LSU Amplifier Experiments
Rupal S. Amin (LSU)
J. Giaime (LSU), D. Hosken (Uni. Adelaide), D. Ottaway (MIT)
LSC/VIRGO Meeting March 2007Lasers Working Group
DCC-G070147-00-R
Aside:Reminder of Optical Amplifier
Scheme of an ideal (inverting) electrical amplifier
Vout: Amplified signal with identical variations as V in
Vin
R1
R2
Vout = - R2/R1* Vin
Aside:
Scheme of optical amplifier
Pin = 100W Pout = 200 W
Pout : Amplified laser power with identical variations as P in
Lasing Crystal,Pump Housing,Cooling
Motivation
Competing ideas* in 2004 for Fall 2007 upgradeoAmplifier downstream of MOPA (LSU)oNew laser head (LZH)oNew injection locked slave laseroReplace current MOPA’s NPRO with more powerful NPRO
Investigate and offer a quick upgrade to LIGOOffer simple installation using off-the-shelf technology
*: D. Ottaway, LIGO-T040063-00-D
LSU’s AmplifierModel: RBA25
Manufacturer: Cutting Edge Optronics/Northrop Grumman Corp.
Diode Bar (5/15)
Crystal rod: 2 mm dia by 80 mm lengthWater cooled (68 psi/1GPM water flow )
Mechanical Cross Section
Diode Bars
Crystal Cooling Jacket
Diode Bar Cooling
Crystal Suspended in Cooling Jacket by O-rings
LSU Single Pass Optical Setup2006
Half-wave Plate
LIGO126 MOPA
QPD
PowerMeter
Mirror or WedgeBeam splitter
Periscope
Amplifier
Faraday
Lens
Beam Dump
Iris
LSU Double Pass Optical Setup2006
Half-wave Plate
LIGO126 MOPA
QPD
PowerMeter
Mirror or Wedge
Beam splitter
Periscope
Amplifier
Faraday
Lens
Beam Dump
Iris
Initial power amplification testsSingle Pass
0 1 2 3 4 5 6 7 80
5
10
15
20
Injected Power (W)Amplifier 0 AmpsAmplifier at 17 AAmplifier 22 AmpsSimulation 17 ASimulation 22 A
Injected Power (W)
Am
plif
ied
Pow
er (
W)
Tests performed at LASTI (MIT)
0 2 4 6 8 10 12 14 16
0
0.02
0.04
0.06
0.08
0.1Depolarization Level
Emitted Polarized Light Power (W)
Dep
olar
izat
ion
Rat
io
Depolarization
PDepol
Ratio = Ptotal
22 Amps
Angular JitterA Magnitude of Problems
1 10 100 1 103
1 104
1 1010
1 109
1 108
1 107
1 106
1 105
1 104
SML OnlyChiller OnAmplifier Pump Current 17 AAmplifier Pump Current 22 A
Frequency (Hz)
Am
plitu
de R
ad r
ms/
sqrt
(Hz)
Jitter peaks >10x above MOPABump at 1 kHzSingle Pass
*SML: “Spare Main Laser”
1 10 100 1 103
1 104
1 1011
1 1010
1 109
1 108
1 107
1 106
1 105
1 104
SML OnlyChiller OnAmplifier Pump Current 17 AAmplifier Pump Current 22 A
Frequency (Hz)
Am
plitu
de R
ad_r
ms/
sqrt
(Hz)
Angular Jitter (No Faraday) Fall 2006
Angular Jitter
Leads toPointing ProblemsAmplitude variations in downstream cavities
If the problem is caused by Xtal Vibration
•Phase noise due to crystal bending•Problems in polarization quality
If the problem is something else on the table, then identify it.
So what is causing angular jitter?
What’s the target?Jitter of LIGO MOPA’s
Probable Causes
Pressure waves in the cooling pipes?
10 100 1 103
1 104
1 105
1 104
1 103
0.01
0.1
1
Pressure BackgroundSML and Chiller OnAmp on, Pump Current = 8.0 AAmp on, Pump Current = 17.0 AAmp on, Pump Current = 22.0 ASept 5, 2006 Low Flow Data
Pressure Noise with New Plumbing
Frequency (Hz)
PS
IG r
ms/
sqrt
(Hz)
½” , 22 ft. hose
1”,50 ft. hose
Coherence Data Between Pressure Fluctuations and Jitter
No Significant Coherence Between Pressure Fluctuations and Pointing Jitter.
Both pipes, no difference
0 500 1000 1500 2000 2500 3000 35001 10
6
1 105
1 104
1 103
0.01
Jitter of SML onlyPump pressure 12 psi, no flow registered15 psi, no flow20 psi, ~0.25 gpm25 psi, <0.4 gpm30 psi, 0.6 gpm35 psi, 0.6 gpm40 psi, 0.75 gpm45 psi, 0.82 gpm
Jitter as a function of head pressure
Frequency (Hz)
Culprit:Water Flowing Inside Amp
Jitter Drops with Lower Flow
0 500 1000 1500 2000 2500 3000 35001 10
10
1 109
1 108
1 107
1 106
1 105
Jitter SML onlyAmplifier at 8 A pump currentAmplifier at 17 A pump currentAmplifier at 22 A pump current
Horizontal Jitter Cold Test
Frequency (Hz)
Rad
rm
s/sq
rt(H
z)
Jitter Spectra at Reduced Flow
Chiller Pressure 16 PSIGWater Temp Reduced from 23 deg C to 16 deg C60 Hz Power Lines VisibleBetter above 500 Hz
10 100 1 103
1 104
1 1010
1 109
1 108
1 107
1 106
1 105
Jitter SML onlyAmplifier at 8 A pump currentAmplifier at 17 A pump currentAmplifier at 22 A pump current
Horizontal Jitter Cold Test
Frequency (Hz)
Rad
rm
s/sq
rt(H
z)
Intensity Noise
Intensity Noise increases with amplifier by 2x Dominated by 60 Hz components Double Pass data
10 100 1 103
1 104
1 109
1 108
1 107
1 106
SML onlySML with the Chiller OnChiller On, Pump Current = 8 AChiller On, Pump Current = 17 AChiller On, Pump Current = 22 A
Intersity Noise Upper Estimation
Frequency (Hz)
W/s
qrt(
Hz)
Hurdles
Requested power for Fall 2007 upgrade, 30 WoMaximum power estimated from amplifier quad pass, 22 W
Instrumentation:oTemperature control of x-tal and laser diodesoCurrent/laser power control
Amplitude/Frequency/Phase Noise?
Conclusions
oGood power outputoRequire a larger crystal for 30 WoThicker crystal would reduce beam jitteroCould be used as patch for a failing MOPA