Counterpropagating nondiffracting beams through reflection gratings

We investigate the counterpropagation of paraxial nondiffracting optical beams through a medium hosting a bulk reflection grating in the quasi-Bragg matching condition. The impact of the relative magnitude of the Bragg detuning parameter and the grating depth on the plane wave dispersion relation allows us to identify three distinct regimes where counterpropagation and interaction of nondiffracting beams show qualitatively different features, encompassing longitudinally invariant, periodic or exponential intensity profiles. In one of the identified regimes the dispersion relation is not monotonic and the consequent 'longitudinal degeneracy' allows the investigation of new class of nondiffracting beams characterized by a double spectral ring profile. (c) 2007 Optical Society of America.