Laser Long Term Performance & Pulse Width Issueslaser-caltech.web.cern.ch/laser-caltech/report/Laser... · 2005-09-19 · The Laser Workshop Adi Bornheim California Institute of Technology

The Laser Workshop

AdiAdi BornheimBornheimCalifornia Institute of TechnologyCalifornia Institute of Technology

CERN, September 16, 2005CERN, September 16, 2005

Laser Long Term Performance& Pulse Width Issues

September 16, 2005 A.Bornheim - Laser Workshop - CERN 2

Outline

Part 1 : Laser long term performance 2003 - 2005

Interlude : Convoluting Pulses

Part 2 : APD/PN pulse width dependence.


Laser Long Term Performance

What is long term ?‘Natural scales’ :

LHC cycle : 24 h 1 dayAccelerator ‘maintenance cycle’ : 1 week (SPS), @ LHC ? 7 days

YLF Lamp aging : 500 h to 1000 h 20 – 40 days‘Various’ other laser parts (eg. flowtube) : 1 year 365 days

Accumulation of luminosity for In-situ calibration : few months ~60 days more are startup >>60 days

Over which time scale do we have to achieve the stability requirements ?


Laser Operation 2003 – Beam Periods

Time [hours]

Int_

rel

‘normal’ & stable running heavy ion with SM0 h.i. with SM1

air conditioning problem

laser internal monitoring problem

440nm500 nm

800 nm700 nm

2003 was the only time we ran the laser on green (and red). The benefit is unclear.


Time [hours]

Int_

rel

Laser Operation 2003 - Setup Period

20.08. 28.08. power tuning for ECAL


Int_

rel

Time [hours]blue monitor broken

air conditioning problem

Beam on ECAL Beam on ECAL



Time [hours]

Int_

rel SM cooling problem SM LV problem

laser internal trigger

blue laser cooling ?



YLF lamp aging - 2003In

t_re

l

Time [hours]Time [hours]In

t_re

l

440 nm 800 nm

Pump lamp for pump laser degrades over time→ Pulse energy degradation for constant pump current.

For blue laser (runs at higher pump current, here 25 A) :Mean degradation : 0.41%/day - 12.4%/month

For red laser (runs at 20 A):Mean degradation : 0.057%/day - 1.72%/month

This can be compensated by increasing the pump current and replacing the pump lamp.The pump current adjustment can be automated with a feedback system.

It was decided to not touch the lasers during the period shown above to ensure stable running.


Hardware Trouble – Spring 2004

0.36

0.38

0.4

0.42

0.44

0.46

0.48

0.5

600 650 700 750 800 850

. Time [hours]

Int_

rel

-1.28 %/day

-1.97 %/day

-1.67 %/day

Was later traced to damaged optical components. Laser 2 had a hardware problem at the same time - which was later traced to a broken flowtube.

At the time it was decided not to intervene but to continue data taking !

Laser 1

440nm


Comparison Degradation 2003 / 2004

Note : Intensity Scale Arbitrary !!!Aligned to have common ‘0’.(However : Scale agrees with power settings)

2004 : ~ -1.6%/day (w.r.t. 0.5)2003 : ~ -0.4%/day (w.r.t. 0.28)0.36

0.38

0.4

0.42

0.44

0.46

0.48

0.5

600 650 700 750 800 850

.

Time [hours]

Puls

e En

ergy

2004

2003

440nm


Pulse width history - Spring 2004

Time [hours]

Puls

e W

idth

[ns]

Hardware problems can cause non-standard behavior !Pulse width seems to be not affected as much as pulse energy. Anti-correlation not as strong as normally.

Time [hours]

0.36

0.38

0.4

0.42

0.44

0.46

0.48

0.5

600 650 700 750 800 850

.

Puls

e En

ergy 440nm


Laser Operation SM10 – Fall 2004

750 hours

!!

?

Fast Monitor Data

Cooling Problem

Electronics/Cooling ProblemWidth

Height

Overall performance good. Three ‘hick ups’ during 750 hours operation – one of unknown source.Two ‘non standard’ – height and width change in the same direction – incidents.

Pulse Width

Fast monitor (event by event) averaged over one run.

Fast Monitor Data

440nm


Laser operation (440 nm) 2005

23

24

25

26

27

28

29

30

31

32

1000 1200 1400 1600 1800 2000Time [ h ]

Mea

n T

iS W

idth

[ n

s ]

5.8.

2005

1.8.

2005

15.8

.200

5

20.8

.200

5

25.8

.200

5

30.8

.200

5

1.9.

2005

5.9.

2005

10.9

.200

5

15.9

.200

5

1

1.2

1.4

1.6

1.8

2

2.2

2.4

1000 1200 1400 1600 1800 2000Time [ h ]

Mea

n T

iS E

ner

gy

20.8

.200

5

25.8

.200

5

30.8

.200

5

1.9.

2005

5.9.

2005

10.9

.200

5

15.9

.200

5

15.8

.200

5

5.8.

2005

1.8.

2005

Laser 1Laser 2

IPump=23 AIPump=22 A

To be adjusted in LaserSupervisor

Operation so far good.Continue to optimize retuning procedure to match pulse width and height.

~0.5%/day


Pulse Timing Drift - 2005

Pulse Time is anti-correlated to the pulse energy and correlated to the pulse width !The return signal from the laser DAQ guarantees proper timing of the ECAL readout.The timing of the TiS pulse drifts over several LHC clock cycles on the time scale ofweeks.

50

100

150

200

250

300

350

1000 1200 1400 1600 1800 2000

Elapsed Time [ h ]

TIS

Pul

se T

ime

[ ns

]

5.8.

2005

1.8.

