Holographic grating
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 may exhibit less scattered light than ruled gratings. Due to their sinusoidal groove profile, 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.
