Enhancement of diffraction efficiency for optical gratings

A method to increase the diffraction efficiency for optical gratings is proposed. Using a simple glass plate sitting parallel to the top of a grating surface, one can form an air gap between the surfaces of the grating and the glass plate to reflect a grazing-incident light beam and make diffraction through multiple reflection of the beam between the grating and glass plate surfaces. As a result, this device can efficiently enhance the grating efficiency by diffracting the input beam energy into various diffraction orders.