PRAXIS: a low background NIR spectrograph for fibre Bragg grating OH suppression

Anthony Horton; Simon Ellis; Jon Lawrence; Joss Bland-Hawthorn

doi:10.1117/12.924874

13 September 2012 PRAXIS: a low background NIR spectrograph for fibre Bragg grating OH suppression

Anthony Horton, Simon Ellis, Jon Lawrence, Joss Bland-Hawthorn

Proceedings Volume 8450, Modern Technologies in Space- and Ground-based Telescopes and Instrumentation II; 84501V (2012) https://doi.org/10.1117/12.924874
Event: SPIE Astronomical Telescopes + Instrumentation, 2012, Amsterdam, Netherlands

Abstract

Fibre Bragg grating (FBG) OH suppression is capable of greatly reducing the bright sky background seen by near infrared spectrographs. By filtering out the airglow emission lines at high resolution before the light enters the spectrograph this technique prevents scattering from the emission lines into interline regions, thereby reducing the background at all wavelengths. In order to take full advantage of this sky background reduction the spectrograph must have very low instrumental backgrounds so that it remains sky noise limited. Both simulations and real world experience with the prototype GNOSIS system show that existing spectrographs, designed for higher sky background levels, will be unable to fully exploit the sky background reduction. We therefore propose PRAXIS, a spectrograph optimised specifically for this purpose. The PRAXIS concept is a fibre fed, fully cryogenic, fixed format spectrograph for the J and H-bands. Dark current will be minimised by using the best of the latest generation of NIR detectors while thermal backgrounds will be reduced by the use of a cryogenic fibre slit. Optimised spectral formats and the use of high throughput volume phase holographic gratings will further enhance sensitivity. Our proposal is for a modular system, incorporating exchangeable fore-optics units, integral field units and OH suppression units, to allow PRAXIS to operate as a visitor instrument on any large telescope and enable new developments in FBG OH suppression to be incorporated as they become available. As a high performance fibre fed spectrograph PRAXIS could also serve as a testbed for other astrophotonic technologies.

Citation Download Citation

Anthony Horton, Simon Ellis, Jon Lawrence, and Joss Bland-Hawthorn "PRAXIS: a low background NIR spectrograph for fibre Bragg grating OH suppression", Proc. SPIE 8450, Modern Technologies in Space- and Ground-based Telescopes and Instrumentation II, 84501V (13 September 2012); https://doi.org/10.1117/12.924874

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