2005

10.8

.200

5

15.8

.200

5

20.8

.200

5

25.8

.200

5

30.8

.200

51.

9.20

05

5.9.

2005

10.9

.200

5

15.9

.200

5

Compare previous Page :There can be shifts in pulse timing independent of pulse energy/width

Pulse width scan


Laser Source Performance

1.8%1.4%1.1%

1.3% 1.3%

3.5%3.7%

1.7%

Stability over periods of 5 days :

The lasers were tuned to optimize the pulse width stability – seems to work.2003 : 440 nm 800 nm

Pulse Height : 2.6% / 25 hours 3.2% / 25 hours1.5%/ 30 min 2.8% / 30 min0.4%/day (long term) 0.06%/day (long term)

Pulse Width : 2.7% / 25 hours 2.6% /25 hours


Short Term Stability - 2003

440 nm

800 nm

495 nm

700 nm8.2 %3.2 %

7.6 %2.6 %tref : 330 - 335 h

440 nm

800 nm

495 nm

700 nm

pulse width [ns]

5.7 %2.6 %

6.8 %2.7 %

tref : 330 - 335 h

25.7 ns

23.9 ns 36.3 ns

65.8 ns

440 nm 800 nm

pulse time [ns]

2.8 ns 1.5 ns

pulse height

Note : The higher the pump current the better the short term stability. In 2003 we used a higher pump current than in 2004 & 2005.


Convoluting Pulse ShapesThe sampled pulse is a convolution of the electronic shape and the laser pulse shape. We then estimate the energy from the pulse height.

0

0.2

0.4

0.6

0.8

1

0 25 50 75 100 125 150 175 200 225 250

Time [ ns ]

Rel

ativ

e P

uls

e H

eig

ht

20 ns25 ns

30 ns35 ns40 ns

Shape Function ))(exp())(

()( maxmax

peakpeak

peak

TTt

TTTt

tf −×−

−−= αα

Laser shape (Gauss with FWHM 20 ns, .. , 40 ns)convoluted with shape function.

Parameters for shape function adjusted to matchvalues measured as from Renauld’s talk 16.03.2005.

0

0.05

0.1

0.15

0.2

0.25

0.3

300 400 500 600 700 800 900 1000

Time [ ns ]

Pu

lse

hei

gh

t

APD

PN

0.28321

0.28322

0.28323

0.28324

0.28325

0.28326

0.28327

0.28328

780 785 790 795 800 805 810 815 820

Time [ ns ]

Pu

lse

hei

gh

tEffect strongly depends on the rise time !Sizable for APD - Negligible for PN.

50 ns


Pulse Shape Convolution (con’t)

0.8

0.85

0.9

0.95

1

1.05

1.1

1.15

1.2

20 22.5 25 27.5 30 32.5 35 37.5 40

Pulsewdith [ ns ]

AP

D/P

N

APD/PN Ratio from previous page

Effect (slope) is of the order of 0.006/ns.But this number is strongly (within a factor 2) rise time dependent.


Pulse Width Dependence in Data

∆R = 0.085

∆T = 4 ns

Normalize R to 1 ⇒ Slope : ~ 0.003/ns

Plot from R. Salerno

Marc, WACH2002, Paris, 2002 Data

Pulse width ~40 ns ??

Slope : ~ 0.002/ns But : Pulse width determination different.

Note : Here very different setups are compared (electronics, width measurement, etc.).


Pulse Width Scan – Spring 2004Compare : Adi’s talk on 06.10.2004

IPump : 25 A

IPump : 19 A

Nominal IPump for last SC beam period: 22 A

TiS Pulse Energy vs Pulse Width

Attempt to compensate pulse energy change with the intensity regulator ‘online’ to isolate pulse width effect. Since pulse height non-linearity is much smaller this is not necessary.

APD/PN pulse width dependence

0.006/ns

From MATACQ

From fast monitor

From fast monitor


Laser Pulse Width Correction - 2004Please recall Patrice’s presentation at test beam meeting on 18.05.2005 :

Period 1 Period 2 Period 3

Period 1 : Stable runningPeriod 2 : H4 DAQ trouble (timing ?) Period 3 : Running After period 3 : Temperature step, HV scan, laser scans, token ring broken …

Note : The laser problems in this period have nothing to do with the H4 DAQ trouble.


Pulse Width Correction on SM10 - 2004

Uncorrected

Corrected

ECAL APD/PN, Single Channel Monitoring History

Laser Pulse Height

Laser Pulse Width

450 Hours

Fast Monitor Data

Data analysed : Part of Period 1 (not all the data was re-reprocessed to fix PN data) and Period 3. Period 2 is problematic - and thus not used.

Pulse width correction :APD/PN_cor = APD/PN+c·PW_Laser


Pulse Width Correction Performance

Uncorrected

Corrected

Monitoring stability over 450 hours : ~0.1 %

Judge performance (monitoring stability) by projecting values onto Y-Axis for each channel (actually 400 for the plot shown) and determine the RMS.

Period 1 and Period 3 combined.


Summary & Outlook

The long term laser performance and our understanding of its limitations improved over the three years the system is in operation.Pulse energy and pulse width can be kept stable within the requirements for several weeks. We continue to improve the operation of the laser to minimize the impact of maintenance operation and hardware failures.The pulse width dependence of the APD/PN ratio remains a critical issue. It appears that a width stability on the level of <1ns is needed.

Analyse SM5 pulse width scan data as soon as rrf-files are available.Perform further scans on SM5 and on further SM as they become available. Presumably the effect is not channel-to-channel depedent.

Documents

Laser Long Term Performance & Pulse Width Issueslaser-caltech.web.cern.ch/laser-caltech/report/Laser... · 2005-09-19 · The Laser Workshop Adi Bornheim California Institute of Technology