Integral and fractional orbital angular momentum of light
Orbital angular momentum of light is a new field of research which is concerned with the mechanical and optical effects of light with a helical phase structure. In this thesis we ask fundamental questions on the properties of light carrying orbital angular momentum. We discuss the uncertainty relation for angle and angular momentum on the example of orbital angular momentum of light. The lower bound in the angular uncertainty relation is state dependent, which requires a distinction between states satisfying the equality in the uncertainty relation and states giving a minimum in the uncertainty product. We examine these special states and their uncertainty product. We show that for both kinds of states, the uncertainty product can be surprisingly large. We propose an experimentally testable criterion for an EPR paradox for orbital angular momentum and azimuthal angle. The criterion is designed for an experimental demonstration using orbital angular momentum of light. For the interpretation of future experimental results from the proposed setup, we include a model for the indeterminacies inherent to the angular position measurement. We show how angular apertures can be used to determine the angle, and we discuss the effects of this measurement on the proposed criterion. We show that for a class of aperture functions a demonstration of an angular EPR paradox, according to our criterion, is to be expected. The quantum theory of rotation angles is generalised to non-integer values of the orbital angular momentum. This requires the introduction of an additional parameter, the orientation of a phase discontinuity associated with fractional values of the orbital angular momentum. We apply our formalism to the propagation of light modes with fractional orbital angular momentum in the paraxial and non-paraxial regime.