2-WAVE DIFFRACTION OF QUASI-MONOCHROMATIC LIGHT BY A VOLUME GRATING DEPOSITED ON A THICK TRANSPARENT PLATE

The diffraction by a Bragg volume grating deposited on a transparent parallel plate is analysed in the case of reduced temporal coherence. When the grating is thinner, and the substrate is thicker than the coherence length, the summation of multiple-beam series, involving coherent diffraction coefficients of the periodic film and incoherent multiple reflected intensities inside the plate, is shown to given simple analytic expressions of the diffraction efficiencies of the device. Numerical results of this model are compared with those obtained by spectral integration. The multiple-beam model provides an accurate representation of the energy balance between the diffracted orders, and is particularly useful for determining the energy losses due to spurious reflections.