Calibration of the MIRI instrument on the James Webb Space Telescope and MIRI exoplanet spectroscopy

The James Webb Space Telescope (JWST) will detect faint heat signatures emitted from faraway celestial objects. The further the object, the longer it takes for the emitted light to reach us. Visible light that was once emitted from the first galaxies formed after the Big Bang gets red-shifted on its way here. Only a very sensitive infrared instrument may detect it. The water in the Earth's atmosphere blocks infrared light from reaching the surface, hence JWST will be sent to space, where its scientific instruments will be able to detect the light from faraway galaxies, as well as nearby exoplanet-hosting solar systems, and objects in our own solar system.

The Mid-Infrared Instrument (MIRI) on-board JWST will provide imaging, coronagraphy, low-resolution spectroscopy and medium-resolution spectroscopy at unprecedented sensitivity levels in the 5 to 28 micron wavelength range. MIRI uses Si:As impurity band conduction detector arrays to detect infrared light. This type of detector was used in numerous past space missions, including the Infrared Space Observatory and the Spitzer Space Telescope. MIRI builds upon their legacy.

The aim of this thesis is to make use of data acquired with MIRI in multiple ground-based test campaigns to characterize and model instrument properties that allow to calibrate and process raw MIRI detector signals to calibrated spectra and spectral cubes. The calibration methods developed in this thesis are applicable to past, present, and future mid-infrared instruments.

We open this thesis with an introduction to the JWST mission, the JWST science goals, and the technical specifications of the instruments on-board JWST. We then focus on MIRI. We describe the MIRI raw data format and describe how a photon incident to the MIRI detectors gets turned into a digital signal at the amplifier output. Thereafter we focus on the MIRI medium-resolution integral field spectrometer (MRS). Optical distortions, optical transmission effects, and thermal effects impact the calibration of the MRS. Throughout the thesis we critically evaluate past methods to calibrate the MIRI instrumental effects and present novel calibration methods to improve science with MIRI and the MRS.