Measuring the orbital angular momentum density for a superposition of Bessel beams

In this report we theoretically calculate and experimentally measure the OAM density of a coherent superposition of both symmetric and non-symmetric non-diffracting Bessel beams. Although the intensity pattern of the superimposed field rotates at a fixed angular velocity (which is due to the differing wave-vectors of the component fields), we show that the magnitude and direction of the OAM is dependent on the radial position within the field. We outline a simple approach using only a spatial light modulator to measure the OAM density for a superposition of non-diffracting Bessel beams. Our quantitative measurements are in good agreement with predicted values.