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Weak gravitational lensing observations are a key science driver for the NASAWide Field Infrared Survey Telescope (WFIRST). To validate the performance ofthe WFIRST infrared detectors, we have performed a laboratory emulation of weakgravitational lensing measurements. Our experiments used a custom precisionprojector system to image a target mask composed of a grid of pinholes,emulating stellar point sources, onto a 1.7 micron cut-off Teledyne HgCdTe/H2RGdetector. We used a 880nm LED illumination source and f/22 pupil stop toproduce undersampled point spread functions similar to those expected fromWFIRST. We also emulated the WFIRST image reconstruction strategy, using theIMage COMbination (IMCOM) algorithm to derive oversampled images from dithered,undersampled input images. We created shear maps for this data and computedshear correlation functions to mimic a real weak lensing analysis. Afterremoving only 2nd order polynomial fits to the shear maps, we found that thecorrelation functions could be reduced to O(10^-6). This places a conservativeupper limit on the detector-induced bias to the correlation function (under ourtest conditions). This bias is two orders of magnitude lower than the expectedweak lensing signal. Restricted to scales relevant to dark energy analyses (skyseparations > 0.5 arcmin), the bias is O(10^-7): comparable to the requirementfor future weak lensing missions to avoid biasing cosmological parameterestimates. Our experiment will need to be upgraded and repeated under differentconfigurations to fully characterize the shape measurement performance ofWFIRST IR detectors.

Initial results from a laboratory emulation of weak gravitational lensing measurements