Sensing and Controlofan Interferometer Gravitational Wave
Detector TAMA300
Koji Arai on behalf of the TAMA project
National Astronomical Observatory of Japan

TAMA300: Interferometer GW detectorl TAMA300:
A 300-m Power-recycled Fabry-Perot Michelson Interferometer
Site: National Astronomical Observatory of Japan(Mitaka, Tokyo)

l Operation of TAMA300
Fabry-Perot Michelson:
1999~2001
Power Recycling:
2001~Presentl This talkLength sensing and control
Lock acquisition
Alignment control

Optical configuration of TAMA300

300m
FP cavity
Injection-locked
Nd:YAG Laser
P=8W

10-m
mode cleaner
F~1700fc=4.4kHz

300m
FP cavity

P=2W

RRM=0.5

F~500
fc=500Hz

RFPMI=0.9

Optical configuration of TAMA300

300m
FP cavity
Injection-locked
Nd:YAG Laser
P=8W

10-m
mode cleaner
F~1700fc=4.4kHz

F~500
fc=500Hz300m
FP cavity

P=2W

RRM=0.5

RFPMI=0.9
o Intentionally low RRM

G=4.6

o Shorter arm=> higher finesse=> lower reflectanceLength sensing and control
l Recycled Fabry-Perot Michelson Interferometer4 longitudinal d.o.f. to be controlled~ The optical cavities and the Michelson interferometermust be on the operating point

L−= L2−L1
L+= L2+L1
l− = l2 − l1
l+ = l2 + l1

L2
l2
l1

L1

Length sensing and control ~ for lock acquisitionl Based on the PDH technique and Schunupp modulation- single phase modulation at 15MHz- 3rd harmonic demodulation
at the reflection port
- PDH technique at the pick off ports
δ L2
Phase Modulators
15.235 11.97
MHz MHzδ l+ fδ l− fPickoff
Signals

x3

x3

3rd
harmonicdemod.

δ L1

Length sensing and control ~ for lock acquisitionl Based on the PDH technique and Schunupp modulation- single phase modulation at 15MHz- 3rd harmonic demodulation
at the reflection port
- PDH technique at the pick off ports
δ L2
Phase Modulators
15.235 11.97
MHz MHzδ l+ fδ l− fPickoff
Signals

x3

x3

3rd
harmonicdemod.

δ L1

Length sensing and control ~ for lock acquisitionl Based on the PDH technique and Schunupp modulation- single phase modulation at 15MHz- 3rd harmonic demodulation
at the reflection port
- PDH technique at the pick off ports
δ L2
Phase Modulators
15.235 11.97
MHz MHzδ l+ fδ l− fPickoff
Signals

x3

x3

3rd
harmonicdemod.

δ L1Length sensing and control ~ for lock acquisitionl Based on the PDH technique and Schunupp modulation- single phase modulation at 15MHz- 3rd harmonic demodulation
at the reflection port
- PDH technique at the pick off ports
δ L2
Phase Modulators
15.235 11.97
MHz MHzδ l+ fδ l− fPickoff
Signalsx3x3

3rd
harmonicdemod.

δ L1

Lock acquisition
State 1
SB1
CA

CA G0=0, under-coupled
SB1 G1=0, under-coupled

State 2

CA G0=0.18, under-coupled
SB1 G1=4.4, over-coupled

State 3

CA G0=0.51, under-coupled
SB1 G1=4.4, over-coupled

Drastic increase of the internal power
Change of the couplings to the IFO=> change in optical gains and signal sign

State 4

CA G0=4.6, over-coupled
SB1 G1=4.4, over-coupled3rd harmonic demodulation
lPhotocurrent at the 3fm~ beating of SB2 and SB-1
modulation
sidebands

K. Arai, et al,Phys. Lett. A 273 (2000) 15
K. Arai, et al,Class. Quantum Grav. 19 (2002) 1843

3fm

SB-3 SB-2 SB-1 CarrierSB1 SB2 SB3

frequencyofelectric fieldlEffect of SB2s are emphasized at the reflection port
Signal with fm demod. and 3fm demod. ~ order of m and m3
SB2s are not resonant=> reflectance is ~1CA, SB1s, and SB3s are resonant => reflectance can be low

