Editing Diffraction grating (section)

=== SR (Surface Relief) gratings ===
SR gratings are named due to its surface structure of depressions (low relief) and elevations (high relief). Originally, high-resolution gratings were ruled by high-quality ''[[Dividing engine|ruling engines]]'' whose construction was a large undertaking. [[Henry Joseph Grayson]] designed a machine to make diffraction gratings, succeeding with one of 120,000 lines to the inch (approx. 4,724 lines per mm) in 1899. Later, [[lithography|photolithographic]] techniques created gratings via [[holography|holographic]] interference patterns. A [[holographic grating]] has sinusoidal grooves as the result of an optical sinusoidal interference pattern on the grating material during its fabrication, and may not be as efficient as ruled gratings, but are often preferred in [[monochromator]]s because they produce less [[stray light]]. A copying technique can make high quality replicas from master gratings of either type, thereby lowering fabrication costs.

Semiconductor technology today is also used to etch holographically patterned gratings into robust materials such as fused silica. In this way, low stray-light holography is combined with the high efficiency of deep, etched transmission gratings, and can be incorporated into high-volume, low-cost semiconductor manufacturing technology.