Polarisation distribution for internal conical diffraction and the superposition of zero and first order bessel beams

Abstract

Internal conical refraction leads to the formation of zero (J0) and first order (J1) Bessel beams in superposition. The (J0) beam retains the input circular polarisation and the (J1) has opposite polarisation but with a single phase change around the beam axis giving it ? optical angular momentum per photon. This results in the conical beam having ? ? net optical angular momentum per photon. This provides a simple system in which a beam of 0, ? and ? optical angular momentum can be easily generated and selected with use of only a circular polariser. In the far field the characteristic Bessel beam structures are formed and can be made non-diverging with use of a lens. We report the formation of non-diverging Bessel beam of core diameter (a) of 5.7?m over a maximum non-diverging core length of 1(?.05)mm. However due to the fine structure of the conical beam at its beam waist position two cores are produces and are of opposite phase.