JRA-6. VPHGs

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JRA-6. VPHGs
To provide fully functional science grade
prototypes of
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 Di
chromated 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)
OPTICON is funded by the European Commission
under Contract RII3-CT-2004-001566