Question

Briefly, what are ‘grating ghosts’ and what are they caused by?

Answer 1

False lines appearing in grating spectra as a result of periodic errors in the shape or location of the ruled grooves are commonly called ghosts

If the diffraction grating has periodic ruling errors, a ghost, which is not scattered light, will be focused in the dispersion plane. Ghost intensity is given by:

Ghosts are focused and imaged in the dispersion plane of the monochromator.

Stray light of a holographic grating is usually up to a factor of ten times less than that of a classically ruled grating, typically non-focused, and when present, radiates through 2 pi steradians.

Holographic gratings show no ghosts because there are no periodic ruling errors and, therefore, often represent the best solution to ghost problems.