Automatic tracking of the intersection of a laser and electron beam

For the Compton Polarimeter Experiment at the Stanford Linear Accelerator, the crossing point of a laser beam and an electron beam must be kept accurate and stable. An electronic system is described for the automatic tracking and correcting of the beam crossing. A remote CCD (charge-coupled device) camera, relatively insensitive to electromagnetic disturbance, records small displacements of the pulsed laser beam. Video signals are analyzed at a remote station, the amount of drift from a selected reference point is determined, and the appropriate correction commands are sent to the motorized mirror deflecting the laser beam. The electronic circuits for laser beam control were built and tested in a laboratory setup. The system was also tested under pulsed-light conditions resembling those expected in the Compton Polarimeter Experiment