Signal-to-Noise Ratio of Holographic Gratings

In many applications, the most important system parameter is the signal-to-noise ratio. The signal level is proportional to light collection properties and efficiency of the grating. For a classically ruled grating, the noise arises from ghosts (associated with periodic errors in the lead or pitch of the high precision screw), and from stray light due to random, non-periodic surface defects and the roughness of the reflecting surfaces.

Holographic recording produces grooves that are perfectly equi-spaced, completely eliminating all ghosts due to periodic errors. The overall quality of the grating surface is such that imperfections and roughness are considerably less than those found in classically ruled gratings, thus reducing stray light. In addition, the holographic technique is well-suited for producing large numerical aperture concave gratings (F/2 or even more).

As a result, holographic gratings generally present a much higher signal-to-noise ratio compared to classically ruled gratings.