We have recently completed a set of silicon grisms for JWST-NIRCam. These devices have exquisite optical characteristics: phase surfaces flat to λ/100 peak to valley at the blaze wavlength, diffraction-limited PSFs down to 10^-5 of the peak, low scattered light levels, and large resolving-power slit-width products for their width and thickness. The one possible drawback to these devices is the large Fresnel loss caused by the large refractive index of Si. We report here on throughput and phase-surface measurements for a sample grating with a high performance antireflection coating on both the flat and grooved surfaces. These results indicate that we can achieve very high on-blaze efficiencies. The high throughput should make Si grisms an attractive dispersive element for moderate resolution IR spectroscopy in both ground and space based instruments throughout the 1.2-8 μm spectral region.

Date Published: 20 July 2010
PDF: 7 pages
Proc. SPIE 7739, Modern Technologies in Space- and Ground-based Telescopes and Instrumentation, 77393S (20 July 2010); doi: 10.1117/12.857568

Published in SPIE Proceedings Vol. 7739:
Modern Technologies in Space- and Ground-based Telescopes and Instrumentation
Eli Atad-Ettedgui; Dietrich Lemke, Editor(s)