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Echelle, cross-disperser and spectral format

Delivered in August 2004 by the Spectra-Physics (formerly Richardson Gratings), the echelle grating, made on a Zerodur substrate, is blazed at 76$^o$ and has 41.59 gr/mm over a 102$\times$408 mm ruled area. It works in Littrow configuration with a small 0.9$^{\circ}$ off-plane angle. Such a small angle introduce no evident line tilt, below 0.2 pixel everywhere on the CCD focal plane.

A 140x160x160 mm prism with an apex angle of 53.1$^{\circ}$ has been realized by the Società Italiana Lavorazione Ottiche and delivered in February 2005. This acts as cross-disperser. Interorder separation is minimum in the red side of the echellogram. SF1 glass has been chosen after trade-off between transmission over the whole spectral range, dispersion, and cost for raw material. The prism is anti-reflection coated with an average efficiency better than 90%.

The 3881-7250Å spectral range is split in 56 orders with no gaps and overlapping for two fibers. Observations using only one fiber and with some gaps are possible with the 3756 - 8351 Å interval.


next up previous contents index
Next: Camera optimization Up: CAOS - The new Previous: Collimators   Contents   Index
Innocenza Busa' 2005-11-14