Measuring the rotation rates of superpositions of higher-order Bessel beams

Experimental measurements are reported of the rotation rates of superpositions of higher-order Bessel beams. Digitally generated phase masks of two annular rings, were imprinted on a spatial light modulator and used to obtain superpositions of higher-order Bessel beams of the same order but of opposite topological charge. Such a superposition field carries on average zero orbital angular momentum, yet exhibits a rotation in the intensity pattern: the resultant field rotates at a constant rate about the optical axis as it propagates. The rotation rates of the generated fields were measured for different orders and for various values of the difference between the wave-vectors of the superimposing beams, and are shown to be in good agreement with that predicted theoretically.