Unfolding conical diffraction in semi-cavities

Abstract We experimentally and theoretically investigate double-pass semi-cavities incorporating different types of retroreflectors and an optically biaxial crystal (BC). Our study focuses on the conical diffraction (CD) patterns that arise in these configurations and on their analysis by means of an unfolding procedure. The latter allow to reduce the complex light propagation in each semi-cavity to a sole forward propagation through a corresponding cascade of two properly oriented BCs. This approach enables a clear theoretical prediction of the vectorial CD patterns observed experimentally. We further analyze the impact of polarization filtering and of the insertion of a lens in the semi-cavity feedback loop, showing how these elements are modifying the resulting diffraction structures. The excellent agreement between theoretical model and experimental results highlights the robustness of our method in describing CD under feedback conditions. This work provides essential insights into the behavior of light in BC-based optical cavities and lays the foundation for studying more intricate cavity designs involving wave propagation along the optic axes of biaxial media.