1LIGO-G060396-00-R

Is it possible to acquire lock with radiation pressure? Is it possible to control alignment with radiation pressure? Optical spring in ASC? Do we need test mass actuator for ASC? both ETM and ITM? Is the actuator dynamic range enough? Noise performance?

Osamu Miyakawa, Hiroaki YamamotoCaltech

8/14/2006 LSC meeting at LSU

Time domain simulation fora FP cavity with AdLIGO parameters on E2E

2LIGO-G060396-00-R

What implemented

AdLIGO Quad suspension (Mark’s model 03/31/2006)

Local damping (6 DOFs of M0)

Seismic motion and optical table motion on X,Y, tY and tZ (length, side, pitch and yaw)

3995m FP single cavity with AdLIGO parameters

» ROC = 2076m for both ITM, ETM test mass

» Full laser power inside cavity = 0.73MW

Radiation pressure force on length and alignment

Shot noise and radiation pressure noise

Length control for M3 through M1, M2, M3

M3 alignment control through M2 using WFS

Electronic noise of WFS PD

Main Ref.

Top mass (M0)

Upper Intermidiatemass (M1)

Penultimatemass (M2)

Test mass(M3)

XY

Z

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Optics

QuadSuspension

ETMSeismicmotion

PDs

QuadSuspension

ETMSeismicmotion

FeedbackfiltersLaser

E2E

FP summation cavity

Rdiationpressure

Rdiationpressure

Mainmass

Ref.mass

Actuator

LocalDamping

4LIGO-G060396-00-R

100

101

10-2

100

Open loop TF

Ga

in

100

101

10-2

100

Suspenstoin TF

Ga

in

rawdamped

100

101

10-1

100

101

102

Feedback filter TF

frequency [Hz]

Ga

in

Local damping

Main Ref.

M0

M1

M2

M3

6(6)

0(3)

0(3)

0(0)

Damped DOFs(OSEM DOFs)

Example M0: pitch

Zero @ 0HzPole @ 10,10Hz

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Local damping: impulse response

Example M0: pitch

10 15 20 25-8

-6

-4

-2

0

2

4

6

8x 10

-6

Time[s]

Pitc

h o

f To

p m

ass

[ra

d]

Pitch impulse response

E2E simulation Measured data

6LIGO-G060396-00-R0 10 20 30-1.5

-1

-0.5

0

0.5

1

1.5

2

2.5x 10

-5

Time[s]

[m]

Position

0 10 20 30-2

-1.5

-1

-0.5

0

0.5

1x 10

-5

Time[s]

[ra

d]

Pitch

ITM.m0ITM.m1ITM.m2ITM.m3ETM.m0ETM.m1ETM.m2ETM.m3

0 10 20 300

1

2

3

4

5

6

7

8x 10

5

Time[s]

[W]

Power

Quad suspension withradiation pressure (length)

ITM ETM

Radiationpressure

LSC

LSC

LSC

8e-6 rad

1.2e-5 m

LSC only, no ASC

Only TEM00; misalignment not break lock

Test masses are pushed by radiation pressure.

ETM test mass is pushed back by LSC keeping distance between test masses.

Position shift ~10 wave length

Angle shift ~10rad

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Lock acquisition with radiation pressure

60nm/sec :enough slow to acquire lock for LSC by Matt Evans

Radiation pressure and alignment incleded

Full power : 0.7MW

Lock can be acquired with less than few kW

» Is it possible such low power? Offset lock used at 40m? ->Optical spring

Needs Monte Carlo simulation

Locked

Locked

No lock

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0 1 2 3 4 50

1

2

3

4

5

6

7

8x 10

4

Time[s]

[W]

Power

TEM00TEM01(pit) x10TEM10(yaw) x10

0 1 2 3 4 5-3

-2

-1

0

1

2

3x 10

-6

Time[s]

[m]

Position

0 1 2 3 4 5-2

-1.5

-1

-0.5

0

0.5

1x 10

-6

Time[s]

[ra

d]

Pitch

ITM.m0ITM.m1ITM.m2ITM.m3ETM.m0ETM.m1ETM.m2ETM.m3

Alignment instability with no ASC

After lock acquisition, input power increased with no ASC.

Pitch motion due to Radiation pressure breaks lock with 10%(70kW) of full power if there is no ASC

Lost lock

9LIGO-G060396-00-R0 10 20 30-1.5

-1

-0.5

0

0.5

1

1.5

2

2.5x 10

-5

Time[s]

[m]

Position

ITM.m0ITM.m1ITM.m2ITM.m3ETM.m0ETM.m1ETM.m2ETM.m3

0 10 20 30-12

-10

-8

-6

-4

-2

0

2x 10

-6

Time[s]

[ra

d]

Pitch

0 10 20 300

1

2

3

4

5

6

7

8x 10

5

Time[s]

[W]

Power

Test mass alignment control through M2with radiation pressure

ITM ETM

Radiationpressure

LSC

LSC

LSC

1.3e-5 m

ASC

ASC

ASC

ASC

Control M3 through M2

f 3 filter

Boost at 2Hz

10Hz control band width

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Two modes of optical instability

Differential : stable -> spring

Common : unstable -> no spring

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102

103

104

105

106

107

Pitch opto-mechanical(suspenstion) TF

Gai

n

0Wcommdiff

100

101

-180-135

-90-45

04590

135180

Frequency [Hz]

Pha

se[d

eg]

102

103

104

105

106

107

yaw opto-mechanical(suspenstion) TF

Gai

n

0Wcommdiff

100

101

-180-135

-90-45

04590

135180

Frequency [Hz]P

hase

[deg

]

Opt-mechanical (suspension) TF

TF from M2 actuator to WFS error signal, simulated in time domain.

