Tree rings in Large Synoptic Survey Telescope production sensors: Its dependence on radius, wavelength, and back bias voltage

Tree rings are one of the sensor effects that may affect precise measurements in the Large Synoptic Survey Telescope (LSST). The effect is caused by silicon wafer manufacturing process, resulting in formation of circular patterns due to variations of the silicon dopant concentration. We have analyzed flat-field images taken at Brookhaven National Laboratory and SLAC for all production sensors used to build the LSST camera in order to measure the amplitudes and periods of the tree ring patterns as a function of the radius, illumination wavelength, and sensor back bias voltage. With nominal back bias voltage settings, the tree ring amplitudes and periods for both ITL and e2v sensors are considered to have small impact on the galaxy shear measurement in LSST.