21
Version 4.2 rev 06 Oct 2020
8.2 x 8.2 mm / 512 x 512 sensor
Lowest Noise Imaging EMCCD
Mechelle
2.2 i
nteRnal
c
oMponents
oF
tHe
M
ecHelle
The main internal parts of the Mechelle are summarised below (refer to Appendix B for the principles of operation and
also
).
Figure 2: Internal Components of the Mechelle (for illustration only)
Entrance Window
The entrance and (exit) window prevents ingress of dust and contaminants, and allows the internal space to be sealed
and purged with N
2
for best UV transmission.
Correction Lenses
:
Two custom-made correction lenses are utilised to achieve good imaging resolution.
Collimating lens
This element ensures that light incoming on the dispersive element (prism) is collimated.
Echelle Grating
This type of grating provides good efficiency performance over a large number of orders and wavelength range. Its
groove density also dictates the spectral resolution.
Double Prism
The broadband double prism design is used to achieve semi-equal order spacing for ultra-low cross-talk.
Exit Window
The exit (and entrance) window prevents ingress of dust and contaminants and allows the internal space to be sealed and
purged with N
2
for best UV transmission.
Purge Ports
The shutter housing can also be flushed with dry gas to remove any water vapour using the two purge ports to maximize
UV light transmission..
Sealed, N
2
filled
Chamber
Correction lens 2
Correction lens 1
Entrance
Window
Echelle
Echelle
Grating
Grating
Focusing
Mirror
Double
Prism
Flatfield
Lens
Collimating
Collimating
Mirror
Mirror
Shutter
Housing
To Camera
(Detector)
Input
from Light
Source
Shutter
(if fitted)
Purge
Port
Purge Port
Slit
Slit
Exit Window
Exit Window
