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Discussion of the Advanced LIGO design and sensitivity

Denis Martynov,Massachusetts Institute of Technology

Baikal School on High Energy Physics and Astrophysics July 14, 2016

LIGO Laboratory2

Overview

LIGO optical design Broadband stationary noises

Environmental noises Fundamental noise sources Technical noise sources

Future plans and goals

3

Michelson interferometer

» Measures differential length of two arms using the detector at the antisymmetric port

LIGO Laboratory4

Optical layout

4 km

100 kW

1064 nm

Laser

22W800W

85mW

25mW9MHz

oscillator

5

45MHz

5 longitudinal degrees of freedom• differential arm (GW) • common arm • Michelson interferometer • power recycling cavity • signal recycling cavity

10�14 m

10�12 m

10�6 mGround motion

5

LIGO optical design

» We need nice, robust and low noise instrument

» Quantum noise» Resonators

PD2

Laser

2W

PD1

servo

6

Classical picture of light

100 102 104 106

Frequency, Hz

10-10

10-9

10-8

10-7

10-6

10-5

10-4

Mag

nitu

de, W

/Hz1/

2

Free running laserPD1PD2

P = AA⇤ = (A+ acl)(A⇤ + a⇤cl)

Pac = Aa⇤cl + A⇤acl

where is a static DC fieldis an oscillating AC field (signal or noise)

A

acl

A

PD2

Laser

2W

PD1

servo

7

Classical picture of light

100 102 104 106

Frequency, Hz

10-10

10-9

10-8

10-7

10-6

10-5

10-4

Mag

nitu

de, W

/Hz1/

2

Free running laserPD1PD2Ap

2

Ap2

aclp2

aclp2

aclA

P1 =1

2(Aa⇤cl + A⇤acl)

P2 =1

2(Aa⇤cl + A⇤acl)

PD2

Laser

2W

PD1

servo

8

Classical picture of light

Ap2

Ap2

aclp2

aclp2

aclA

P1 =1

2(Aa⇤cl + A⇤acl)

P2 =1

2(Aa⇤cl + A⇤acl)

100 102 104 106

Frequency, Hz

10-10

10-9

10-8

10-7

10-6

10-5

10-4

Mag

nitu

de, W

/Hz1/

2

Free running laserPD1PD2

PD2

Laser

2W

PD1

servo

9

Classical picture of light

Ap2

Ap2

aclp2

aclp2

aclA

P1 =1

2(Aa⇤cl + A⇤acl)

P2 =1

2(Aa⇤cl + A⇤acl)

100 102 104 106

Frequency, Hz

10-10

10-9

10-8

10-7

10-6

10-5

10-4

Mag

nitu

de, W

/Hz1/

2

Free running laserPD1PD2

PD2

Laser

2W

PD1

servo

10

Classical picture of light

Ap2

Ap2

aclp2

aclp2

aclA

P1 =1

2(Aa⇤cl + A⇤acl)

P2 =1

2(Aa⇤cl + A⇤acl)

100 102 104 106

Frequency, Hz

10-10

10-9

10-8

10-7

10-6

10-5

10-4

Mag

nitu

de, W

/Hz1/

2

Free running laserPD1PD2

PD2

Laser

2W

PD1

servo

11

Quantum picture of light

Ap2

Ap2

A

100 102 104 106

Frequency, Hz

10-10

10-9

10-8

10-7

10-6

10-5

10-4

Mag

nitu

de, W

/Hz1/

2

Free running laserPD1PD2

a1

a2

a1 + a2p2

a1 � a2p2

P1 = Pcl,1 +1

2(A(a⇤1 + a⇤2) + A⇤(a1 + a2))

P2 = Pcl,2 +1

2(A(a⇤1 � a⇤2) + A⇤(a1 � a2))

