optical springs at the 40m 1 qnd workshop, hannover dec 14, 2005 robert ward for the 40m team osamu...
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Optical Springs at the 40m 1
Optical Springs at the 40m
QND Workshop, HannoverDec 14, 2005
Robert Wardfor the 40m Team
Osamu Miyakawa, Rana Adhikari, Matthew Evans, Benjamin Abbott, Rolf Bork, Daniel Busby, Hartmut Grote, Jay Heefner,
Alexander Ivanov, Seiji Kawamura, Michael Smith, Robert Taylor, Monica Varvella, Stephen Vass, and Alan Weinstein
Optical Springs at the 40m 2
An interferometer as close as possible to
the Advanced LIGO optical configuration and control system
Caltech 40 meter prototype interferometer
Detuned Resonant Sideband Extraction (DRSE)
Power Recycling Suspended mass
Single pendula Digital controls system Same cavity finesse as
AdLIGO baseline design 100x shorter storage times.
Optical Springs at the 40m 3
AdLIGO signal extraction scheme
Arm cavity signals are extracted from beat between carrier and f1 or f2.
Central part (Michelson, PRC, SRC) 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
Mach-Zehnder will be installed to eliminate sidebands of sidebands.
Only + f2 is resonant on SRC. Unbalanced sidebands of +/-f2 due
to detuned SRC produce good error signal for Central part.
ETMy
ETMx
ITMy
ITMxBSPRM
SRM
4km
4k
mf2
f1
Optical Springs at the 40m 4
The Story So Far
To understand why we saw the optical springs in the way we have, it helps to know the story of Lock Acquisition at the 40m.
Optical Springs at the 40m 5
Transmitted light is used as
40m Lock Acquisition part I: Off-resonant lock scheme for a single cavity
Off-resonantLock point
Resonant Lock
offsetpower dTransmitte
1
Optical Springs at the 40m 6
40m Lock acquisition procedure
Start withno DOFscontrolled, all optics aligned.
ITMy
ITMxBS
PRM
SRM
SP DDM
13m MC
33MHz
166MHz
SP33SP166
AP DDM
AP166
PO DDM
Optical Springs at the 40m 7
40m Lock acquisition procedure
DRMI + 2armswith offset
ITMy
ITMxBS
PRM
SRM
SP DDM
13m MC
33MHz
166MHz
SP33 SP166
AP DDM
AP166
PO DDM
Average wait : 3 minute (at night, with tickler)
T =7%
T =7%IQ
1/sqrt(TrY)
1/sqrt(TrX)
Optical Springs at the 40m 8
40m Lock acquisition procedure
ITMy
ITMxBS
PRM
SRM
SP DDM
13m MC
33MHz
166MHz
SP33 SP166
AP DDM
AP166To DARM
PO DDM
AP166 / (TrX+TrY)
CARM
DARM+
-1+
Short DOFs -> DDMDARM -> RF signalCARM -> DC signal
1/sqrt(TrX)+ 1/sqrt( TrY)
CARM -> Digital CM_MCL servo
Alternative path
Optical Springs at the 40m 9
40m Lock acquisition procedure
Reduce CARM offset:1. Go to higher ARM power
2. Switch on AC-coupled analog CM_AO servo, using REFL DC as error signal.
3. Switch to RF error signal (POX) at half-max power.
4. Reduce offset/increase gain of CM_AO.
ITMy
ITMxBS
PRM
SRM
SP DDM
13m MC
33MHz
166MHz
SP33
SP166
AP DDM
AP166To DARMREFL
DARM-1
PO DDM
AP166 / (TrX+TrY)
GPR=5
5. Packup MOPA and send it to LLO for S5
Optical Springs at the 40m 10
Optical spring in detuned RSE
a :input vacuumb :outputD :M :h :strain
A. Buonanno, Y.Chen, Phys. Rev. D 64, 042006 (2001)
SQL2
1)(
2
1
2221
1211)(2
2
1 21
h
h
D
De
a
a
CC
CCe
Mb
b ii
cossin
cossin cossin2
21
2221212111
SQL
DD
aCCaCCb
bh
hn
hSQL:standard quantum limit: transmissivity of SRM: coupling constant: GW sideband phase shift in SRC: GW sideband phase shift in IFO
: homodyne phase
Optical spring in detuned RSE was first predicted using two-photon formalism.
a b
Dlaser
Signal recyclingmirror
h
h
Optical Springs at the 40m 11
Detune Cartoon
0C
arri
er f
requ
ency
-10000 -5000 0 5000 10000
50
100
200
500
1000
frequency offset from carrier [Hz]
Sid
eban
d am
plit
ude
[a.u
.]
