GPI 2.0: Exploring The Impact of Different Readout Modes on the Wavefront Sensor's EMCCD

TL;DR

This paper evaluates the performance of a specialized EMCCD detector in the upgraded GPI 2.0 instrument, demonstrating how different readout modes affect noise and linearity to optimize wavefront sensing for exoplanet imaging.

Contribution

It provides a detailed characterization of the EMCCD's performance in different readout modes, guiding optimal configuration for high-contrast imaging.

Findings

Switching to non-inverted mode improves charge diffusion.

Characterized noise sources like readout noise and dark current.

Assessed linearity and gain performance of the EMCCD.

Abstract

The Gemini Planet Imager (GPI) is a high contrast imaging instrument that aims to detect and characterize extrasolar planets. GPI is being upgraded to GPI 2.0, with several subsystems receiving a re-design to improve its contrast. To enable observations on fainter targets and increase performance on brighter ones, one of the upgrades is to the adaptive optics system. The current Shack-Hartmann wavefront sensor (WFS) is being replaced by a pyramid WFS with an low-noise electron multiplying CCD (EMCCD). EMCCDs are detectors capable of counting single photon events at high speed and high sensitivity. In this work, we characterize the performance of the HN\"u 240 EMCCD from N\"uv\"u Cameras, which was custom-built for GPI 2.0. Through our performance evaluation we found that the operating mode of the camera had to be changed from inverted-mode (IMO) to non-inverted mode (NIMO) in order to improve charge diffusion features found in the detector's images. Here, we characterize the EMCCD's noise contributors (readout noise, clock-induced charges, dark current) and linearity tests (EM gain, exposure time) before and after the switch to NIMO.