Infrared fibres in astronomical instrumentation

Abstract

For several years multi-object spectroscopy systems have been available for carrying out survey work in the visible region, but until very recently there has not been a system for the near infrared region. This thesis describes the design, manufacture and commissioning of the first multi-object fibre system for near infrared spectroscopy. SMIRFS (Spectroscopic Multi-object Infrared Fibre System) is a prototype system that has been designed at the Department of Physics in Durham to couple the Cassegrain focus of the United Kingdom InfraRed Telescope (UKIRT) to a cooled long slit infrared spectrograph (CGS4). Two different fibre bundles are available, each containing 14 fibres. One bundle is made from zirconium fluoride fibres, for K band spectroscopy and the second bundle is made from silica fibres, for J and H band spectroscopy. During the design process of SMIRFS a number of issues were addressed. These included; the characteristics of infrared fibres, in particular their throughput and FRD, atmospheric features in the near infra-red and suitable sky subtraction techniques, fibre preparation and evaluation, the use of microlenses for coupling slow focal ratio beams with fibres, and the thermal emissions from the warm material of the instrument. These, along with the design, manufacture and testing of the SMIRFS are described in detail, including the fibre evaluation results and estimates for throughput, instrument thermal background derived from the commissioning run data. Finally, there is a brief discussion on the development of infrared fibre system for astronomy.