The calibration and monitoring system for the PHENIX lead-scintillator electromagnetic calorimeter

The calibration and monitoring system for the PHENIX lead-scintillator electromagnetic calorimeter is described along with the experience obtained in using this system to calibrate calorimeter modules with cosmic rays. The system is based on a UV laser which delivers light to each module through a series of optical fibers and splitters that is monitored at various points using silicon and vacuum photodiodes. Results are given from a prototype system based on a nitrogen laser which was used to monitor the stability of several modules, as well as to set the gains of the phototubes and establish the energy calibration of all calorimeter modules before installation into the final detector. A description of the final system to be used in PHENIX, based on a high power YAG laser, is also given.