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Sensing and control, SPIE conference, June 2004 1LIGO- G040310-00-R
Sensing and control ofthe Advanced LIGO optical
configuration
SPIE conference at GlasgowJune 23, 2004
O. Miyakawa, Caltech
B. Abbott, R. Bork, P. Fritschel, L. Goggin, J. Heefner, A. Ivanov,S. Kawamura, F. Kawazoe, C. Mow-Lowry, A. Ourjoumtsev, S. Sakata,
M. Smith, K. Strain, R. Taylor, D. Ugolini, S. Vass, R. Ward, A. Weinstein
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Sensing and control, SPIE conference, June 2004 2LIGO- G040310-00-R
Signal and power enhancement using Fabry-Perot cavity in each arm
Power enhancement using Power Recycling
Optical configuration forGravitational wave interferometer
Gravitational wave detection using Michelson interferometer
BS
FP cavity
FP
ca
vit
y
Laser
PRM
BS
FP cavity
FP
ca
vit
y
Laser
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Sensing and control, SPIE conference, June 2004 3LIGO- G040310-00-R
LIGO:Power recycled FPMI
» Optical noise is limited by Standard Quantum Limit (SQL)
AdvLIGO:GW signal enhancement using Detuned Resonant Sideband Extraction
» Can overcome the SQL QND detector
» Two dips by optical spring, detuning
Advanced LIGO optical configuratoin
Detuning
PRM
BS
FP cavity
FP
ca
vit
y
Laser
GW signal
Power
Standard Quantum Limit
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Sensing and control, SPIE conference, June 2004 4LIGO- G040310-00-R
Caltech 40 meter prototype interferometer
Objectives Develop lock acquisition procedure of suspended-mass
detuned Resonant Sideband Extraction (RSE) Characterize noise mechanism Verify optical spring effect Develop readout scheme
for Advanced LIGO and other future GW detectors
BSPRM SRM
X arm
Y arm
Darkport
Brightport
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Sensing and control, SPIE conference, June 2004 5LIGO- G040310-00-R
Length sensing and control
Phase lock
Feedback~
Locked
Sidebands (probe for carrier)
Carrier
L
Sig
nal[
a.u.
]
Unlocked
PD
EOM:Modulation
Mixer :Demodulation~
Oscillator~MHz
L
Error signal
Lock point
Locking area
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Sensing and control, SPIE conference, June 2004 6LIGO- G040310-00-R
Signal extraction for AdvLIGO
Arm cavity signals are extracted from beat between carrier and f1 or f2.
Central part (Michelson, PR, SR) signals are extracted from beat between f1 and f2, not including arm cavity information.
f1-f1 f2-f2
Carrier (Resonant on arms)• Single demodulation• Arm information
• Double demodulation• Central part information
ETMy
ETMx
ITMy
ITMxBSPRM
SRM
Two modulations are used to separate high finesse, 4km long arm cavity signals from Central part (Michelson, PR, SR) signals.
4km
4k
m
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Sensing and control, SPIE conference, June 2004 7LIGO- G040310-00-R
5 DOF for length control
Laser
ETMy
ETMx
ITMy
ITMxBS
PRM
SRM
SPAP
PO
lx
ly
lsx
lsy
Lx
Ly
: L=( Lx Ly) / 2
: L= Lx Ly
: l=( lx ly) / 2
: l= lx ly
: ls=( lsx lsy) / 2
Port Dem. Freq.
L L l l l s
SP f1 1 -3.8E-9 -1.2E-3 -1.3E-6 -2.3E-6
AP f2 -4.8E-9 1 1.2E-8 1.3E-3 -1.7E-8
SP f1 f2 -1.7E-3 -3.0E-4 1 -3.2E-2 -1.0E-1
AP f1 f2 -6.2E-4 1.5E-3 7.5E-1 1 7.1E-2
PO f1 f2 3.6E-3 2.7E-3 4.6E-1 -2.3E-2 1
Signal Extraction Matrix (in-lock)
Common of armsDifferential of armsPower recycling cavityMichelsonSignal recycling cavity
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Sensing and control, SPIE conference, June 2004 8LIGO- G040310-00-R
Disturbance by sidebands of sidebands
Sidebands of sidebands are produced by two series EOMs. Beats between carrier and f2 +/-f1 disturb central part.
