Interferometer with single-axis robot: design, alignment and performance

Abstract

An interferometer is an essential subsystem of the Fourier-transform spectrometer (FTS). We describe an FTS instrument to operate at the surface of Mars based on a Michelson interferometer with hollow retroreflectors. The instrument will operate in two different regimes, observing the solar disc through the atmosphere to measure trace gases, and measuring the thermal emission from the atmosphere to study the planetary boundary layer (PBL). The interferometer has an aperture of 1 inch, operates in the spectral range 1.7-17 μm, and features low mass and volume (≤1 kg with all necessary subsystems). Beam splitter and compensator are made of potassium bromide (KBr). A single-axis robot with stepper motor drive provides a linear movement of the retroreflector (the speed stability is about 2%) and enables a maximal optical path difference (MOPD) of 15 cm. A reference channel with a distributed-feedback laser diode (0.76 μm) and a photodiode (Si) supports the interferogram sampling and the speed stabilization loop. The time to measure one interferogram with a best spectral resolution of about 0.05 cm-1 is 500 s (the sun tracking regime). In the thermal sounding regime, one measurement of a two-side interferogram (with the spectral resolution of ~1 cm-1) takes less than 1 min. Laboratory calibrations with a black body and a laser confirm the design parameters of the instrument.

Scientific Instrumentation Complex for the ExoMars-2022 Landing Platform

“…To carry out these measurements, it was necessary to ensure the simultaneous operation of two optical-mechanical precision systems. One maintained tracking of the solar disk during a long-term observation (Shakun et al, 2019a), another supported the smooth movement of the carriage with the interferometer mirror (Shakun et al, 2019b). In laboratory observations of the Sun at maximum spectral resolution, a relatively low signal-to-noise ratio of ~30, was obtained, however, sufficient for measuring the known small components of the atmosphere (H 2 O, CO, O 3 ) or large methane emissions.…”

“…The instrument was developed and manufactured at IKI RAS, partly based on technical solutions of the TIRVIM Fourier spectrometer, one of the channels of the ACS spectroscopic complex on the ExoMars-2016 orbiter (Korablev et al, 2018;Shakun et al, 2018). Unfortunately, there is no generalizing publication on the FAST instrument yet; some information can be found in (Shakun et al, 2017(Shakun et al, , 2019a(Shakun et al, , 2019b.…”

Martian surface-atmosphere properties obtained with ExoMars infrared instrument TIRVIM and HP3 on InSight

“…The infrared-transform spectrometer FAST (Fourier for Atmospheric Species and Temperature) experiment, which will operate on the ExoMars 2022 platform, will play a prominent role at this. The interferometer has an aperture of about 2.5 cm and operates in the spectral range between 1.7 and 17 µm with a best spectral resolution of about 0.05 cm -1 in the Sun tracking mode (Shakun et al, 2019 14 ; Zelenyi et al, 2015 15 ). The instrument is aimed at long-term thermal sounding of the Martian atmosphere and retrieval of the aerosol properties (dust and ice) as well as measurements of minor species by observing the Sun from the surface.…”