3rd harmonic demodulationl Merit of 3fm demod~ robust extraction of δl+ and δl−Contribution of carrier audio-sidebands (~ δL+)=> Reduced

Amplitudes of the δl+ and δl− signals=> Less dependent on the couplings of CA and SB1=> Less variation during lock acquisition
Signs of the signals=> Independent from the optical parameters=> Invariant during lock acquisition

Extracted signal (calculation)lWell-diagnalized signals
PortDark
BrightBrightBrightBrightDemod Phase
Lfm
Q1fm
I
1.5e-43fm
Q
1.0e-2fm
Q
1.5e-23fm
I
1.5e-4lShot noise limit
Port

Demod PhaseL+
3.0e-41
2.3e-26.2e-16.5e-2l3.0e-3
6.1e-61
1
1.2e-3l+
1.0e-68.4e-53.6e-2
1.6e-3
1

Shotnoise level (m/Hz1/2)

Dark

fm

Q

L-

1.2 x 10-19 =4.0 x 10-22 1/Hz-1/2

Pick-off

fm

I

L+

1.6 x 10-19 =1.5 x 10-7 Hz/Hz-1/2

Bright3fm

Ql-

1.4 x 10-14

for lock

Brightfm

Ql-

2.0 x 10-16

for operation

Bright3fm

Il+

2.8 x 10-15

Gain variation / Sign flip (Recycling1)
3fm signals
dl+
x 0.82

1.0
RecycledMichelson

Optical gain

0.5

0.0

RecycledMichelson+
One arm-0.5

dl-

fm signals
dl+
x −0.023
Recycled
Fabry-Perot
Michelson-1.0
23Statex 0.46dl-

x −0.76

4No sign flip and less gain changes with 3fm signals~ no need of adaptive servo system (variable gain adj., dynamic sign change)

Length sensing and control ~ for lock acquisitionl Based on the PDH technique and Schunupp modulation- single phase modulation at 15MHz- 3rd harmonic demodulation
at the reflection port
- PDH technique at the pick off ports
δ L2
Phase Modulators
15.235 11.97
MHz MHzδ l+ fδ l− fPickoff
Signalsx3x3

3rd
harmonicdemod.

δ L1

Mixing of arm Pound-Drever-Hall signalsl Power Recycling~ Arm length signals are mixed
Power recycling gain of 4.5
Vpo1

10.5

dL1

0.5

1

dL2

=Vpo2

~ still enough independent for lock acquisition~ would be a problem with more recycling gain
G=10 => mixing of 0.85

Lock acquisitionl Typically the lock is acquired within minutes~ with good alignment
5State4

3teta
Sta

1te

232S

Power recycling gain

4--- Inline arm--- Perpend. arm

0102030
Time [Second]4050

Alignment sensing and controll Wave front sensing technique- mode cleaner cavity- arm cavities- recycling mirror
QPDs
Gouy phasetelescopes

15.235 11.97
MHz MHzQPDs

QPDs

Gouyphasetelescopes

Lock acquisitionl Alignment control
for the arm, UGF: 5~10Hz, for the RM, UGF: ~10mHz
5Power recycling gain

4--- Inline arm--- Perpend. arm
Alignment
Control ON3210102030
Time [Second]4050

Length sensing and control ~ for low noise model Common/differential separated control
Dark port=> Arm differential
Reflection port=> Arm common=> Michelson

Bright port 3f=> Recycling Mirror

Phase Modulators
15.235 11.97
MHz MHz6W

δ l+ fδ L+δ l−x3

δ L−

Summaryl Length/Alignment sensing for TAMA300- Based on the PDH technique and the Schnupp modulation- Key features for lock acquisition:
3fm demodulation for dl+ and dlPO signals for the arms
- Alignment control
for the MC, the arms and the recycling mirror- Switching to low noise control signals