Spectroscopy, from initiation to performance
13 380,00 € incl. VAT - 11 150,00 € excl. VAT
The eShel III spectroscope is a professional-grade, fibre-optic, multi-order (Echelle grating) instrument.
It combines high resolution (R = 10,000) with a wide spectral range (from 370 to 910 nm) – this is useful, for example, for the study of exoplanets.
The eShel III spectroscope must be fitted with the FIGU, the calibration module and the optical fibres in order to operate. The ‘complete eShel III system’ (ES0043) comprises all of these components.
| Description | Shelyak ref. | Included |
Acc. type
|
Cooled
|
Comment
|
| Camera Atik 460EX Mono | SE0124 | Camera Science | yes | The standard CCD camera for the eShel II | |
| Caméra ASI2600MM-Pro | EL0271 | Camera Science | yes | New generation CMOS camera |
The eShel III spectroscope enables work across a wide spectral range (370 to 910 nm) at high resolution (R = 10,000). This is made possible by the use of multiple orders (in this case, between 25 and 60); an Echelle spectrum reads ‘like a book’: the end of one order is found at the start of the next.
The decision was taken to propose a fibre-optic solution in order to improve the accuracy of radial velocity measurements (the instrument is separate from the telescope, ideally housed in a temperature-controlled room, and is therefore not subject to any flexure) and to enhance user comfort. The optical fibre is 50 µm in diameter.
We have developed this instrument based on our experience with the Musicos and Narval professional spectroscopes.
This technique enables high spectral resolution to be achieved as it use the higher diffraction orders of a diffraction grating (orders greater than 20). The resulting spectrum passes through a cross-disperser – a prism in this case – which separates the successive orders across the entire surface of the camera’s sensor. This provides the entire spectral range within the visible spectrum, spanning several tens of orders.
Schematic diagram of an Echelle spectrograph (© François Cochard)
Example of an Echelle spectrum: spectrum of a Be star (the Balmer emission lines are visible).
The image is colourised afterwards.
Spectrum of Sunlight
Orders #25 to #60 are uniformly focused… even slightly beyond these limits.
Spectrum of Chi Oph Be star
This allows us to process orders #25 through #60 and extend the usable spectral range from approximately 370 to 910 nm. 
The motorised version of this lens comes with a PrimaLuce Lab focuser, which allows for remote focusing (ideal for use over long distances or when the spectrograph is not located next to the control PC).
There is also a manual version fitted with a helical focuser
Applications
By Olivier Garde The eShel II spectroscope features an 85-mm focal-length camera lens that is no longer manufactured; an alternative had to be found, so Shelyak Instruments designed its own 122-mm focal-length Petzval-type lens. This “custom” design has made it...
You'll find all our Demetra video tutorials on this web page. Demetra is a free software package for processing spectra from the ALPY 600, LISA and eShel spectrographs from the Shelyak Instruments range. Playlist of Demetra tutorials Tutorial #1 Introduction to...
