Maturing electron multiplying charge coupled device photon-counting with variable multiplication gain imaging for a coronagraphic instrument

This is an introduction to a US government program that conducted high-contrast imaging experiments with an electron multiplying charge coupled device (EMCCD) in an interferometric coronagraph. This report will introduce the concepts of “charge blooming” and “starlight saturation” in the context of high-contrast astronomical imaging. These phenomena adversely effect the performance of high-contrast photon-counting instruments that do not use a mask to physically block starlight in the science channel of the coronagraph. The problems will be presented with the help of images taken with a commercial EMCCD camera in the visible nulling coronagraph at the Goddard Space Flight Center. A new clocking scheme for EMCCDs—variable multiplication gain clocking—will be proposed as a means for suppressing horizontal blooming and starlight saturation in an astronomical camera. This opening report will conclude with a discussion of design considerations for a new controller for high-contrast photon-counting with an EMCCD in a coronagraphic instrument. This controller will allow a single frame from an EMCCD to be scanned in multiple modes—photon-counting and digitization—with a variable multiplication gain clock to enable direct imaging of an exoplanet and wavefront control of a coronagraph, simultaneously.