Diffraction regime of an intracavity thin grating

In this paper, we propose to investigate the case when both the incident beam and the main diffraction order are Fabry-Perot resonant, at Bragg incidence on a thin unslanted grating. We calculate the intensities of the most important diffraction orders and show what conditions must be fulfilled to obtain a Bragg diffraction regime where all diffracted energy is concentrated in a single diffraction order