Original concept Real world
f1-f1 f2-f2
Carrier
f1-f1 f2-f2
Carrier
Port Dem. Freq.
L L l l l s
SP f1 1 -1.4E-8 -1.2E-3 -1.3E-6 -6.2E-6
AP f2 1.2E-7 1 1.4E-5 1.3E-3 6.5E-6
SP f1 f2 7.4 -3.4E-4 1 -3.3E-2 -1.1E-1
AP f1 f2 -5.7E-4 32 7.1E-1 1 7.1E-2
PO f1 f2 3.3 1.7 1.9E-1 -3.5E-2 1
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Sensing and control, SPIE conference, June 2004 9LIGO- G040310-00-R
Mach-Zehnder on 40m PSLto eliminate sidebands of sidebands
Series EOMswith sidebands of sidebands
EOM2EOM1
Mach-Zehnder interferometerno sidebands of sidebands from beginning
PD
EOM1
EOM2
PZT mirrorBS1
BS2
33MHzEOM
166MHzEOM
29MHzEOM
PD
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Sensing and control, SPIE conference, June 2004 10LIGO- G040310-00-R
Lock Acquisition of Detuned RSE
2. lock arm cavities1. lock central part using beat signal between f1 and f2
ETMy
ETMx
ITMy
ITMxBSPRM
SRM
ITMy
ITMxBSPRM
SRM
Step 2Step 1Step 3
Central part: not disturbed by lock status change of arm cavity
Find primary signal not disturbed by the other two DOFs
Find secondary signal not disturbed by the residual DOF
Arm cavities: not disturbed by locked central part
Lock each arm cavity independently
Switch control servo to common/differential control
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Sensing and control, SPIE conference, June 2004 11LIGO- G040310-00-R
l- signal with double demodulation
Good l- signal when l+ and ls is locked
No good l- signal once l+ and ls start moving
Lock point
Lock point
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Sensing and control, SPIE conference, June 2004 12LIGO- G040310-00-R
l- signal with double demodulation
Good l- signal when l+ and ls is locked
No good l- signal once l+ and ls start moving
Lock point
Lock point
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Sensing and control, SPIE conference, June 2004 13LIGO- G040310-00-R
Looking for good signal for lock acquisition
Unfortunately, no way to lock central part directly using the original double demodulation
Dither locking for l- signal
Divide signal by inside power» Good cancellation of power recycling
2PO
POAPPOAP
PO
AP
-
V
VVVV
V
V
ld
dVl
Laser
ITMy
ITMxBS
PRM
SRM
SPAP
PO
~
1
Vl
LPF LPF LPF LPF
Digital calculation
(VPO)’ (VAP)’VPO VAP
a few kHz
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Sensing and control, SPIE conference, June 2004 14LIGO- G040310-00-R
l- signal with dither
Dither on ITMx, ITMy with 1kHz
Error signal is calculated digitally as follows;
l- signal does not depend on l+ at all
Good l- signal obtained with all ls movement
Lock point
Lock point
2PO
POAPPOAP
PO
AP -
V
VVVV
V
V
ld
dVl
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Sensing and control, SPIE conference, June 2004 15LIGO- G040310-00-R
l+ signal with l- lock
Zero crossing point of l+ corresponds with movement of ls
Distance between PRM and SRM is kept
Good l+ signal obtained with all ls movement
Lock point
Lock point
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Sensing and control, SPIE conference, June 2004 16LIGO- G040310-00-R
ls signal with l- and l+ lock
Good ls signal can be extracted
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Sensing and control, SPIE conference, June 2004 17LIGO- G040310-00-R
Summary
Optical configuration for AdvLIGO being developed at 40m prototype interferometer
Sidebands of sidebands: eliminated by M-Z interferometer
Ready to try lock acquisition Lock acquisition: promising with dither lock
Hope we succeed in locking detuned RSE very soon!