Low frequency gain and peak are suppressed.

» Needs compensating gain for full power

Optical spring in differential mode at 4.5Hz for pitch and 4.1Hz for yaw.

Control BW must be higher than optical spring frequency.

Optical spring Optical spring

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101

102

103

104

ASC pitch open loop TF

Gai

n

0Wcommdiff

100

101

-180-135

-90-45

04590

135180

Frequency [Hz]

Pha

se[d

eg]

Open loop TF of ASC

10Hz control band width

Gain in low frequency is suppressed a lot by radiation pressure

101

102

103

104

ASC yaw open loop TF

Gai

n

0Wcommdiff

100

101

-180-135

-90-45

04590

135180

Frequency [Hz]P

hase

[deg

]

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Noise performance

Residual RMS: <10-9 rad (depends on servo) of 10-9rad requirement

Actuation torque(force): 3x10-5 Nm (1x10-4 N) on M2 OSEM (max 20mN)

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100

102

10-16

10-14

10-12

10-10

10-8

ITM pitch

Pitc

h [r

ad

/sq

rt(H

z)]

Frequency [Hz]10

010

210

-16

10-14

10-12

10-10

10-8

ITM yaw

Ya

w [r

ad

/sq

rt(H

z)]

Frequency [Hz]

GroundTableTest massWFS

100

102

10-16

10-14

10-12

10-10

10-8

ETM pitch

Pitc

h [r

ad

/sq

rt(H

z)]

Frequency [Hz]10

010

210

-16

10-14

10-12

10-10

10-8

ETM yaw

Ya

w [r

ad

/sq

rt(H

z)]

Frequency [Hz]

Noise performance in spectra

Spectrum depends on seismic noise model.

Length to pitch coupling is not ignorable, but can be avoided using unbalance of OSEM.

High frequency is limited by shotnoise at 10-14

rad/rHz with 100mW input(25mW for each quadrant).

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0 1 2 3 4 5

1

2

3

4

5

6

7

8

9

10x 10

4

Time[s]

[W]

Power

0 1 2 3 4 5-0.03

-0.02

-0.01

0

0.01

0.02

0.03

Time[s]

[N]

Actuation force on M2

ITM-pitITM-yawETM-pitETM-yaw

Electronic noise with low power

Full power: 0.7MW with electronic noise of 10-6rad/V, 100mVmax, 10nV/rHz

» 10-14rad/rHz (same level as shotnoise), force: 3x10-4Np-p (maximum:20mN)

Low power: 1kW for lock acquisition, 7x10-4rad/V, 100mVmax, 10nV/rHz

» 7x10-12rad/rHz, force: 20mNp-p(maximum:20mN) -> OSEM saturation

Lockedwith 1kW

WFS ON

Startincreasing

power

10% of fullpower

M2 OSEMDynamicrange

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100

101

102

10-15

10-14

10-13

10-12

10-11

10-10

10-9

ETM pitch: error point

Ca

libra

ted

WF

S s

ign

al [

rad

/sq

rt(H

z)]

Frequency [Hz]

Pit Lopwer(1kW)Pit Full power(0.7MW)Yaw Lopwer(1kW)Yaw Full power(0.7MW)

100

101

102

10-12

10-10

10-8

10-6

10-4

10-2

ETM pitch: feedback point

Act

ua

tion

forc

e [N

/sq

rt(H

z)]

Frequency [Hz]

Pit Lopwer(1kW) PSDPit Lopwer(1kW) RMSYaw Lopwer(1kW) PSDYaw Lopwer(1kW) RMS

Electronic noise with low power

Feedback Penultimate mass(M2) and test mass(M3) for both ITM and ETM?

Low/High gain WFS?

Variable transimpedance of factor sqrt(700)?

» Same level as shotnoise of low power case

Pole around 30Hz?

M2 OSEMDynamicrange

ElectronicNoiseEnhancement

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0 1 2 3 4 5

1

2

3

4

5

6

7

8

9

10x 10

4

Time[s]

[W]

Power

0 1 2 3 4 5-0.03

-0.02

-0.01

0

0.01

0.02

0.03

Time[s][N

]

Actuation force on M2

ITM-pitITM-yawETM-pitETM-yaw

2-pole at 30Hz

Seems stable

Lockedwith 1kW

WFS ON

Startincreasing

power

10% of fullpower

M2 OSEMDynamicrange

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Conclusion

Is it possible to acquire lock with radiation pressure? » Yes, with less than few kW

Is it possible to control alignment with radiation pressure? » Yes, with 10Hz control band-width

Optical spring in ASC? » Yes, 4-5Hz

Do we need test mass actuator for ASC? both ETM and ITM? » No for full power, penultimate mass actuator enough, but might be necessary for low power

Is the actuator dynamic range enough? » Yes for full power: 1mN of 20mN, but No for low power: 20mN of 20mN -> low-pass filter

around 30Hz Noise performance?

» < 10-9 rad

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Next step

Unbalance on OSEM

Miss-centering

Another g-factor

Monte-Carlo lock acquisition test

Lock acquisition for full DRFPMI case

» simulation time : real time = 10 : 1 for single FP cavity

= 200 : 1 for DRFPMI with LSC only

= 400000 : 1 for DRFPMI with ASC

->needs summation DRMI for alignment