Characterization of a photon counting EMCCD for space-based high contrast imaging spectroscopy of extrasolar planets

TL;DR

This paper discusses the development and characterization of a photon counting EMCCD detector crucial for future space missions aimed at directly imaging and analyzing exoplanets, focusing on overcoming technical challenges like clock-induced charge.

Contribution

It presents progress in characterizing a low-noise EMCCD for space-based exoplanet spectroscopy, including solutions to charge trapping issues, demonstrating its suitability for high-contrast imaging.

Findings

Demonstrated photon counting capability with high gain register

Identified solutions to clock-induced charge problems

Validated detector performance for faint exoplanet signals

Abstract

We present the progress of characterization of a low-noise, photon counting Electron Multiplying Charged Coupled Device (EMCCD) operating in optical wavelengths and demonstrate possible solutions to the problems of Clock-Induced Charge (CIC) and other trapped charge through sub-bandgap illumination. Such a detector will be vital to the feasibility of future space-based direct imaging and spectroscopy missions for exoplanet characterization, and is scheduled to fly on-board the AFTA-WFIRST mission. The 512$\times$512 EMCCD is an e2v detector housed and clocked by a N\"uv\"u Cameras controller. Through a multiplication gain register, this detector produces as many as 5000 electrons for a single, incident-photon-induced photoelectron produced in the detector, enabling single photon counting operation with read noise and dark current orders of magnitude below that of standard CCDs. With the extremely high contrasts (Earth-to-Sun flux ratio is $\sim$ 10$^{-10}$) and extremely faint targets (an Earth analog would measure 28$^{th}$ - 30$^{th}$ magnitude or fainter), a photon-counting EMCCD is absolutely necessary to measure the signatures of habitability on an Earth-like exoplanet within the timescale of a mission's lifetime, and we discuss the concept of operations for an EMCCD making such measurements.