Grating ghosts

Figure 5.17 Rotational Raman spectrum of N2 (the lines marked with a cross are grating ghosts and not part of the spectrum)...

Fig. 20. Resonance Raman scattering from cytochrome c at several excitation wavenumbers. In the top spectrum the symmetries and wavenumbers of the prominent bands are labelled. For ease of identification they42 band at 1585 cm is labelled in all spectra. The band labelled by an asterisk is a grating ghost. The ice line near 3100 cm may be used as an intensity reference.

Rowland ghost spect A false spectral line produced by a diffraction grating, arising from periodic errors in groove position. ro,l3nd, gost ... 

Ghosts Double images in the output of a grating, the result of imperfections in the ruling engine used in its preparation. 

Rowland ghosts spurious intensity maximum spurred from periodic errors in the spacing of the ruled grooves in a diffraction grating. 

Tian JJ, Zhang Q, Han M. Distributed fiber-optic laser-ultrasound generation based on ghost mode of tilted fiber Bragg gratings. Opt Express 2013 21 6109-14. 

Errors in mirror position or optical retardation produce a variety of unwanted effects in the final specrim including additional noise, degradation of the spectral resolution, and ghost or satellite specral lines. These are all similar to the effects which are caused by ruling errors on gratings in dispersive instruments. 

The choice of a spectrometer depends on its intended use. Most present-day instruments use a grating as the spectral dispersing element. A wide variety of excellent gratings is currently available. They are supplied with certification as to their precision, blaze efficiency, and freedom from ghost lines, and are generally of high quality. 

However, one of the problems with gratings is the presence of ghosts between the orders due to spurious reflections. This effect is almost completely eliminated when master holographic gratings are used. 

Holographic gratings, because of their greater perfection with respect to line shape and dimensions, provide spectra that are relatively free of stray radiation and ghosts (double images). 

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