Newport ORIEL Instruments Cornerstone 260 - Grating Types

MCS260
CORNERSTONE 260 MONOCHROMATORS
22
6.1 GRATING TYPES
Ruled grating masters (also called interference gratings) are produced using a ruling engine with an
extremely fine cutting tool. Holographic 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.
Holographic gratings 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
monochromator. 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.
Ruled gratings typically have higher efficiencies. Ruled gratings 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.
Figure 16: Grating Properties Table
GRATING PROPERTIES
Configuration
Grating
Position
Type
Groove
Density
(lines/mm)
Blaze
Wavelength
(nm)
Reciprocal
Dispersion
(nm/mm)
High Resolution
#1
Holographic
1200
250
3.2
#2
Ruled
1200
350
3.2
#3
Ruled
1200
1000 3.2
High Resolution
Extended Range
#1
Ruled
1200
350
3.2
#2
Ruled
1200
750 3.1
#3
Ruled
600 1000 6.4
UV-VIS
#1
Ruled
600
200 6.4
#2
Ruled
600
400
6.5
Extended Range
#1
Ruled
600
400 6.5
#2
Ruled
600
1000
6.4
VIS-NIR
#1
Ruled
300 500 12.8
#2
Ruled
600 1000 6.4
#3
Ruled
300 2000 12.9