A test of the laser alignment system ALMY at the TTF-FEL

The laser alignment system ALMY was tested at the 15 m long undulator section of the TESLA test facility. The positions of the undulator modules relative to each other have been determined with a precision of 0.1 mm, limited by the accuracy of the mechanical support of the sensors. Additionally, ALMY allows one to measure movements or drifts over several days and we found that the undulator components are stable within 10 μm. The resolution of the sensors is better than 2 μm over a distance of 15 m.