Enhancing Direct Exoplanet Spectroscopy with Apodizing and Beam Shaping Optics

TL;DR

This paper introduces novel optical designs, including beam-shaping lenses and a grayscale apodizer, to enhance the signal-to-noise ratio in direct exoplanet spectroscopy, enabling more detailed atmospheric studies.

Contribution

It presents the design, fabrication, and laboratory testing of specialized optics that improve exoplanet signal detection and reduce stellar noise in high-resolution spectroscopy.

Findings

Optics increase S/N by ~33% in simulated observations.

Good agreement between theoretical and experimental PSFs.

Designs are effective for different noise regimes in exoplanet spectroscopy.

Abstract

Direct exoplanet spectroscopy aims to measure the spectrum of an exoplanet while simultaneously minimizing the light collected from its host star. Isolating the planet light from the starlight improves the signal-to-noise ratio (S/N) per spectral channel when noise due to the star dominates, which may enable new studies of the exoplanet atmosphere with unprecedented detail at high spectral resolution (>30,000). However, the optimal instrument design depends on the flux level from the planet and star compared to the noise due to other sources, such as detector noise and thermal background. Here we present the design, fabrication, and laboratory demonstration of specially-designed optics to improve the S/N in two potential regimes in direct exoplanet spectroscopy with adaptive optics instruments. The first is a pair of beam-shaping lenses that increase the planet signal by improving the coupling efficiency into a single-mode fiber at the known position of the planet. The second is a grayscale apodizer that reduces the diffracted starlight for planets at small angular separations from their host star. The former especially increases S/N when dominated by detector noise or thermal background, while the latter helps reduce stellar noise. We show good agreement between the theoretical and experimental point spread functions in each case and predict the exposure time reduction ($\sim 33\%$) that each set of optics provides in simulated observations of 51 Eridani b using the Keck Planet Imager and Characterizer instrument at W.M. Keck Observatory.