Abstract

The concern with investigation of phase distribution of optical vortices has been growing because of its applications such as nonlinear spectroscopy, classical or quantum information processing and communications. Hence, precise and quantitative evaluation of the orbital angular momentum (OAM) state expressed by OAM spectrum is an essential issue. Although there are several methods developed for OAM detection, most of them do not provide us information on OAM distribution but only the dominant topological charge number. Indeed, almost the only way to measure OAM spectrum has been by using of a holographic phase grating generated on a spatial light modulator (SLM) [1] so far. However, this method still has limitation especially in the bandwidth. In the case of ultrabroadband beam, needless to say, such diffraction devices cause non-negligible angular dispersion, which hampers reliable detection of the diffracted signals. In the present paper, we demonstrate a new method to obtain OAM spectrum on the basis of electric-field reconstruction in spatial domain from interferograms, without using diffraction effects. Our method is applicable to ultrabroadband optical vortices, even in few-cycle regime [2].

© 2013 IEEE