Characterization of a multi-etalon array for ultra-high resolution spectroscopy

The upcoming Extremely Large Telescopes (ELTs) are expected to have the collecting area required to detect potential biosignature gases in the atmosphere of rocky planets around nearby low-mass stars. Some efforts are currently focusing on searching for molecular oxygen (O2), since O2 is a known biosignature on Earth. One of the most promising methods to search for O2 is transmission spectroscopy in which high-resolution spectroscopy is combined with cross-correlation techniques. In this method, high spectral resolution is required both to resolve the exoplanet's O2 lines and to separate them from foreground telluric absorption. While current astronomical spectrographs typically achieve a spectral resolution of 100,000, recent studies show that resolutions of 300,000 -- 400,000 are optimal to detect O2 in the atmosphere of earth analogs with the ELTs. Fabry Perot Interferometer (FPI) arrays have been proposed as a relatively low-cost way to reach these resolutions. In this paper, we present performance results for our 2-FPI array lab prototype, which reaches a resolving power of 600,000. We further discuss the use of multi-cavity etalons (dualons) to be resolution boosters for existing spectrographs.