ALMA Memo #275

Analysis of Reflective Gratings as Infrared Filters

W. Grammer [1]

October 4, 1999

Keywords: grating, infrared filter, analysis

Reflective diffraction gratings are investigated for use as infrared filters in submillimeter-wave cryogenic receivers, to reduce radiative loading via the dewar window on the 4K stage. The grating diffracts incident IR away from the signal path, back toward the window. Analysis using scalar approximations indicate a single grating filter blocks close to 98% of the incident IR at 300K along the RF signal path, assuming a 20 (15 ) RMS surface deviation and 45 degree incidence. With a blazed grating profile, the filter rejection was found to depend only on the RMS surface deviation and incident angle.

[1] NRAO/TUC

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Last modified: 05 October, 1999