Measurement of the angle-angular momentum uncertainty of a light beam

Abstract

The summary form only given. One of the many forms of the uncertainty principle concerns angular position and angular momentum. We demonstrate this in the case of light: the more the angular position of a light beam is restricted by passing it through a radial aperture, the larger the spread in the beam's angular-momentum components. We prepare laser beams in different angular momentum states by reflecting them from a phase hologram, which determines the orbital-angular-momentum state, and passing them through a quarter-wave plate, which determines the spin state. We can measure the angular-momentum components in the beam in the form of resonances of a novel beam-rotating ring resonator. Our results are in broad agreement with the predictions of the uncertainty principle.