Although sinusoidal holographic gratings do not have the triangular groove profile found in ruled gratings, holographic gratings may still exhibit blazing characteristics. For this reason, it is not correct to say that all blazed gratings have triangular profiles, or that all blazed gratings are ruled gratings – blazing refers to high diffraction efficiency, regardless of the profile of the grooves or the method used to generate them.
There are some case in which it would be preferable for a holographic grating to have a triangular groove profile rather than a sinusoidal profile. The method of using standing waves to record the grooves (see Holographic Diffraction Gratings) was developed by Sheridon and improved by Hutley.
Another useful technique for rendering sinusoidal groove profiles more nearly triangular is ion etching. By bombarding a surface with energetic ions, the material can be removed (etched) by an amount per unit time dependent on the angle between the beam and the local surface normal. The etching of a sinusoidal profile by an ion beam provides a continuously varying angle between the ion beam and the surface normal, which preferentially removes material at some parts of the profile while leaving other parts hardly etched. The surface evolves toward a triangular groove profile as the ions bombard it.
Other method for generating blazed groove profiles have been developed, but the Sheridon method and the method of ion etching are those most commonly used for commercially-available gratings.
For footnotes and additional insights into diffraction grating topics like this one, download our free MKS Diffraction Gratings Handbook (8th Edition)
Download a Handbook
Ultra-High Velocity