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

摘要

We present the progress of characterization of a low-noise, photon countingElectron Multiplying Charged Coupled Device (EMCCD) operating in opticalwavelengths and demonstrate possible solutions to the problems of Clock-InducedCharge (CIC) and other trapped charge through sub-bandgap illumination. Such adetector will be vital to the feasibility of future space-based direct imagingand spectroscopy missions for exoplanet characterization, and is scheduled tofly on-board the AFTA-WFIRST mission. The 512$\times$512 EMCCD is an e2vdetector housed and clocked by a N\"uv\"u Cameras controller. Through amultiplication gain register, this detector produces as many as 5000 electronsfor a single, incident-photon-induced photoelectron produced in the detector,enabling single photon counting operation with read noise and dark currentorders of magnitude below that of standard CCDs. With the extremely highcontrasts (Earth-to-Sun flux ratio is $\sim$ 10$^{-10}$) and extremely fainttargets (an Earth analog would measure 28$^{th}$ - 30$^{th}$ magnitude orfainter), a photon-counting EMCCD is absolutely necessary to measure thesignatures of habitability on an Earth-like exoplanet within the timescale of amission's lifetime, and we discuss the concept of operations for an EMCCDmaking such measurements.