Holographic grating

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A holographic grating is a type of diffraction grating formed by an interference-fringe field of two laser beams whose standing-wave pattern is exposed to a polished substrate coated with photoresist. Processing of the exposed medium results in a pattern of straight lines with a sinusoidal cross section.

Holographic gratings produce less stray light than ruled gratings. They can also be produced with up to 3,600 grooves per millimeter, corresponding to a groove spacing (also called a grating period) of 278 nm, for greater theoretical resolving power. Due to their sinusoidal cross section, holographic gratings cannot be easily blazed and their efficiency is usually considerably less than a comparable ruled grating. However, an exception exists when the ratio of the period to the wavelength is near one; in this case, a holographic grating has virtually the same efficiency as the ruled version.

Holographic master gratings are replicated by a process identical to that used for ruled gratings.