Infrared laser testing of ALICE silicon pixel detector assemblies

The Silicon Pixel Detector (SPD) comprises the two innermost layers of the ALICE Inner Tracker System (ITS). The SPD is based on hybrid pixels and is designed to provide precise position determination in the high track density region close to the interaction point. The SPD consists of 9.8×1069.8×106 pixel cells of dimensions 50μm(rφ)×425μm(z). Each of the 1200 chips contains a matrix of 8192 pixel cells. A test system has been developed based on a 1060 nm diode laser in order to study single assemblies with an opening in the aluminum back side contact of the sensor. The test system has been used to investigate the charge sharing in adjacent pixels. The results are compared with those from recent measurements in high-energy particle beams.