Theoretical study of the diffraction anomalies of holographic gratings

Recent experimental measurements made by Hutley in the visible region on holographic diffraction gratings have revealed that serious discrepancies exist between predictions based on an infinite conductivity grating theory and the actual behaviour of optical gratings. It is shown here that these discrepancies can be removed if finite conductivity effects are taken into account by the grating theory. Grids of efficiency curves calculated for gratings having sinusoidal profiles covered with aluminium are given here. It is shown how these curves may be used to estimate the groove depths of holographic gratings from their experimental efficiency curves, using as an example the data Hutley. The importance of profile distortion on the form of the efficiency curves is made evident. Theoretical data is given on the best mount for holographic gratings, and also on the range of groove depths which gives them the best blaze.