Conical Diffraction Holography and Two-Wave Mixing

Conventional holograms record the intensity of an interference pattern and are therefore usually written using an object and a reference wave sharing a common light polarization, thus maximizing the fringe contrast. Exceptions to this rule exist in the framework of polarization holography [1], which permits to store the polarization state of a wave using polarization-sensitive media. This approach can be used for instance to generate vector beams [2] which have non-uniform polarization distribution. A specific type of vector beams can be created naturally via the conical diffraction (also known as conical refraction) effect occurring upon propagation of a focused beam along one of the optic axes of an optically biaxial crystal [3]. Even for a homogeneously polarized input wave, conical diffraction (CD) gives rise to a double circular ring where different linear polarization are spread azimuthally across the ring [3]. Here we combine for the first time this linear optical effect with the nonlinear recording of dynamic holograms in a photorefractive (PR) material, with all processes taking place within the same medium. Even though the hologram recording is driven by the intensity distribution as in conventional holography, we show that efficient recording can be achieved with any combination of the input polarizations of the object and reference waves, including the case of orthogonal linear or circular polarizations.