Characterisation of cooled infrared fibres for the Gemini IRMOS

Recently integral field spectroscopy has become a band-wagon among the optical astronomical community and most of the 8m class telescopes plan to offer this as part of their instrumentation package. The possibility of expanding integral field spectroscopy into the near infrared (1-2.5μm) opens exciting new possibilities for the study of a variety of astronomical objects. In this paper, we discuss some of the design requirements for the proposed Gemini Infra-Red Multi-Object Spectrograph (GIRMOS) and sky subtraction techniques suitable for infrared fibre spectroscopy. We address the performance of optical fibres suitable for use from 1-2.5μm and the effects of cooling these fibres to liquid nitrogen temperatures (~77°K) including: focal ratio degradation (FRD), fibre transmission and thermal emissivity, mechanical properties and durability. Also discussed are issues related to sky subtraction for IR fibre spectroscopy such as: dedicated sky fibres, dedicated sky d-IFUs, and various beam switching methods. This work is all part of a development study for multiple deployable integral field units (d-IFUs) for GIRMOS.