Dr. Filippo M. ZerbiOPTICON JRA6 CoordinatorINAF- Osservatorio di BreraVia Bianchi, 46I-23807 Merate (Lc)ItalyTelephone: +39 039 9991149E-mail: zerbi@merate.mi.astro.it

Dr. John K. DaviesOPTICON Project ScientistUK Astronomy Technology Centre,Blackford HillEdinburgh, EH9 3HJUnited KingdomTelephone: +44 (0)131668 8348E-mail: jkd@roe.ac.uk

Web: www.astro-opticon.org

Contacts

OPTICON - The Optical Infrared Coordination Network for Astronomy

JRA-6. VPHGs

OPTICON is funded by the European Commission under Contract RII3-CT-2004-001566

JRA 6 gathers together an inter-disciplinary group of scientists covering astronomy (ESO, IAC, INAF), material science (Politecnico di Milano) and VPHG manufacturers (CSL-Athol Liege). It aims to achieve a breakthrough in the application of VPHGs for astronomical instrumentation. Currently, use of VPHGs in existing instruments is limited and only partially exploits their remarkable capabilities. Moreover improvements are possible at the manufacturing level which will make VPHGs more suitable for specific applications. The JRA team will explore VPHG technology and provide the community with tested VPHG applications.VPHGs

VPHG are high diffraction efficiency transmission gratings. The diffraction is created by a layer of photo-sensitive material in which a sinusoidal pattern of refraction index is recorded via holography.

IR Laboratory prototypes set

The layer is embedded in glass plates that can be easily handled, cleaned and AR-coated. Up to 98% peak efficiency has been obtained at dispersion regimes in where surface relief gratings barely reach 50 %.

Tens of VPHGs are currently used by astronomers as they are progressively replacing grisms in low resolution spectrographs. New instruments are currently designed with VPHGs in mind

First VPHG-bases laboratory-grade UV cross-disperser

Dichromated Gelatine (DCG) is widely used but various families of polymers under study could outperform DCG.

The Activity

JRA-6 aims to provide, over its 5 year programme, science grade VPHG prototypes. Laboratory grade prototypes for each of the leading items have already been produced and are currently under testing.

First VPHG-bases Tunable Filter and preliminary results

Crucial parameters are the diffraction efficiency, a good transmitted wavefront, a high reproducibility and a reasonable cost

Diffraction Efficiency of an IR prototype

The JRA 6 team is continuing with development in order to obtain devices with higher performance and better characteristics. The next phase will have as its main driver real astronomical observations, possibly with Extremely Large Telescopes (ELTs)

Our Goal

a) IR VPHGs operated at cryogenic temperatures

b) UV VPHGs to be used as cross dispersers in high resolution spectrographs

c) Fully functional VPHG-based configurations, e.g. tunable filters, high resolution spectrographs

d) Real time re-writeable IR VPHGs based on photochromic polymers.

To provide fully functional science grade prototypes of: