Calculating the Spectral Bandpass of the RSM
EISW for Various Intermediate Slits and Entrance/Exit Slit Combinations
(Rows/columns represent values for entrance/exits slits. All entries are in millimeters.)
intermediate slit = 0.12 mm
| |
0.12 |
0.60 |
1.24 |
0.12 |
0.12 |
0.12 |
0.12 |
0.60 |
0.12 |
0.60 |
0.60 |
1.24 |
0.12 |
0.60 |
1.24 |
intermediate slit = 0.20 mm (scan disk)
| |
0.12 |
0.60 |
1.24 |
0.12 |
0.20 |
0.20 |
0.20 |
0.60 |
0.20 |
0.60 |
0.60 |
1.24 |
0.20 |
0.60 |
1.24 |
intermediate slit = 0.50 mm (scan disk)
| |
0.12 |
0.60 |
1.24 |
0.12 |
0.50 |
0.50 |
0.50 |
0.60 |
0.50 |
0.60 |
0.60 |
1.24 |
0.50 |
0.60 |
1.24 |
intermediate slit = 0.60 mm
| |
0.12 |
0.60 |
1.24 |
0.12 |
0.60 |
0.60 |
0.60 |
0.60 |
0.60 |
0.60 |
0.60 |
1.24 |
0.60 |
0.60 |
1.24 |
intermediate slit = 1.00 mm (scan disk)
| |
0.12 |
0.60 |
1.24 |
0.12 |
1.00 |
1.00 |
1.00 |
0.60 |
1.00 |
1.00 |
1.00 |
1.24 |
1.00 |
1.00 |
1.24 |
intermediate slit = 1.24 mm
| |
0.12 |
0.60 |
1.24 |
0.12 |
1.24 |
1.24 |
1.24 |
0.60 |
1.24 |
1.24 |
1.24 |
1.24 |
1.24 |
1.24 |
1.24 |
|
The Spectral Bandpass of the RSM can be calculated as the product of the effective instrument slit width (EISW) and the reciprocal dispersion (RD) of the gratings:
BANDPASS = EISW x RD.
The rule for determining EISW is as follows:
The EISW is equal to the width of the intermediate slit. The exception is when the other slits are wider than the intermediate slit, in which case the EISW is equal to the width of the narrower of the other slits.
Nominal Reciprocal Dispersions of Some Common Gratings
(Precise value varies with wavelength.)
Groove Density
(l/mm) |
Reciprocal Dispersion
(nm/mm) |
| 400 |
9.4 |
| 600 |
6.4 |
| 1200 |
3.1 |
| 2400 |
1.4 |
|
Discussion
It is important to note that the above EISW data represent the full-width-half-maximum (FWHM) values of the instrumental line profiles for the various slit combinations. This means that although two different configurations will provide the same bandpass, they will, in general, produce different instrumental line profiles. For a given bandpass, the most efficient performance (highest luminosity, lowest stray light) is obtained when all slits are of equal width. With the standard RSM slit set, this is not achievable when a Scandisk cartridge is employed. In this case, the closest approximation should be used. For example, in the case of the 0.2 mm scandisk, a 0.12 mm and a 0.6 mm slit are appropriate.
Full list of RSM components
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