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.