| Entrance Slit |
||
|
The function of the entrance slit is to define a clear-cut object for the optical bench. The size (width (Ws) ´ height (Hs)) of the entrance slit is one of the main factors that affect the throughput of the spectrograph. The image width of the entrance slit determines the spectral resolution of the spectrograph when it is greater than the detector array pixel width (see equation 3-1). Both the throughput and resolution of the system should be balanced by selecting a proper entrance slit width. The image width of the entrance slit (Wi) can be estimated as: Wi = (M2×Ws2+Wo2)1/2 (Equation 4-4) |
|
|
where M is the magnification of the optical bench set by the ratio
of the focal length of the focusing mirror (lens) to the collimating
mirror (lens), Ws is the width of the entrance slit, and
Wo is the image broadening caused by the optical bench.
For a CZ optical bench, Wo is on the order of a few tens
of microns. So reducing the width of the entrance slit below this
value won't help much on improving the resolution of the system. The
axial transmissive optical bench provides much smaller Wo.
Thus it can achieve a much higher spectral resolution. Another limit
on spectral resolution is set by the pixel width (Wp) of
the array detector. Reducing Wi below Wp won’t
help to increase resolution of the spectrograph. Under condition that the resolution requirement is satisfied, the slit width should be chosen for as wide as possible to improve the throughput of the optical bench. The standard slit width for B&W TEK, INC. spectrometers are 10, 25, 50, 100, 200 |
||
|
Return to
Econic Product page |
||