PD2

Laser

2W

PD1

servo

12

Quantum picture of light

Ap2

Ap2

A a1

a2

a1 + a2p2

a1 � a2p2

P1 = Pcl,1 +1

2(A(a⇤1 + a⇤2) + A⇤(a1 + a2))

P2 = Pcl,2 +1

2(A(a⇤1 � a⇤2) + A⇤(a1 � a2))

100 102 104 106

Frequency, Hz

10-10

10-9

10-8

10-7

10-6

10-5

10-4

Mag

nitu

de, W

/Hz1/

2

Free running laserPD1PD2Shot noise

p2h⌫Pdc

13

Quantum noise in the Michelson interferometer

Laser

DC power at the anti-symmetric portAin

Aas

Pas = Pin sin2 �, where

� = 2⇡x0

�

⌧ 1 is a small detuning

Optical transfer functiondPas

dx

=

Pin

�

4⇡ sin� cos�

Shot noise in units of length is

x

shot

=�

2⇡ cos�

rh⌫

2Pin

= 4.34⇥ 10�18

r125W

P

in

mpHz

ain

aas

14

Fabry-Perot interferometer

Laser

AinAtrAres

Ti Te

Equation of for the intracavity field

Build-up

Ares =p

TiAin +p1� Ti

p1� Te

p1�XAres

b =Ares

Ain=

2pTi

Y, where

Y = Ti + Te +X is the total loss in the cavity

15

Optimal design

» Maximize power in the arms» Minimize power going through the substrates» Filter laser noises» Optimize response in the frequency range

10Hz-10kHz

Laser

Power in the arms is limited by the optical losses1

2GprcGarm =

1

X

Gprc Garm

Garm

LIGO Laboratory16

Quantum noise

101 102 103 104

Frequency, Hz

10-21

10-20

10-19

10-18

10-17

Mag

nitu

de, m

/Hz1/

2 Michelson typeInitial LIGO type

LIGO Laboratory17

Quantum noise

101 102 103 104

Frequency, Hz

10-21

10-20

10-19

10-18

10-17

Mag

nitu

de, m

/Hz1/

2 Michelson typeInitial LIGO type

?

Laser

18

Quantum radiation pressure noise

Power fluctuations in the armAin

aas

Pm =?

Laser

19

Quantum radiation pressure noise

Power fluctuationsAin

vacuum field also resonates and drives suspended mirrorsaas

Pm =p

2h⌫Parmb

Fm =2Pm

c

xm =Fm

M!

2

LIGO Laboratory20

Quantum noise

101 102 103 104

Frequency, Hz

10-21

10-20

10-19

10-18

10-17

Mag

nitu

de, m

/Hz1/

2 Michelson typeInitial LIGO type

?

21

Fabry-Perot interferometer

Laser

ares(t) =p

Tiain(t) + (1� Y

2)ares(t� ⌧)

Equation for the intracavity field

where is the round trip time⌧ =2L

c

⌧ ares +Y

2ares =

pTiain

Solution to this equation is

ares(!) =

pTiain(!)

i!⌧ + Y2

100 102 104

Frequency, Hz

10-2

10-1

100

Mag

nitu

de, W

/W

Y c

8⇡L

LIGO Laboratory22

Advanced LIGO

4 km

100 kW

1064 nm

Laser

22W800W

85mW

25mW9MHz

oscillator

5

45MHz

New mirror

LIGO Laboratory23

Quantum noise

101 102 103 104

Frequency, Hz

10-21

10-20

10-19

10-18

10-17M

agni

tude

, m/H

z1/2 Michelson type

Initial LIGO typeAdvanced LIGO type

24

Noises

» We need to make noises as low as possible» Environmental noises» Fundamental noises» Technical noises

