Angular diffraction

Angle and angular momentum are linked by a Fourier transformation. A restriction of the angular range within an optical beam profile therefore generates orbital angular momentum (OAM) sidebands on the transmitted light. We interpret this phenomenon as angular diffraction: a mask that blocks light within one or several angular ranges is the angular analogue of a single slit or a diffraction grating, respectively. In the OAM spectra of light transmitted through angular masks we observe the typical sinc(2) envelope known from single slit diffraction, and in particular the suppression of OAM sidebands. This is the angular analogy to missing orders observed for a linear diffraction grating.