Dichroism for Orbital Angular Momentum using Stimulated Parametric Down   Conversion
  We theoretically analyze stimulated parametric down conversion as a means to produce dichroism based on the orbital angular momentum (OAM) of an incident signal field. The nonlinear interaction is shown to provide differential gain between signal states of differing OAM, the peak gain occurring at half the OAM of the pump field. 
Joseph Lowney, Thomas Roger, Daniele Faccio, and Ewan M. Wright
physics.optics