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Proceedings Paper

Development of silicon grisms and immersion gratings for high-resolution infrared spectroscopy
Author(s): Jian Ge; Daniel Ludlow McDavitt; John Luther Bernecker; Shane Miller; Dino R. Ciarlo; Paul J. Kuzmenko
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Paper Abstract

We report new results on silicon grism and immersion grating development using photolithography and anisotropic chemical etching techniques, which include process recipe finding, prototype grism fabrication, lab performance evaluation and initial scientific observations. The very high refractive index of silicon (n=3.4) enables much higher dispersion power for silicon-based gratings than conventional gratings, e.g. a silicon immersion grating can offer a factor of 3.4 times the dispersion of a conventional immersion grating. Good transmission in the infrared (IR) allows silicon-based gratings to operate in the broad IR wavelength regions (~1- 10 micrometers and far-IR), which make them attractive for both ground and space-based spectroscopic observations. Coarser gratings can be fabricated with these new techniques rather than conventional techniques, allowing observations at very high dispersion orders for larger simultaneous wavelength coverage. We have found new etching techniques for fabricating high quality silicon grisms with low wavefront distortion, low scattered light and high efficiency. Particularly, a new etching process using tetramethyl ammonium hydroxide (TMAH) is significantly simplifying the fabrication process on large, thick silicon substrates, while providing comparable grating quality to our traditional potassium hydroxide (KOH) process. This technique is being used for fabricating inch size silicon grisms for several IR instruments and is planned to be used for fabricating ~ 4 inch size silicon immersion gratings later. We have obtained complete K band spectra of a total of 6 T Tauri and Ae/Be stars and their close companions at a spectral resolution of R ~ 5000 using a silicon echelle grism with a 5 mm pupil diameter at the Lick 3m telescope. These results represent the first scientific observations conducted by the high-resolution silicon grisms, and demonstrate the extremely high dispersing power of silicon- based gratings. The future of silicon-based grating applications in ground and space-based IR instruments is promising. Silicon immersion gratings will make very high-resolution spectroscopy (R>100,000) feasible with compact instruments for implementation on large telescopes. Silicon grisms will offer an efficient way to implement low-cost medium to high resolution IR spectroscopy (R~ 1000-50000) through the conversion of existing cameras into spectrometers by locating a grism in the instrument's pupil location.

Paper Details

Date Published: 30 January 2002
PDF: 12 pages
Proc. SPIE 4485, Optical Spectroscopic Techniques, Remote Sensing, and Instrumentation for Atmospheric and Space Research IV, (30 January 2002); doi: 10.1117/12.454275
Show Author Affiliations
Jian Ge, The Pennsylvania State Univ. (United States)
Daniel Ludlow McDavitt, The Pennsylvania State Univ. (United States)
John Luther Bernecker, The Pennsylvania State Univ. (United States)
Shane Miller, The Pennsylvania State Univ. (United States)
Dino R. Ciarlo, Lawrence Livermore National Lab. (United States)
Paul J. Kuzmenko, Lawrence Livermore National Lab. (United States)

Published in SPIE Proceedings Vol. 4485:
Optical Spectroscopic Techniques, Remote Sensing, and Instrumentation for Atmospheric and Space Research IV
Allen M. Larar; Martin G. Mlynczak, Editor(s)

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