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The "brighter-fatter" (BF) effect is a phenomenon (originally discovered incharge coupled devices) in which the size of the detector point spread function(PSF) increases with brightness. We present, for the first time, laboratorymeasurements demonstrating the existence of the effect in a Hawaii-2RG HgCdTenear infrared (NIR) detector. We use the Precision Projector Laboratory, a JPLfacility for emulating astronomical observations with UV/VIS/NIR detectors, toproject about 17,000 point sources onto the detector to stimulate the effect.After calibrating the detector for nonlinearity with flat-fields, we findevidence that charge is nonlinearly shifted from bright pixels to neighboringpixels during exposures of point sources, consistent with the existence of aBF-type effect. The Wide Field Infrared Survey Telescope (WFIRST) by NASA willuse similar detectors to measure weak gravitational lensing from the shapes ofhundreds of million of galaxies in the NIR. The WFIRST PSF size must becalibrated to approximately 0.1 percent to avoid biased inferences of darkmatter and dark energy parameters; therefore further study and calibration ofthe BF effect in realistic images will be crucial.

Laboratory measurement of the brighter-fatter effect in an H2RG infrared detector