FWHM
USBLSB
fsig
•Responses of GW USB and GW LSB are different due to the detuning of the signal recycling cavity.
•IFO Differential Arm mode is detuned from resonance at operating point
00
SRC DARM
IFO DARM/CARM
slope related to spring constant?
•IFO Common Arm mode is detuned from resonance at intial locking point
00
PRC CARM
Optical Springs at the 40m 12
DARM TFs as CARM offset is reduced
Optical Springs at the 40m 13
CARM optical springs
102
103
80
90
100
110
120
130
140CARM optical springs at different CARM offsets
f (Hz)
CA
RM
opt
ical
res
pons
e (d
B)
Arm power = 6
Arm power = 8Arm power = 10•Solid lines are from TCST
•Stars are 40m data•Max Arm Power is ~80•Also saw CARM anti-springs, but don’t have that data
Optical Springs at the 40m 14
Optical spring and Optical resonance in differential arm mode of detuned RSE
• Optical gain of L- loopDARM_IN1/DARM_OUT divided by
pendulum transfer function
• Optical spring and optical resonance of detuned RSE were measured.
• Frequency of optical spring depends on cavity power, mass, detuning phase of SRC.
• Frequency of optical resonance depends on detuning phase of SRC.
• Theoretical line was calculated using A. Buonanno and Y.Chen’s equations.-150
-100
-50
0
50
100
150
Pha
se[d
eg]
102 3 4 5 6 7 8 9
1002 3 4 5 6 7 8 9
10002 3 4 5 6 7
Frequency[Hz]
60
40
20
0
-20
Mag
[dB
]
Measured data Theoretical line
Measured optical gain of arm differential mode in detuned RSEOct 22, 2005
Optical Springs at the 40m 15
Positive spring constant
-150
-100
-50
0
50
100
150
Pha
se[d
eg]
102 3 4 5 6 7 8 9
1002 3 4 5 6 7 8 9
10002 3 4 5 6 7
Frequency[Hz]
-40
-20
0
20
40
Mag
[dB
]
Measured data Theoretical line
Measured optical gain of arm differential mode in detuned RSEOct 13, 2005
• SRM is locked at opposite position from anti-resonant carrier point(BRSE).
• Optical spring disappeared due to positive spring constant.
BroadbandRSE
BroadbandSR
Optical Springs at the 40m 16
Simple picture of optical spring in detuned RSE
Let’s move arm differentially, X arm longer, Y arm shorter from full RSE
PowerX arm down, Y arm up X arm down, Y arm down X arm up, Y arm down
Radiation pressureX arm down, Y arm up X arm down, Y arm down X arm up, Y arm down
Spring constantNegative(optical spring) N/A Positive(no optical spring)
DARM (Lx-Ly) DARM (Lx-Ly)
DARM (Lx-Ly)
Pow
er(W
)
Pow
er(W
)
Pow
er(W
)
BRSECorrect SRM position Wrong SRM position
X arm X armY arm Y arm
Optical Springs at the 40m 17
Relationship between the CARM and DARM springs at the 40m
With the 40m Lock Acquisition scheme, we only see a CARM spring if there’s also a DARM spring.
Details tomorrow
Xarm Yarm DARM CARM
+ + x x
- - 0 +
+ - x x
- + + -
•Using the DC-locking scheme for the arms, there are, prima facie, four locking points corresponding to the four possible gain combinations, but only two will acquire lock.
Xarm Yarm DARM CARM
+ + 0 -
- - x x
+ - - +
- + x x
Correct SRM position Incorrect SRM position
Optical Springs at the 40m 18
Will it lock?
