amaldi conference, june 2005 1 lock acquisition scheme for the advanced ligo optical configuration...

Amaldi conference, June 2005 1

Lock acquisition schemefor the Advanced LIGO

optical configuration

Amaldi conferenceJune24, 2005

O. Miyakawa, Caltechand the 40m collaboration


Caltech 40 meter prototype interferometer

Objectives Develop lock acquisition procedure of detuned Resonant Sideband

Extraction (RSE) interferometer, as close as possible to AdLIGO optical design

BSPRM SRM

X arm

Darkport

Brightport

Y arm

Characterize noise mechanisms Verify optical spring and optical

resonance Develop DC readout scheme Extrapolate to AdLIGO via

simulation


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


5 DOF for length control

: L=( Lx Ly) / 2

: L= Lx Ly

: l=( lx ly) / 2

=2.257m: l= lx ly = 0.451m

: ls=( lsx lsy) / 2

=2.15m

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 cavity

MichelsonSignal recycling cavity

Laser

ETMy

ETMx

ITMy

ITMxBS

PRM

SRM

SPAP

PO

lx

ly

lsx

lsy

Lx =38.55m

Finesse=1235

Ly=38.55m

Finesse=1235Phase Modulationf1=33MHzf2=166MHz

T =7%

T =7%

GPR=14.5


Differences betweenAdvLIGO and 40m prototype

100 times shorter cavity length Arm cavity finesse at 40m chosen to be = to AdvLIGO ( = 1235 )

» Storage time is x100 shorter.

Control RF sidebands are 33/166 MHz instead of 9/180 MHz» Due to shorter PRC length, less signal separation.

LIGO-I 10-watt laser, negligible thermal effects» 180W laser will be used in AdvLIGO.

Noisier seismic environment in town, smaller stack» ~1x10-6m at 1Hz.

LIGO-I single pendulum suspensions are used» AdvLIGO will use triple (MC, BS, PRM, SRM) and quad (ITMs, ETMs)

suspensions.


Lock acquisition procedure towards detuned RSE

ITMy

ITMxBSPRM

SRM

ETMx

ETMy

Shutter

Shutter

Carrier33MHz166MHz

DRMI using DDM Off-resonantarms using DC lock

(POX/TrX),(POY/TrY)

SP166/PRC,AP166/PRC

(POX/TrX) + (POY/TrY), (POX/TrX) – (POY/TrY)

(TrX + TrY), (TrX – TrY) / (TrX + TrY)

Ideas for armcontrol signal

RSE

Done In progressDone


DRMI lock using double demodulation with unbalanced sideband by detuned cavity

August 2004August 2004DRMI locked with carrier resonance (like GEO configuration)DRMI locked with carrier resonance (like GEO configuration)November 2004November 2004DRMI locked with sideband resonance (Carrier is anti resonant preparing for RSE.)DRMI locked with sideband resonance (Carrier is anti resonant preparing for RSE.)

Carrier

33MHz

Unbalanced166MHz

Belongs tonext carrier

Belongs tonext carrier

Carrier33MHz166MHz

ITMy

ITMxBS

PRM

SRM

OSA DDM PD

DDM PD

DDM PD

Typical lock acquisition time : ~10secLongest lock : 2.5hour


Struggling lock acquisition for arm cavities

Problems

1. High recycling gain of ~15 produces 94% coupling between two arms.

2. Very high coupled finesse of ~18000.

3. Slow sampling rate of 16kHz for direct lock acquisition.

So, we have two steps

1. Each arm lock using transmitted light with DC offset. …done

2. Reduce offset to have full resonance of carrier. …in progress


• Error signal is produced by only transmitted light as

• Smaller coupling• Wider linear range than RF error signal.

Off-resonant DC lock scheme for arm cavity

Off-resonantLock point

Resonant Lock

offsetpower dTransmitte

1


All 5 degrees of freedom under controlledwith DC offset on L+ loop

Both arms locked with DRMIBoth arms locked with DRMI Lock acquisition time ~1 minLock acquisition time ~1 min Lasts ~ 20 minLasts ~ 20 min Can be switched to Can be switched to

common/differential controlcommon/differential controlLL- : AP166 with no offset- : AP166 with no offsetLL+ : Trx+Try with DC offset+ : Trx+Try with DC offset

Yarm lockXarm lock

Arm power

Error signal

Ideal lockpoint

Offset lockOffset lock

Have started trying toreduce offset from L+ loop

But…


Peak changing due to reduction of offset

• Peak started from 1.6kHz and reached to ~450H.

• This peak introduces phase delay around unity gain frequency.


CARM at 218 pm offset (~locking point)

-100

-90

-80

-70

-60

-50

-40

-30

-20

-10

0

1 10 100 1000 10000 100000-200

-150

-100

-50

0

50

100

150

200

dB

Ph

as

e [

De

g]

f [Hz]

CARM optical response, CARM offset at 218 pm

SP33I n1 : dB SP33I n1 : Phase [Deg]

NPTRX n5 : dB NPTRX n5 : Phase [Deg]

UnityGainFrequency


CARM at 118 pm offset

-100

-80

-60

-40

-20

0

20

1 10 100 1000 10000 100000-200

-150

-100

-50

0

50

100

150

200

dB

Ph

as

e [

De

g]

f [Hz]

CARM optical response, CARM offset by 118 pm



UnityGainFrequency


CARM offset at 59 pm (losing lock)

-100

-80

-60

-40

-20

0

20

40

1 10 100 1000 10000 100000-200

-150

-100

-50

0

50

100

150

200

dB

Ph

as

e [

De

g]

f [Hz]

CARM optical response, CARM offset by 59 pm



UnityGainFrequency


L- optical gain with RSE peak

•Optical gain of L- loopDARM_IN1/DARM_OUT,divided by pendulum transfer function

• No offset on L- loop• 150pm offset on L+ loop

•Optical resonance of detuned RSE can be seen around the design RSE peak of 4kHz.•Q of this peak is about 6.

Design RSEpeak ~ 4kHz


DARM, operating point

-40

-30

-20

-10

0

10

20

30

40

50

60

1 10 100 1000 10000 100000 0

20

40

60

80

100

120

140

160

180

dB

Ph

ase

[D

eg

]

f [Hz]

DARM optical response, CARM at 218 pm offset

APGW n2 : dB APGW n2 : Phase [Deg]



Summary

All 5DOFs are locked with some offset on L+. RSE detuning peak was seen. L+ loop has a detuning peak with DC offset and it

introduces phase delay around unity gain frequency with reducing offset.

Fortunately, Advanced LIGO will not have L+ peak problem !

Cavity pole of single arm is around 16Hz from the beginning, far below from unity gain frequency of L+ loop around 300Hz.

Fast frequency control or proper compensative digital filter may fix this problem for 40m.

Hope we succeed in locking full RSE very soon!


DC Readout at the 40m DC Readout eliminates several sources of technical noise

(mainly due to the RF sidebands): – Oscillator phase noise – Effects of unstable recycling cavity. – The arm-filtered carrier light will serve as a heavily

stabilized local oscillator. – Perfect spatial overlap of LO and GW signal at PD.

DC Readout has the potential for QND measurements, without major modifications to the IFO.

We can use a 3 or 4-mirror OMC to reject RF sidebands.» Finesse ~ 500, In-vacuum, on a seismic stack.

The DC Detection diode» an aluminum stand to hold a bare photodiode, and

verified that the block can radiate 100 mW safely.

from SRM

From SRM

amaldi conference, june 2005 1 lock acquisition scheme for the advanced ligo optical configuration...

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