Conical refraction with low-coherence light sources.

V Yu Mylnikov,V V Dudelev,G S Sokolovskii,K A Fedorova,S N Losev,E U Rafailov

doi:10.1364/oe.27.025428

Abstract

We report on conical refraction (CR) with low-coherence light sources, such as light-emitting diodes and decoherentized HeNe laser radiation, and demonstrate different CR patterns. In our experiments, a variation of the pinhole sizes from 25 to 100 µm and the distances to pinhole from 50 to 5 cm reduced spatial coherence of radiation that resulted in the disappearance of the dark Poggendorff's ring in the Lloyd's plane. This is attributed to the interference nature of the Lloyd's distribution and found to be in excellent agreement with the paraxial dual-cone model of conical refraction.

Highlights

Lloyd did not report on a dark ring in the circular intensity pattern of Conical Refraction (CR) that was observed by Poggendorff a few years later in 1839 [3]
We present the results of experiments on conical refraction with narrow-apertured low-coherence light sources, such as light-emitting diodes (LEDs) and a HeNe laser, and demonstrate that an increase of the pinhole size or reduction of the distance to pinhole results in the disappearance of the dark ring separating the Lloyd’s counterparts
We utilized LED radiation pinholed to 25 or 100 μm in a distance of 50 mm or 500 mm and HeNe laser light decoherentized with a rotating blurry plate

Summary

Introduction

The dark Poggendorff’s ring remained unexplained for a long time after its discovery until the Voigt’s publication in 1905 [12] His interpretation relays on proportionality of the divergence of the conical refraction pattern inside a biaxial crystal to the divergence of an initial beam propagating along the optical axis. We present the results of experiments on conical refraction with narrow-apertured low-coherence light sources, such as light-emitting diodes (LEDs) and a HeNe laser, and demonstrate that an increase of the pinhole size or reduction of the distance to pinhole results in the disappearance of the dark ring separating the Lloyd’s counterparts We attribute this to the interference nature of the Lloyd’s distribution and explain the experimental data within the paraxial dual-cone model of conical refraction [15,16]

Theory

Experiment

Conclusion