A Diode-Pumped DP2-447 Blue Laser for Monitoring CMS Lead Tungstate Crystals Calorimeter at the LHC

Monitoring the changes in channel response is crucial to maintain the energy resolution of the CMS electromagnetic calorimeter. A new diode-pumped solid state blue laser was commissioned and installed at CERN for 2012 operation. This laser has a simple structure and is more reliable than the existing lamp-pumped lasers used by the monitoring system. The stability of critical parameters, such as the pulse energy, width and centre timing, is much better than that of the lamp-pumped lasers. The characteristics of this blue laser are described. Its performance in-situ at LHC is elaborated. The prospects for improving the light monitoring precision are discussed.