Biaxial crystal as a versatile mode converter

The extreme versatility of the internal conical refraction in biaxial crystals in the transformation of Gaussian laser beams is demonstrated and discussed. By means of simple variations in the focusing and polarization of the input beam, various beam configurations like Bessel–Gauss, Hermite–Gauss, Laguerre–Gauss, and others are shown to be produced from a lowest-order Gaussian beam passed through a biaxial crystal along one of its optical axes. Further transformations of the beam profile and formation of more complex light patterns were obtained in a cascaded scheme, when the beam was passed consecutively through two crystals. These observations, together with the known ability of conical refraction to form a variety of other complex light structures, demonstrate the unique properties of the effect in manipulations with the amplitude, phase, and polarization of light beams.