Description
Spectrographs used for exoplanet characterisation often rely on highly stable Fabry-Perot interferometers for real time calibration. Designers of Fabry-Perot calibration systems commonly use modified Airy functions to model changes to mirror coatings, surface irregularities, and other sources of phase shift to identify and characterise sources of mode drift. Physical calibration systems have multiple sources of aberrations and non-ideal component structure causing etalon modes to change in shape, phase shift and vary in total transmission. This makes analytical etalon modelling and analysis limited in precision. This project utilises a physical optics propagation system to numerically determine the combined impact of aberrations both inside and outside of an etalon cavity. System aberration sources are categorised into external cavity, interacting and non-interacting internal cavity phase shift sources to optimise simulation completion speed. The impact of input beam shape, aperture, intensity and uniformity are accounted for within input and propagation spatial grids. Height maps are calculated for both simulated and experimentally measured mirror surfaces to account for surface roughness, surface figure and curvature. These height maps are then used to determine the phase shift due to optical path difference for light propagating within an etalon cavity. The Transfer Matrix Method (TMM) based PyEtalon Python package is utilised to determine each etalon mirror’s complex Fresnel coefficients, allowing for internal reflections and transmission to be calculated at each round trip for light propagating within a cavity. The developed system has been utilised to simulate the impact of coating, surface and beam aberrations on etalon mode shape, phase and transmission. HPF, HARPS, MaroonX and other etalon based calibration system mirror designs have been evaluated with this tool set. The developed Graphical User Interface (GUI) and Python package will enable other research teams to examine the impact of system aberrations in their own etalon calibration system designs.
| I am the presenting author | Yes |
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