Multiple‐Object and Integral Field Near‐Infrared Spectroscopy Using Fibers

We describe a new system for multiple object spectroscopy and integral fieldspectroscopy at near-infrared wavelengths using optical fibers. Both modes ofthe SMIRFS instrument have been tested at the UK Infrared Telescope with theCGS4 infrared spectrograph. The modular system includes a common optical systemto image the fiber slit onto the cold slit inside the CGS4 cryostat. Themultiobject mode consists of 14 interchangeable fused silica or zirconiumfluoride fibers each with a field of 4 arcsec. The integral field mode consistsof 72 fused silica fibers coupled with a lenslet array to give a contiguousfield of 6x4 arcsec with 0.6 arcsec sampling. We describe the performance of both modes. For the multiobject mode, thefeasibility and desirability of using fluoride fibers to extend the wavelengthrange into the K-band is discussed. For the integral field mode, theperformance is compared with theoretical expectation with particular attentionto the effect of Focal Ratio Degradation in the fibers. These results demonstrate the feasibility of multiobject and integral fieldspectroscopy in the near-infrared using lenslet-coupled fiber systems. AlthoughSMIRFS in an experimental system working with a spectrograph not designed forthis purpose, the throughput and uniformity of response are good. SMIRFS pointsthe way forward to systems with much larger numbers of elements.