A novel laser-alignment system for tracking detectors using transparent silicon strip sensors

Modern large-area precision tracking detectors require increasing accuracy for the alignment of their components. A novel multi-point laser-alignment system has been developed for such applications, in particular for the muon spectrometer of the ATLAS detector at the Large Hadron Collider. The position of the detector components is monitored with respect to reference laser beams using semitransparent optical position sensors at multiple consecutive stations. The custom designed sensors work on the principle of silicon strip photodiodes. Two types of transparent strip sensors, based on crystalline and on amorphous silicon as active material, have been studied. The sensors provide two-dimensional position measurement with order 1 mu m resolution uniformly over a transverse range of several centimeters. Light transmission rates of > 90% have been achieved at selected wavelengths using laser diodes. This will enable us to place more than 10 sensors along one laser beam. Custom-designed integrated readout electronics is being developed for the sensor systems.