Conical diffraction of a Gaussian beam with a two crystal cascade

C F Phelan,P R Eastham,J F Donegan,K E Ballantine,J G Lunney

doi:10.1364/oe.20.013201

Abstract

Internal conical diffraction by biaxial crystals with aligned optic axes, known as cascade conical diffraction is investigated. Formulae giving the intensity distributions for a cascade conically diffracted Gaussian beam are shown to compare well with experiment for the cases of two biaxial crystals with the same and different lengths and with the second crystal rotated with respect to the first. The effects of placing half wave-plates between crystals are also investigated.

Highlights

Internal conical refraction is a phenomenon of crystal optics in which a beam of light that is refracted into the optic axis of a biaxial crystal propagates as a cone of light in the crystal, and refracts into a hollow cylinder as it exits the crystal [1,2,3,4,5]
Several attempts have been made to extend the theory of conical refraction to deal with situations involving realistic light beams rather than idealized rays propagating in biaxial crystals
The propagation of paraxial light beams along the optic axes of successive biaxial crystals, known as cascade conical diffraction, has been receiving interest recently for the creation and annihilation of optical vortices [11], as a versatile beam shaping tool [12] and in connection with a novel type of laser based on conical diffraction [13]

Summary

Introduction

Internal conical refraction is a phenomenon of crystal optics in which a beam of light that is refracted into the optic axis of a biaxial crystal propagates as a cone of light in the crystal, and refracts into a hollow cylinder as it exits the crystal [1,2,3,4,5]. These predictions have been shown to agree well with theory for the case of the conically diffracted Gaussian beam [9,10]. The propagation of paraxial light beams along the optic axes of successive biaxial crystals, known as cascade conical diffraction, has been receiving interest recently for the creation and annihilation of optical vortices [11], as a versatile beam shaping tool [12] and in connection with a novel type of laser based on conical diffraction [13]. Berry has provided a paraxial theory for a general N-crystal cascade in which the relative orientation of crystals of differing lengths is considered [14]. Our results demonstrate that the paraxial theory provides an excellent account of the complex beams generated by crystal cascades

Background theory

Experiment compared with theory

Conclusion