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.