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Demonstration of lock acquisition and
optical response on
Detuned RSE interferometer
at Caltech 40m
GWADW-VESF meeting @ Elba
May 31, 2006
Osamu Miyakawa, Caltech
+
40m team
LIGO- G060231-00-R
GWAWD-VESF meeting at Elba, May 2006
1
Advanced LIGO optical configuration
 LIGO:Power recycled FPMI
» Optical noise is limited by Standard
Quantum Limit (SQL)
FP cavity
 AdvLIGO:GW signal enhancement using
Detuned RSE
» Two dips by optical spring, optical
resonance
» Can overcome the SQL QND detector
Laser
PRM
Power
FP cavity
BS
GW signal
Detuning
SRM
LIGO- G060231-00-R
GWAWD-VESF meeting at Elba, May 2006
2
Historical review of Advanced
interferometer configuration
~1986
Signal Recycling
(Dual Recycling)
[B.Meers]
~1998
Garching 30m
[G.Heinzel]
GEO600
Glassgow 10m
~1993
RSE
•Idea [J.Mizuno]
•Tabletop [G.Heinzel]
~2000
Tabletop with new control
• Caltech(RSE)[J.Mason]
• Florida(DR)
• Australia(RSE)[D.Shaddock]
~2002
NAOJ 4m
Susp. mass
BRSE(No PR)
[O.Miyakawa]
~2005
Caltech 40m
• Suspended mass
• DRSE+PR
~2013
AdLIGO(DRSE)
LCGT(BRSE)
AdVIRGO
~2004
NAOJ 4m
Susp. mass
DRSE(No PR)
[K.Somiya]
~2001
QND study[Y.Chen, A. Buonanno]
•Optical spring
•Readout scheme
LIGO- G060231-00-R
GWAWD-VESF meeting at Elba, May 2006
3
Caltech 40 meter prototype interferometer
An interferometer as close as possible to
the Advanced LIGO optical configuration and control system
 Detuned Resonant
PRM
Sideband Extraction(DRSE)
 Power Recycling
 Suspended mass
Bright
 Digital controls system
port
 To verify optical spring
and optical resonance
 To develop DC readout
scheme
 To extrapolate to AdLIGO
via simulation
BS
SRM
Dark
port
X arm
Y arm
LIGO- G060231-00-R
GWAWD-VESF meeting at Elba, May 2006
4
Signal extraction scheme
ETMy
4km

f2


ITMy
PRM
BS
ITMx
ETMx
Mach-Zehnder is 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.
4km
f1
SRM
-f2
Carrier (Resonant on arms)
• Single demodulation
• Arm information
-f1
f1
f2
• Double demodulation
• Central part information


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.
LIGO- G060231-00-R
GWAWD-VESF meeting at Elba, May 2006
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Mach-Zehnder interferometer
to eliminate sidebands of sidebands
Series EOMs
with sidebands of sidebands
f1
Mach-Zehnder interferometer
with no sidebands of sidebands
PMC trans
f2
f2
PZT
Carrier
EOM1 EOM2
Locked by
internal
modulation
Carrier
EOM2
f1
-f2
-f1
f1=33MHz f2=166MHz
133MHz 199MHz
To MC
-f2
-f1
f2
f1
EOM1
PD
PMC transmitted
to MC
LIGO- G060231-00-R
GWAWD-VESF meeting at Elba, May 2006
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Pre-Stabilized Laser(PSL)
and 13m Mode Cleaner(MC)
BS
East Arm
ITMx
ITMy
Mode Cleaner
South Arm
PSL
ETMx
MZ PMC
MOPA126
FSS
ISS
Detection
bench
ETMy
LIGO- G060231-00-R





10W MOPA126
Frequency Stabilization Servo (FSS)
Pre-Mode Cleaner (PMC)
Intensity Stabilization Servo(ISS)
13m suspended-mass Mode Cleaner
GWAWD-VESF meeting at Elba, May 2006
7
LIGO-I type single suspension

Each optic has five OSEMs (magnet and
coil assemblies), four on the back, one on
the side


