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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
the instrument's contrast. To enable observations on fainter targets and increase stability 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 HNu 240 EMCCD from Nuvu Cameras, which was custom-built for GPI 2.0. The HNu
240 EMCCD's characteristics make it well suited for extreme AO: it has low dark current (< 0.01 e-/pix/fr),
low readout noise (0.1 e-/pix/fr at a gain of 5000), high quantum efficiency ( 90% at wavelengths from 600-800
nm; 70% from 800-900 nm), and fast readout (up to 3000 fps full frame). Here we present test results on the
EMCCD's noise contributors, such as the readout noise, pixel-to-pixel variability and CCD bias. We also tested
the linearity and EM gain calibration of the detector. All camera tests were conducted before its integration into
the GPI 2.0 PWFS system.
