Grating Types; Figure 15: Grating Properties Table - Newport Oriel MS260i Series User Manual

6.1 GRATING TYPES

Ruled grating masters are produced using a ruling engine with an extremely fine cutting tool.
Holographic gratings (also called interference gratings) are produced by recording interference
fringes in photoresist. The different techniques cause some differences in performance.
Holographic gratings are most frequently available at high groove densities due to manufacturing
limitations inherent in the technology. They are generally favored for work in the UV and through the
visible to about 600 nm. Holographic gratings produce less scattering, thereby reducing stray light
inside the spectrograph.
Ruled gratings typically have higher efficiencies. They may have periodic errors in the grating grooves
caused by minor defects in the ruling machine, resulting in anomalous readings or "ghosts".
Holographic gratings do not suffer from ghosts, so interpretation of line spectra is simplified.
The signal-to-noise ratio (SNR) is the ratio of diffracted energy to unwanted light energy. Although it
may be assumed that increasing diffraction efficiency will increase SNR, stray light usually plays the
limiting role in the achievable SNR for a grating system. Note that the actual signal to noise ratio will
depend on the spectral content of the incident light and the detector.
Configuration
High Resolution
Holographic
Extended Range
Wide Bandwidth
*** Bandpass is measured across a 1 inch array, with grating centered at blaze wavelength.
GRATING PROPERTIES
Grating
Position Type
#1 Ruled
#2 Ruled
Ruled
#3
Holographic
#1
Holographic
#2
Ruled
#1
Ruled
#2
Ruled
#3
Ruled
#1
Ruled
#2
Ruled
#3

Figure 15: Grating Properties Table

1/4M IMAGING SPECTROGRAPHS
Groove Blaze
Density Wavelength
(lines/mm) (nm)
1200 360
1200
500
1200
750
1200
250
1800
500
600
200
600
400
600
1000
300 500
300 1000
300 2000
M74050
21
Array
Bandpass
(nm) **
80
81
80
80
50
160
165
160
325
325
325