On behalf of the Caltech Laser Group Upgrade of the Laser Monitoring System A major upgrade of the laser system was carried out in May, 2006: - New hardware - New software - Result David BAILLEUX On behalf of the Caltech Laser Group Test Beam meeting - 19 th July 2006 -

Laser Source Requirements Pulse width: FWHM < 40ns to match PWO readout. Pulse jitter: <4ns/<2ns for long/short term. Pulse energy: 0.4 mJ/pulse to provide more than 100 GeV equivalent energy deposition in each crystal. Pulse energy instability: <10%. Pulse rate: 100Hz, the maximum rate allowed by DAQ. IEEE Trans. Nucl. Sci. vol. 52 pp. 1123-1130, 2005

Laser Setup until May, 2006 Ext.trigger (<100 Hz) Pulse timing Laser3 system: spare, 440nm Ext.trigger (<100 Hz) Pulse timing 80 fibers (2/SM) 150m long Ethernet Communication

Laser Setup after June, 2006 Ext.trigger (<100 Hz) Pulse timing Laser3 system: spare, 440nm Ext.trigger (<100 Hz) Pulse timing 80 fibers (2/SM) 150m long Ethernet Communication Shot 102 2 stage Driver 5x1 optical switch New box

Old & New Racks 1x2 optical switch 1x5 optical switch

New Attenuation Box both linear and logarithmic attenuators are remote controlled 2 Remote control neutral filters 0-10-20-30-40-50db linear 1 to 99% Input from 1x2 switch Output PIN Diode  Pulse monitoring &Matacq PIN Diode pulse timing to XDAQ

New Laser DAQ Software feedback: tested in several individual runs, 3 lasers online with 1 x 5 switch, hardware & data acquisition in separated processes. End 2005 From June, 2006

Principle of the Software Feedback Compensates the long term Ti:S pulse drift, caused by the YLF lamp aging *. Looking for variation of the TiS pulses: Energy, FWHM or Center 2) Trim the YLF current according to the measured average values for the selected parameter according to the corresponding slope. * YLF lamp life time: ~1000 to 2000hrs Effect with time

Implementation of the Software Feedback For each laser: - On/Off: enabled/disabled feedback parameter: YLF or TiS parameters (Energy – FWHM – Center) counter: number of events required to calculate average values for the selected parameter slope: value defined by calibration (see previous slide) current limit: min and max for protection Current incremental step: 0.1 A (hardware limit) Tests of feedback  Ti:S pulse center timing feedback selected.

Performance without Software Feedback Performance published in IEEE Trans. Nucl. Sci. vol. 52 pp. 1123-1130, 2004: Long term (25 h) stability of the pulse energy and width at 3% level for blue and IR. Before upgraded 6 days for the Laser2 in April, 2006.

Performance with the Software Feedback 10 days for the laser 2 in May 2006 : feedback parameter  Ti:S pulse center timing Result: YLF pumping current was automatically increased by 0.5 A A factor of two better stability has been achieved in this test run

Last slow monitoring runs 7 days for the Laser 2 starting June 12

Summary New hardware: an 1 x 5 switch, a new attenuation box with logarithmic and linear attenuators.  New software, function added to the laser DAQ program: 3 lasers on-line with 1 x 5 switch, remote control of both logarithmic and linear attenuators, run control and the slow monitor in separated processes.  Result: The software feedback works exactly as expected in a test run lasting for 10 days when the YLF pumping current was increased automatically by 0.5 A in 5 steps to compensate the Ti:S pulse center timing degradation. Significant improvement in the laser stability (energy, FWHM and jitter) was observed.  Work to be done in software development: Test the remote control of the logarithmic attenuator with laser supervisor (XDAQ); Implement the software feedback beyond one laser DAQ run; Implement selective firing of the laser system to minimize unnecessary laser mileage.