Design for the COBE far-infrared absolute spectrophotometer

1 October 1993

proceedings article
Published by SPIE-Intl Soc Optical Eng

Vol. 2019, 168-180
https://doi.org/10.1117/12.157823

Abstract

The Far InfraRed Absolute Spectrophotometer (FIRAS) was built to measure the spectrum of diffuse emission from 1 to 100 cm^-1, with particular attention to possible differences between the spectrum of the cosmic microwave background radiation (CMBR) and a blackbody spectrum as small as 0.1% of the peak of the CMBR spectrum. The FIRAS has differential inputs and outputs, a full beam external calibrator, a controllable reference blackbody, and a polarizing Michelson interferometer with bolometer detectors. It is operated at a temperature of 1.5 K inside a liquid helium cryostat to suppress instrument emission and improve detector sensitivities. It has an intrinsic frequency resolution of the order of 0.7%, maximum path lengths of 1.2 and 5.9 cm, and a beamwidth of 7 degree(s), and achieved its goals for accuracy and rms sensitivity for νI_ν, which are better than 10^-9 W/cm²sr over the frequency range from 2 to 20 cm^-1.

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