  The "crosshatch" pattern is a recurring "feature" of HgCdTe arrays,
specifically the Teledyne HAWAII family of near infrared detectors. It is a
fixed pattern of high frequency QE variations along 3 directions generally
thought to be related to the crystal structure of HgCdTe. The pattern is
evident in detectors used in Hubble WFC3, WISE, JWST, and in candidate
detectors for Euclid and WFIRST. Using undersampled point sources projected
onto a HAWAII-2RG detector, we show that the pattern induces photometric
variations that are not removed by a flat-field calibration, thus demonstrating
that the QE variations occur on scales smaller than the 18 micron pixels. Our
testbed is the Precision Projector Laboratory's astronomical scene generator,
which can rapidly characterize the full detector by scanning thousands of
undersampled spots. If not properly calibrated, detectors showing strong
crosshatch may induce correlated errors in photometry, astrometry,
spectroscopy, and shape measurements.
