First on-sky results of a FIOS prototype, a Fabry Perot Based Instrument for Oxygen Searches

The upcoming Extremely Large Telescopes (ELTs) are expected to have the collecting area required to detect potential biosignature gases such as molecular oxygen, $\mathrm{O_2}$, in the atmosphere of terrestrial planets around nearby stars. One of the most promising detection methods is transmission spectroscopy. To maximize our capability to detect $\mathrm{O_2}$ using this method, spectral resolutions $\mathrm{R}\geq 300,000$ are required to fully resolve the absorption lines in an Earth-like exoplanet atmosphere and disentangle the signal from telluric lines. Current high-resolution spectrographs typically achieve a spectral resolution of $\mathrm{R}\sim100,000$. Increasing the resolution in seeing limited observations/instruments requires drastically larger optical components, making these instruments even more expensive and hard to fabricate and assemble. Instead, we demonstrate a new approach to high-resolution spectroscopy. We implemented an ultra-high spectral resolution booster to be coupled in front of a high-resolution spectrograph. The instrument is based on a chained Fabry Perot array which generates a hyperfine spectral profile. We present on-sky telluric observations with a lab demonstrator. Depending on the configuration, this two-arm prototype reaches a resolution of R=250,000-350,000. After carefully modeling the prototype's behavior, we propose a Fabry Perot Interferometer (FPI) design for an eight-arm array configuration aimed at ELTs capable of exceeding R=300,000. The novel FPI resolution booster can be plugged in at the front end of an existing R=100,000 spectrograph to overwrite the spectral profile with a higher resolution for exoplanet atmosphere studies.