image Arago UV Spectrograph image Arago UV detector image

UV spectrograph

The UV light exiting from the polarimeter is reflected by a dichroic and enters a spectrograph designed to cover the UV wavelengths from 119 to 320 nm. The beam first reaches an off-axis parabolic collimator that sends the beam to an echelle grating. The cross-dispersion is made with a spherical concave grating. The full spectral range is fitted within a single image on a CMOS detector.
UV spectra with a resolution of R>=25000 are recorded over the full wavelength range from 119 to 320 nm. This range includes many useful spectral lines, in particular resonance lines of highly ionised chemical species, as well as hydrogen lines such as Lyman_alpha.