Duality violation from a grating

Diffraction orders in the continuous wave regime generated by a Ronchi transmission grating in a standard threshold configuration are shown theoretically to violate quantum duality for a locally real representation. The phenomenon superficially resembles Rayleigh anomalies but is notably distinguished from those anomalies by a prediction of probability non-conservation. This prediction is experimentally tested with a 633 nm laser beam at normal incidence on gratings giving that threshold condition for the \pm 3rd order pair. Transient intersection of the Oth order with an independent 633 nm laser beam demonstrates a duality-violating probability non-conservation in good agreement with the theoretical prediction.