1. 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

2. 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: Hz, the maximum rate allowed by DAQ.
IEEE Trans. Nucl. Sci. vol. 52 pp , 2005

3. 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

4. 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

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

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

7. 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

8. 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

9. 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.

10. Performance without Software Feedback
Performance published in IEEE Trans. Nucl. Sci. vol. 52 pp , 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.

11. 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

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

13. 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.