PRAXIS: an OH suppression optimised near infrared spectrograph

S. C. Ellis*, S. Bauer, C. Bacigalupo, J. Bland-Hawthorn, J. J. Bryant, S. Case, R. Content, T. Fechner, D. Giannone, R. Haynes, E. Hernandez, A. J. Horton, U. Klauser, J. S. Lawrence, S. G. Leon-Saval, E. Lindley, H. G. Löhmannsröben, S. S. Min, N. Pai, M. RothK. Shortridge, L. Waller, Pascal Xavier, Ross Zhelem

*Corresponding author for this work

Research output: Chapter in Book/Report/Conference proceedingConference proceeding contributionpeer-review

9 Citations (Scopus)


The problem of atmospheric emission from OH molecules is a long standing problem for near-infrared astronomy. PRAXIS is a unique spectrograph which is fed by fibres that remove the OH background and is optimised specifically to benefit from OH-Suppression. The OH suppression is achieved with fibre Bragg gratings, which were tested successfully on the GNOSIS instrument. PRAXIS uses the same fibre Bragg gratings as GNOSIS in its first implementation, and will exploit new, cheaper and more efficient, multicore fibre Bragg gratings in the second implementation. The OH lines are suppressed by a factor of ∼ 1000, and the expected increase in the signal-to-noise in the interline regions compared to GNOSIS is a factor of ∼ 9 with the GNOSIS gratings and a factor of ∼ 17 with the new gratings. PRAXIS will enable the full exploitation of OH suppression for the first time, which was not achieved by GNOSIS (a retrofit to an existing instrument that was not OH-Suppression optimised) due to high thermal emission, low spectrograph transmission and detector noise. PRAXIS has extremely low thermal emission, through the cooling of all significantly emitting parts, including the fore-optics, the fibre Bragg gratings, a long length of fibre, and the fibre slit, and an optical design that minimises leaks of thermal emission from outside the spectrograph. PRAXIS has low detector noise through the use of a Hawaii-2RG detector, and a high throughput through a efficient VPH based spectrograph. PRAXIS will determine the absolute level of the interline continuum and enable observations of individual objects via an IFU. In this paper we give a status update and report on acceptance tests.

Original languageEnglish
Title of host publicationGround-based and Airborne Instrumentation for Astronomy VII
EditorsChristopher J. Evans, Luc Simard, Hideki Takami
Place of PublicationBellingham, Washington
Number of pages16
ISBN (Electronic)9781510619586
ISBN (Print)9781510619579
Publication statusPublished - 6 Jul 2018
EventGround-based and Airborne Instrumentation for Astronomy VII 2018 - Austin, United States
Duration: 10 Jun 201814 Jun 2018

Publication series

NameProceedings of SPIE
ISSN (Print)0277-786X
ISSN (Electronic)1996-756X


ConferenceGround-based and Airborne Instrumentation for Astronomy VII 2018
Country/TerritoryUnited States


  • astrophotonics
  • fibre Bragg gratings
  • Near infrared
  • OH suppression
  • spectroscopy


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