Novel observations in internal conical diffraction

Abstract

Internal conical diffraction occurs when a beam of light is incident along an optic axis direction in a biaxial material. The beam transforms into a hollow skewed cone inside the material and refracts upon exiting. The phenomenon has been studied extensively for the case of laser beams with Gaussian spatial intensity profiles incident along an optic axis of a biaxial crystal. When a top-hat incident beam is used, the resultant intensity profile beyond the crystal is observed to be distinct from that generated using a Gaussian beam. The evolution of a conically diffracted top-hat beam has many intensity oscillations along its centre, and these can be observed with a suitable experimental apparatus. Dispersion in biaxial crystals results in a complex beam structure when using a broadband light source. A transition between conical diffraction and double refraction is observed over the full spectrum of the incident beam. The theoretical model describing this transition may be expanded to contain an explicit wavelength dependency. Simulations of the intensity profile may be produced which match experimental observations closely. Dispersion compensation may be realised in biaxial crystals using a suitable experimental arrangement, resulting in a white ring of light at the focal image plane.