Grating master

Modern gratings are interference based. That is, they (the master gratings, from which copies are made) are manufactured by the interference pattern of two lasers impinging on a photosensitive surface (thus, the term holographic). This... 

Replica grating An impression of a master grating used as the dispersing element in most grating instruments, owing to the high cost of a master grating. 

Replica gratings arc formed front a master grating by a liquid-resin casting process that preserves virtually perfectly the optical accuracy of the original master grating on a clear rosin surface. This surface is usually made reflective by a coating of aluminum, or sometimes gold or platinum. 

Ruled gratings are mainly used in AA instruments. Holographic gratings have less irregularities and therefore lower stray radiation, but this is not so important in AAS as it is, for example, in plasma-AES. From the ruled master gratings (often aluminium) copies can be prepared, which are less expensive. 

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