Newport Cornerstone 130B, User Manual

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90088262 MCS130B
CORNERSTONE 130B MONOCHROMATORS
21
6.1
34B
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 manufac t uring
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 s tray
light inside the monochromator.
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.
Figure 14: Grating Properties Table
GRATING PROPERTIES
Configuration
Grating
Position Type
Groove
Density
(lines/mm)
Blaze
Wavelength
(nm)
Reciprocal
Dispersion
(nm/mm)
High
Resolution
#1 Ruled 2400 240 2.7
#2 Ruled 1200 500 5.3
Holographic
#1 Holographic 1200 250 5.5
#2 Holographic 1800 500 3.3
Extended
Range
#1 Ruled 600 400 11
#2 Ruled 600 1000 10.6
Near IR
#1 Ruled 600 1000 10.6
#2 Ruled 300 2000 21.2