Silicon immersion gratings and their spectroscopic applications

摘要

Silicon immersion gratings (SIGs) offer several advantages over the commercial echelle gratings for highresolution infrared (IR) spectroscopy: 3.4 times the gain in dispersion or ~10 times the reduction in theinstrument volume, a multiplex gain for a large continuous wavelength coverage and low cost. Wepresent results from lab characterization of a large format SIG of astronomical observation quality. ThisSIG, with a 54.74 degree blaze angle (R1.4), 16.1 l/mm groove density, and 50x86 mmsup2/sup grating area, wasdeveloped for high resolution IR spectroscopy (R~70,000) in the near IR (1.1-2.5 μm). Its entrancesurface was coated with a single layer of silicon nitride antireflection (AR) coating and its grating surfacewas coated with a thin layer of gold to increase its throughput at 1.1-2.5 ?m. The lab measurements haveshown that the SIG delivered a spectral resolution of R=114,000 at 1.55 ?m with a lab testingspectrograph with a 20 mm diameter pupil. The measured peak grating efficiency is 72% at 1.55 ?m,which is consistent with the measurements in the optical wavelengths from the grating surface at the airside. This SIG is being implemented in a new generation cryogenic IR spectrograph, called the Florida IRSilicon immersion grating spectrometer (FIRST), to offer broad-band high resolution IR spectroscopywith R=72,000 at 1.4-1.8 um under a typical seeing condition in a single exposure with a 2kx2k H2RG IRarray at the robotically controlled Tennessee State University 2-meter Automatic Spectroscopic Telescope(AST) at Fairborn Observatory in Arizona. FIRST is designed to provide high precision Dopplermeasurements (~4 m/s) for the identification and characterization of extrasolar planets, especially rockyplanets in habitable zones, orbiting low mass M dwarf stars. It will also be used for other high resolutionIR spectroscopic observations of such as young stars, brown dwarfs, magnetic fields, star formation andinterstellar mediums. An optimally designed SIG of the similar size can be used in the Silicon ImmersionGrating Spectrometer (SIGS) to fill the need for high resolution spectroscopy at mid IR to far IR (~25-300 μm) for the NASA SOFIA airborne mission in the future.© (2012) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.