VAGR Integral Field Spectrograph

This instrument is the realisation of an elegant solution proposed by G.Courtes (1982) to achieve spectroscopic analyses of extended objects with a full 2D spatial coverage. The first realisation was integral field spectrograph TIGER on CFHT, now OASIS project. This concept, based on a micro - lenses array, allows to retrieving tree dimensions (2D space and 1D wavelength) information on 2D detector without the loss of sensitivity associated with time-scanning schemes. Another solution was realised on 6 m telescope in MPFS spectrograph where fibres were used to rearrange micro-pupils into pseudo slit, which allows having wide spectral range.

Optical Design

The schematic layout of the optical configuration is ilustrated in this picture. The field of view is enlarged and focused on the micro-lenses array by an objective and field lens, which also makes telecentric beams on the micro-lenses array. The array perfumes the spatial sampling. Each micro-lens gives an image of the exit pupil whose size is much smaller than the input lens diameter. The remaining part is classical wield field grism-based spectrograph. Each micro-pupil, dispersed by grism, gives a spectrum on the CCD. A slight rotation between the dispersion axis and the micr-lenses array, combined with wide band interference filter, avoids overlapping between spectra. In spectrograph only classical refractive optics is used.

Instrument is mounted on "Bonnette" - Prime focus guiding pointing system of 2.6m telescope of Byurakan Observatory. In the table the main parameters of VAGR spectrograph are presented.

Table

Enlarger focal length

10mm

Micro-lenses array 40x40 lenses
Micro-lenses diameter 1.1mm
Micro-lenses focal length 8.9mm
Collimator focal length 250mm
Collimator aperture ratio f/2
Collimated beam 30mm
Camera focal length 110mm
Camera aperture ratio f/2
Grism 600 groves
CCD Thomson 1060x1028x19mm
Field 40x40 arcsec
Scale 1.2 arcsec/micro-lens
Wavelength range 210A
Spectral resolution 1800

Recorded data cube

40x40x128

Available Filters

#

CWL(A) FWHM(A) Tmax(%) Profile
1 6560 80 75 box
1

6732

75

72

box


     

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