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Version 4.2 rev 06 Oct 2020
8.2 x 8.2 mm / 512 x 512 sensor
Lowest Noise Imaging EMCCD
Mechelle
APPENDIX B: REFERENCE INFORMATION
ecHelle tHeory
Echelles are a special class of high-angle gratings, rarely used in orders below m = 5 and sometimes used in orders
beyond 100. Because of order overlap, some type of ltering is normally required with higher-order grating systems.
This can take several forms, such as cut-off lters, detectors insensitive to longer wavelengths, or cross-dispersion
in the form of prisms or low-dispersion gratings. The latter approach leads to a square display format suitable for
corresponding types of array detectors.
Figure 28 below shows the grating angles and gure 30 shows the optical layout of the spectrograph.
Figure 28: Equation Angles
α = incidence angle
β = diffraction angle
d = grating constant (d ≈ 5 - 30 μm)
f = focal length
θ = blaze angle ≈ 60°
m = diffraction order (m ≈ 50)
N = total number of grooves W/d
W = width of grating
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