The magnet occludes light
from the LED, giving position
Current through the coil
creates a magnetic field,
allowing mirror control
LIGO- G060231-00-R
GWAWD-VESF meeting at Elba, May 2006
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The way to full RSE
Detuned dual
recycled Michelson
5 DOF lock with
offset in CARM
ETMy
RSE
Reducing
CARM offset
ITMy
PRM
BS
ITMx
ETMx
SRM
Carrier
33MHz
166MHz
LIGO- G060231-00-R
GWAWD-VESF meeting at Elba, May 2006
9
Lock acquisition procedure
towards detuned RSE
Low
gain
High
gain
TrY
PDs
POY
ITMy
166MHz
POX
13m MC
BS
ITMx
High
gain
33MHz
PRM
SP33
PO DDM
SRM
SP166
TrX
PDs
Low
gain
SP DDM
AP166
AP DDM
LIGO- G060231-00-R
GWAWD-VESF meeting at Elba, May 2006
10
Lock acquisition procedure
towards detuned RSE
Low
gain
DRMI + 2arms with offset
using DRMI
digitally normalized
1/sqrt(TrY)
High
gain
Normalization process
OSA@SP
Carrier
TrY
PDs
1
 offset
Transmitte d power
Unbalanced
166MHz
1. Avoids coupling of carrier in PRC
2. Lock with low bandwidth control
3. High cavity pole
33MHz
POY
ITMy
166MHz
Belongs to
next carrier
POX
13m MC
BS
Resonant
Off-resonant Lock
Lock point
ITMx
Belongs to
next carrier
OSA@AP
1/sqrt(TrX)
High
gain
33MHz
PRM
SP33
Q
SP166
I
SP DDM
PO DDM
SRM
TrX
PDs
Low
gain
AP166
AP DDM
LIGO- G060231-00-R
GWAWD-VESF meeting at Elba, May 2006
11
Belongs to
next carrier
Lock acquisition procedure
towards detuned RSE
1/sqrt(TrY)
Low
gain
DRMI + 2arms with offset
using digitally normalized
Normalization process
High
gain
TrY
PDs
1
 offset
Transmitte d power
1. Avoids coupling of carrier in PRC
2. Lock with low bandwidth control
3. High cavity pole
Resonant
Off-resonant Lock
Lock point
Ly=38.55m
Finesse=1235
POY
ITMy
166MHz
POX
13m MC
33MHz
BS
ITMx
Lx =38.55m
Finesse=1235
PRM
T =7%
SP33 SP166
I
SP DDM
Q
1/sqrt(TrX)
SRM
T =7%
PO DDM
High
gain
TrX
PDs
Low
gain
AP166
AP DDM
LIGO- G060231-00-R
GWAWD-VESF meeting at Elba, May 2006
12
Lock acquisition procedure
towards detuned RSE
Low
gain
Short DOFs -> DDM
CARM-> Normalized RF
DARM->Normalized RF
TrY
PDs
Design RSE
peak ~ 4kHz
Ly=38.55m
Finesse=1235
+
+
CARM with offset
DARM with no offset
Normalization process
High
gain
POX/TrX+POY/TrY
POY
ITMy
166MHz
+
CARM
-1
DARM
+
POX
13m MC
33MHz
BS
ITMx
Lx =38.55m
Finesse=1235
PRM
T =7%
SP33 SP166
SP DDM
High
gain
SRM
T =7%
PO DDM
TrX
PDs
Low
gain
AP166
AP DDM
LIGO- G060231-00-R
AP166/(TrX+TrY)
GWAWD-VESF meeting at Elba, May 2006
13
Lock acquisition procedure
towards detuned RSE
Low
gain
TrY
PDs
Reduce CARM offset
to Full RSE
Ly=38.55m
Finesse=1235
+
+
166MHz
33MHz
POX/TrX+POY/TrY
+
ITMy
13m MC
Normalization process
High
gain
CARM
-1
POX
GPR=14.5
BS
ITMx
High
gain
Lx =38.55m
Finesse=1235
PRM
T =7%
SP33 SP166
SP DDM
DARM
+
SRM
T =7%
PO DDM
TrX
PDs
Low
gain
AP166
AP DDM
LIGO- G060231-00-R
AP166/(TrX+TrY)
GWAWD-VESF meeting at Elba, May 2006
14
DARM Optical response
with fit to A.Buonanno & Y.Chen formula
40m DARM Optical Response
Radiation pressure:F = 2 P /
c
Detuned
Cavity
-> dF/dx
Optical Spring
stiffness
~107 N/m
dB mag (arb units)
Optical spring and optical
resonance of detuned RSE
were measured and fitted to
ABYC formula.
440
430
420
410
400
390
B&C
Data
380
370
1
10
BMW Z4 ~ 104 N/m
4
3
2
10
10
10
Phase (deg)
200
100
0
-100
-200
1
10
4
3
2
10
10
10
f (Hz)
Description of data, fit: http://arxiv.org/abs/gr-qc/0604078
LIGO- G060231-00-R
GWAWD-VESF meeting at Elba, May 2006
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Mathematical description for
optical spring in detuned RSE
ABYC equation:relation using two photon mode among
input vacuum a , output field b, input power and gravitational wave h

