Conical diffraction: observations and theory

Abstract

Conical refraction was produced by a transparent biaxial crystal of KGd(WO 4 ) 2 illuminated by a laser beam. The ring patterns at different distances from the crystal were magnified and projected onto a screen, giving rings whose diameter was 265 mm. Comparison with theory revealed all predicted geometrical and diffraction features: close to the crystal, there are two bright rings of internal conical refraction, separated by the Poggendorff dark ring; secondary diffraction rings decorate the inner bright ring; as the distance from the crystal increases, the inner bright ring condenses onto an axial spot surrounded by diffraction rings. The scales of these features were measured and agreed well with paraxial theory; this involves a single dimensionless parameter ρ 0 , defined as the radius of the rings emerging from the crystal divided by the width of the incident beam. The different features emerge clearly in the asymptotic limit ρ 0 ≫1; in these experiments, ρ 0 =60.

Conical refraction: fundamentals and applications

“…Although being the case of a Gaussian input beam the most studied situation in CR for cylindrically symmetric beams [33,[61][62][63][64][65][66][67][68][69], other works have investigated CR for Laguerre-Gauss beams [70,71] and for top-hat beams [72].…”

Conical diffraction and Bessel beam formation with a high optical quality biaxial crystal

“…It shows that the conically diffracted beam has a narrow double-ring profile in the focal image plane and then diffracts to yield a beam which has a maximum on axis and is described by a superposition of 0th and 1st order diverging Bessel beams with opposite circular polarizations. These calculations were compared with experiment and the agreement was very close [9].…”

Two-section singlemode lasers based on slots suitable for photonic integration

“…This approach has led to detailed predictions of the intensity distributions of conically diffracted paraxial light beams [6][7][8]. 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].…”