Near-infrared metrology of high-performance silicon immersion gratings

Michael Gully-Santiago; Weisong Wang; Casey Deen; Daniel Jaffe

doi:10.1117/12.926434

13 September 2012 Near-infrared metrology of high-performance silicon immersion gratings

Michael Gully-Santiago, Weisong Wang, Casey Deen, Daniel Jaffe

Proceedings Volume 8450, Modern Technologies in Space- and Ground-based Telescopes and Instrumentation II; 84502S (2012) https://doi.org/10.1117/12.926434
Event: SPIE Astronomical Telescopes + Instrumentation, 2012, Amsterdam, Netherlands

Abstract

Silicon immersion gratings offer size and cost savings for high-resolution near-infrared spectrographs. The IGRINS instrument at McDonald Observatory will employ a high-performance silicon immersion echelle grating to achieve spectral resolution R = λ/Δλ40,000 simultaneously over H and K near-infrared band atmospheric windows (1.5-2.5 μm). We chronicle the metrology of an R3 silicon immersion echelle grating for IGRINS. The grating is 30x80 mm, etched into a monolithic silicon prism. Optical interferometry of the grating surface in reflection indicates high phase coherence (<λ/6 peak to valley surface error over a 25 mm beam at λ= 632 nm). Optical interferometry shows small periodic position errors of the grating grooves. These periodic errors manifest as spectroscopic ghosts. High dynamic range monochromatic spectral purity measurements reveal ghost levels relative to the main diffraction peak at 1.6x10^-3 at λ = 632 nm in reflection, consistent with the interferometric results Improved grating surfaces demonstrate reflection-measured ghosts at negligible levels of 10^-4 of the main diffraction peak. Relative on-blaze efficiency is ~75%. We investigate the immersion grating blaze efficiency performance over the entire operational bandwidth 1500 <λ(nm) < 2500 at room temperature. The projected performance at operational cryogenic temperatures meets the design specifications.

Citation Download Citation

Michael Gully-Santiago, Weisong Wang, Casey Deen, and Daniel Jaffe "Near-infrared metrology of high-performance silicon immersion gratings", Proc. SPIE 8450, Modern Technologies in Space- and Ground-based Telescopes and Instrumentation II, 84502S (13 September 2012); https://doi.org/10.1117/12.926434

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