D
 b1  1  2i  C11 C12   a1 
i  1  h
  






e

2


e
 
 
D  h 
 b2  M   C21 C22   a2 
 2  SQL 
hSQL:standard quantum limit
t: transmissivity of SRM
k: input power coupling
b: GW sideband phase shift in IFO
Strain sensitivity: ratio h and a on b
hSQL  (C11  C22 ) 2 sin   (C12  C21 ) 2 cos   i

e
hn ( ) 
D1 sin   D2 cos 
2  

Optical noise: ratio between a and b
b
(C11  C22 ) 2 sin   (C12  C21 ) 2 cos 
a

M
arm cavity
a :input vacuum
b :output field
M2: C11C22-C12C21
h :gravitational wave
h
h
arm cavity
laser
ei 2 
Signal recycling
mirror
a
b
Measurement of optical response: ratio h and b
b
h

2   D1 sin   D2 cos   i
e
hSQL 
M

LIGO- G060231-00-R
a <<h; non-quantum measurement
GWAWD-VESF meeting at Elba, May 2006
16
Simple picture of optical spring in
detuned RSE
Let’s move arm differentially, X arm longer, Y arm shorter from full RSE
Wrong SRM position
Correct SRM position
BRSE
Power(W)
Power(W)
X arm
X arm
Y arm
Power(W)
Y arm
DARM (Lx-Ly)
DARM (Lx-Ly)



Power
X arm down, Y arm up
Radiation pressure
X arm down, Y arm up
Spring constant
Positive (optical spring)
LIGO- G060231-00-R
DARM (Lx-Ly)
X arm down, Y arm down
X arm up, Y arm down
X arm down, Y arm down
X arm up, Y arm down
N/A
Negative (no optical spring)
GWAWD-VESF meeting at Elba, May 2006
17
Frequency sweep of optical spring
~1900W
~270W
LIGO- G060231-00-R
GWAWD-VESF meeting at Elba, May 2006
18
CARM optical resonance
and Dynamic compensative filter
Open loop TF of CARM
Optical gain of CARM
• Optical gain (normalized
by transmitted power)
shows moving peaks
due to reducing CARM
offset.
• We have a dynamic
compensative filter
having an exactly the
same shape as optical
gain except for upside
down.
• Open loop transfer
function has no phase
delay in all CARM
offset.
LIGO- G060231-00-R
GWAWD-VESF meeting at Elba, May 2006
19
CARM optical springs
CARM optical springs at different CARM offsets
140
Arm power = 6
Arm power = 8
Arm power = 10
•Solid lines are from TCST
•Stars are 40m data
•Max Arm Power is ~80
130
CARM optical response (dB)
120
110
100
90
80
2
3
10
10
f (Hz)
LIGO- G060231-00-R
GWAWD-VESF meeting at Elba, May 2006
20
GW readout, Systems
 DC rather than RF for GW sensing
» Requires Output Mode-Cleaner to reject RF
» Offset ~ 1 picometer from dark fringe can tune from 0
to 80 deg with 0-100 mW of fringe offset power
Noise Source
Laser frequency
noise
Laser amplitude
noise
RF readout
DC readout
~10x more
sensitive
Less sensitive
since carrier
is filtered
Sensitivity identical for
frequencies below ~100 Hz; both
driven by technical radiation
pressure
10-100x more
sensitive above
100Hz
Carrier is
filtered
Laser pointing noise
Sensitivity essentially the same
Oscillator phase
noise
-140 dBc/rtHz at
100 Hz
LIGO- G060231-00-R
fringe
offset
β
Loss mismatch
Mode matching
telescope
OMC
DC PD
NA
GWAWD-VESF meeting at Elba, May 2006
21
Squeezing Tests at the 40m
 Go from MIT group brought an audio frequency squeezer
to 40m, and injection of squeezed vacuum will be tested.
 SHG, OPO ready, homodyne detector being developed.
 Time to take steps toward injection to 40m interferometer
» DRSE configuration will be tested
» LIGO-like control systems for eventually porting squeezing technology
to long baseline ifos
SHG
2W from
MOPA
Squeezed
vacuum
to IFO
OPO
LIGO- G060231-00-R
GWAWD-VESF meeting at Elba, May 2006
22
Other ideas
 Low frequency-low frequency RF modulation
scheme (40m:33-55MHz, AdLIGO:27-45MHz)
instead of LF-HF RF
 Alignment Sensing and Control (ASC) on detuned
RSE with LF-LF RF modulation
 ASC with lighter mirrors in order to investigate pitch
and yaw optical springs
 Variable band operation using SRC error signal
normalized by LF f2 power
LIGO- G060231-00-R
GWAWD-VESF meeting at Elba, May 2006
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