected to fulfill the measurement requirements.In this work, we present a new methodology for determining the polarization of a light beam based on the conical refraction (CR)[5]. CR phenomenon[6?8] occurs when we illuminate a biaxial crystal along one of its optical axes. Then, the beam is transformed to a ring of intensity, sharply resolved at the Lloyd plane. The polarization distribution along this ring is mapped in Fig.1(a). Each point is linearly polarized and its azimuth rotates along the ring. The intensity distribution of this ring depends on the State of Polarization (SoP) of the incident beam. On one hand, when we illuminate with unpolarized light or circularly polarized light, we observe the whole ring with uniform intensity (Fig.1(a)). On the other hand, when we illuminate with linearly polarized light we observe a non uniform bright ring, with maximum of intensity where the polarization of the ring has the same orientation as the incident SOP and a null of intensity where the polarization of the ring is orthogonal to the incident azimuth (Fig.1(b)). Therefore, the biaxial crystal projects the incident beam over a set of linearly polarized states from 0º to 180º. This is the fundamental physical property on which our polarimeter is based.