-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
ETMX phi=90.0733
ETMY phi
Err
or
Sig
nals
Good SRM position
ERRDC
X
ERRDC
Y
NO
-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
ETMX phi=89.9267
ETMY phi
Err
or
Sig
nals
Good SRM position
ERRDC
X
ERRDC
Y
YES
•x-axis: EY position•y-axis: signal•blue:X err•green: Y err•black: DARM•red: CARM
modeled with FINESSE
Optical Springs at the 40m 19
Carrier33MHz166MHz
ITMy
ITMxBS
PRM
SRM
OSADDM PD
DDM PD
DDM PD
DRMI lock using double demodulation with unbalanced RF sideband in SRC
Carrier
33MHz
Unbalanced166MHz
Belongs tonext carrier
Belongs tonext carrier
Belongs tonext carrier
OSA
Optical Springs at the 40m 20
Unbalanced Sideband Detection
Kentaro Somiya “Photodetection method using unbalanced sidebands for squeezed quantum noise in a gravitational wave interferometer” PHYSICAL REVIEW D 67,122001 2003
A. Buonanno, Y. Chen, N. Mavalvala, “Quantum noise in laser-interferometer gravitational-wave detectors with a heterodyne readout scheme” PHYSICAL REVIEW D 67,122005 2003
Can not be used to circumvent the standard quantum limit, due to heterodyne noiseCan be used to change the measurement quadrature, and thus reshape the GW response
+166MHz sideband
demodulation phase
b1
b2
Optical Springs at the 40m 21
Changing the DARM quadrature
Story:1. Lock IFO with CARM offset2. Handoff DARM to RF 3. Adjust RF demodulation
phase4. Reduce CARM offset5. This changes the quadrature
of the signal. As we are not compensating for this by adjusting the demod phase, the shape of the response changes.
May also be some overall gain change due to imperfect normalization
Optical Springs at the 40m 22
Optickle Results
•GW response in a single, chosen quadrature at multiple CARM offsets
101
102
103
104
150
160
170
180
190
200
210
220
DARM opto-mechanical response in Q=1.07pi at different CARM offsets
f (Hz)
dB
Optical Springs at the 40m 23
Why is the correct SRM position harder to lock?
0
0.002
0.004
0.006
0.008
0.01
0.012
0.014
0.016
0 20 40 60 80 100 120 140 160 180
Abs
phi [deg] (SRM)
DRFPMI3 Tue Dec 13 00:07:37 2005
S21AP n2 :
S11AP n2 :
CAP n2 :
S12AP n2 :
S22AP n2 :
The correctly detuned SRC doesn’t lock as easily as the oppositely tuned SRCTrue for both full IFO and just the DRMI (though less noticeable on DRMI)For full IFO, lock time goes from 1 to 5 minutes.Have we just not tuned-it-up it right yet?
Optical Springs at the 40m 24
Mode healing/injuring at Dark Port
Negative spring constant with optical spring
Positive spring constant with no optical spring• Repeatable• The same alignment quality
Carrier power at DP is 10x smaller
Optical Springs at the 40m 25
Compensating the resonances
4kHz >> UGF
no compensation
AdLIGO: 180 Hz ~ UGF
40Hz < UGF
no compensation
AdLIGO: 70Hz?
1kHz -> 100Hz ~ UGF
dynamic compensation
0->100Hz ~ UGF
not coherently compensated
Compensation Filters for the various resonances:
Optical Opto-mechanical
DARM
CARM
UGFs ~ 250Hz
Optical Springs at the 40m 26
DARM loop: Calibration questions
D C S
P pendulum
DARM Cavityresponse
Sensing
A Actuator
F
Feedback filter
DARM_IN1
DARM_OUT
N G
N
1
DCSFAPG
G
DCSN
1
G
APGN
G
DCSFN
1
/
1
G
GN
1
DARM_IN2
EXC
Use DARM_IN1
•Measure DARM_IN2/EXC=
•Estimate S•Measure (or estimate) C
Use DARM_OUT
•Measure DARM_IN1/EXC=
•Estimate A•Estimate P
G1
1
G
G
1