Optical Design and Performance of the Planetary Fourier Spectrometer (PFS)

Abstract

The Planetary Fourier Spectrometer (PFS) is a two-channel Michelson interferometer operating in the IR from 1.25 to 45 mu m. Two retroreflectors are mounted on brackets that are at an angle of 90 degrees and fixed on an axle driven by a torque motor. The angular movement of the retroreflectors relative to the beam-splitter generates the optical path difference. The two primary degrees and the one secondary degree of freedom for misalignment are derived. The pattern of interference fringes, typical for the different types of misalignment, will be simulated, and their use for alignment will be demonstrated. This interferometer design is very robust towards slight misalignment in harsh environments, compared to the classical Michelson-type interferometer. This favours the design for applications in space. The PFS is intended for the mission Mars '96. It is optimised for the study of the Martian atmosphere. The spectra will also be used for investigations of the Martian soil.