Exposure by two laser beams that form an interference pattern on the surface. Holographic gratings or, as they are sometimes called, interference gratings, are recorded from an interference pattern, in contrast to the classical gratings which are mechanically ruled by a diamond tip.
Holographic gratings are available either as original gratings, or replicated gratings.
The interference pattern formed where two beams from a laser intersect, is used for exposing a photosensitive layer on top of a glass substrate. A chemical treatment of the film selectively dissolves the film to form a relief pattern on the substrate. The corrugated surface can be used as a transmission grating, but normally it is coated with a thin metallic layer to give a reflection grating. After development and metal coating. Holographic gratings of standard type Plane waves are used for exposing standard piano holographic gratings.