AAS 203rd Meeting, January 2004
Session 38 Observation and Instrumentation : Optical
Poster, Tuesday, January 6, 2004, 9:20am-6:30pm, Grand Hall

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[38.09] High Quality TMAH Etched Silicon Echelle Gratings ready for Astronomical Spectroscopy

D. McDavitt, J. Wang, J. Ge, S. Miller (Penn State)

We report new testing results for infrared silicon diffraction gratings, showing that a new etching process using tetramethyl ammonium hydroxide (TMAH) can fabricate high quality gratings with both fine and coarse grooves (5-200 \mum groove size). We have modeled the diffraction efficiencies of one 13\mum reflection grating sample with the commercially available Grating SOLVER (GSOLVER 4.20) software, and measured the diffraction efficiencies with 64% at \lambda=543.5 nm and 45% at \lambda=632.8 nm in a Littrow mounting, which match the modeling curves well within the 1% error bar. The integrated scattered light level is less than 1%. To fully construct the blaze function, we set up an echelle spectrograph with a low dispersion grating as a cross-disperser. We obtained an echelle spectrum with a continuum source and then calibrated the wavelength with a Neon emission lamp. The resolving power of an etched grating with a 10 mm collimated beam is R = 11000, indicating a diffraction-limited performance. The blaze function also matches the theoretical efficiency curve. From these recent testing results, we conclude that the silicon gratings we fabricated with our anisotropic etching technique can satisfy the quality requirements for high resolution astronomical spectrographs in both the visible and near IR.

This work was supported by NASA grants NGA5-12115, NAG5-11427, NSF AST-0138235 and the Penn State Eberly College of Science.

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