Fabrication of Pupil Masks for a New Infrared Exoplanet Imager at Keck Observatory

TL;DR

This paper details the design, simulation, and evaluation of pupil masks, including cold stops and Lyot stops, for the SCALES infrared exoplanet imager at Keck Observatory, focusing on starlight suppression and thermal background reduction.

Contribution

It introduces optimized geometric masks and analyzes their performance through simulations, considering manufacturing tolerances and optical alignments.

Findings

Optimized cold stop and Lyot stop designs improve starlight suppression.

Simulations demonstrate effective performance in K, L, and M bands.

Manufacturing tolerances and tilt effects are quantified and addressed.

Abstract

The Slicer Combined with Array of Lenslets for Exoplanet Spectroscopy (SCALES) is an instrument being designed to perform direct imaging of exoplanets in the mid-infrared (2-5 {\mu}m) with the Adaptive Optics System of W.M. Keck Observatory. To eliminate unwanted thermal infrared radiation, SCALES utilizes both a cold stop for excluding background radiation and a vector vortex coronagraph with Lyot stops for starlight suppression. Optimal geometric masks have been designed. We simulate the propagation of light through the Lyot plane and analyze the on-axis images of stars in the K, L, and M band for the performance of the Lyot stops. Additionally, finalized cold stop and Lyot stop designs are presented along with evaluations on the effects of manufacturing tolerances and tilt in pupil planes caused by off-axis parabolic mirror relays.