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

Outline

AsideMotivationSetupPower amplification testsFurther TestsChallengesConclusions

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

LSU Quad Pass Optical SetupDec 2006

Setup Photos

Single Pass

LIGO

LightwaveMOPA

Relay Optics Amplifier

Detectors

Amplifier

Setup

Single Pass: The Detectors

Power Meter

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

It is not the table shaking

Little coherence at 1 kHz

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)

Amp Housing

Vibrating Crystal

Laser Beam

Shaking Thermal Lens

Possible Mechanism for Jitter

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

THE END

Tracking Crystal Faces

Coherence data from Crystal Faces

Phase data from Crystal Faces

0 200 400 600 800 1000 1200400

200

0

200

Horizontal DataVertical Data

Transfer Function, Phase Data, Xtal Face

Frequency (Hz)

degr

ees