RSS Fabry-Perot System
The SALT RSS Fabry-Perot system provides spectroscopic imaging over the whole RSS science field of view (8 arc min diameter) in the wavelength range 430-860 nm with spectral resolutions ranging from 300-10,000.
The system employs a set of three etalons with gap spacings of ~6, ~28 and ~136 µm respectively. The etalons are referrred to as the small gap (SG), medium gap (MG) and large gap (LG) etalons respectively. The SG etalon may be selected on its own for use in tunable filter (TF) and low resolution (LR) modes. The MG or LG etalon are selected for use in medium resolution (MR) and high resolution (HR) mode respectively. Both these etalons are always used in conjunction with the SG etalon which effectively acts as a transmission filter in this case.
A set of 40 blocking filters are employed to select the transmission order. Filter transmission curves are here.
The table below summarises the key characteristics of the system in the various modes.
TF mode | LR mode | MR mode | HR mode | |
|---|---|---|---|---|
Bandpass | 430 - 860 nm | 430 - 860 nm | 430 - 860 nm | 430 - 860 nm |
Free Spectral Range at 650 nm | 364 A | 182 A | 75 A | 15 A |
Resolution at 650 nm | 323 | 779 | 1494 | 8777 |
Finesse at 650 nm | 16.7 | 21.9 | 17.3 | 21.0 |
Effective plate gap | 5.8 µm | 11.5 µm | 28.2 µm | 135.9 µm |
Wavelength drift | < 1 A per hour | < 1 A per hour | < 1 A per hour | TBD |
A detailled description of the system is given in the paper by Naseem Rangwala, Ted Williams and their collaboraters:
The following 3 etalon reports detail the technical details of each etalon.
Tables containing the FWHM of the spectral resolution, the resolution and free spectral range of each etalon as a function of wavelength are included in each report. This information is helpful for proposal planning.
Additionally, Ted Williams has produced an Introduction to Fabry-Perot on SALT.