LIGO Laboratory25

Environmental noises

Ground vibrations Gravity gradients Acoustic noise

26

Ground motion

» the motion of the optical table is actively controlled» this motion is passively filtered using multistage

suspensions» gravity gradients are caused by the motion of

chambers, people and the ground

27

Ground motion

10−1 100 10110−14

10−13

10−12

10−11

10−10

10−9

10−8

10−7

10−6

10−5

10−4

Frequency, Hz

Dis

plac

emen

t, m

/Hz1/

2

Ground motion in summerGround motion in winterHAM table in summerHAM table in winterBSC table in summerBSC table in winterGS13 noise

28

Suspension transfer function

10−1 100 10110−7

10−6

10−5

10−4

10−3

10−2

10−1

100

101

Mag

nitu

de (a

bs)

Frequency (Hz)

QUADBSFMHLTSHSTS

LIGO Laboratory29

Scattered light noise

Light scattered out from the main beam gets modulated in phase and amplitude and partially scatters back into the main beam.

20 100 1000 5000Frequency, Hz

10-22

10-21

10-20

10-19

10-18

Dis

plac

emen

t, m

/Hz1/

2

GW signal channelEnd X bulidingEnd Y buildingCorner Station Center and Output AreaCorner Station Input AreaLaser Enclosure

Input test mass

4km

1m

End test mass

LIGO Laboratory30

Fundamental noises

In theory, fundamental noises should limit sensitivity of the instrument

Fundamental sensing noises: Shot noise Residual gas noise

Fundamental displacement noises: Thermal noises Quantum radiation pressure noise

31

Thermal noise

» LIGO operates at room temperature» Thermal motion is proportional to» Arises from finite losses present in

mechanical systems (need high Q)» Thermal motion of the atoms in

suspension fibers moves the mirror

pkT

LIGO Laboratory32

Fundamental noises

101 102 103 104

Frequency [Hz]

10-22

10-21

10-20

10-19

10-18D

ispl

acem

ent [

m/

Hz]

Quantum noiseSeismic noiseGravity GradientsSuspension thermal noiseCoating Brownian noiseCoating Thermo-optic noiseSubstrate Brownian noiseExcess GasTotal noise

LIGO Laboratory33

Technical noises

Technical nosies in the arm cavities include Laser noises Actuator electronics Residual gas in the chambers Angular motion of test masses Charging noise

Auxiliary longitudinal and angular degrees of freedom Input-output port noises

Laser phase and amplitude noises Beam jitter

34

Laser noises

Ideal laser field

Real laser field fluctuates in amplitude and phase

This noise couples to the gravitational wave channel

A(t) = A0sin(!t+ �0)

A(t) = A0(1 +An(t))sin(!t+ �0 + �n(t))

35

Auxiliary degrees of freedom

4 km

100 kW

1064 nm

Laser

22W800W

85mW

25mW9MHz

oscillator

5

45MHz

» Longitudinal from the corner station

» Angular from the arm cavities

LIGO Laboratory36

Low frequency spectrum

LIGO Laboratory37

High frequency spectrum

LIGO Laboratory38

Conclusions

Optical design of the Advanced LIGO is optimized for the frequency range 10Hz - 10kHz

There is an unknown noise source at 20Hz - 100Hz Above 100Hz sensitivity is limited by quantum noise Future goals include the upgrade of the current facility

and construction of a longer facility

https://dspace.mit.edu/handle/1721.1/28646 http://thesis.library.caltech.edu/8899/

39

LIGO Scientific Collaboration

LIGO Laboratory40

Extra slides

LIGO Laboratory41

Charging noise

If mirror surfaces are charged, ambient electric fields couple to gravitational wave channel

Ion gun was developed to discharge the mirrors

Reactionmass

Electrodes

Ringheater

Suspensioncage

HRcoating

Testmass

LIGO Laboratory42

Intensity noise coupling

Laser noises are filtered at 0.6 Hz by the coupled cavity pole. Extra coupling mechanism comes from high-order modes

100 300 600 1000 2000Frequency, Hz

-60

-55

-50

-45

-40

-35

-30

Mag

nitu

de, d

B

LIGO Laboratory43

Noise transients

Electronic failures Seismic noise Acoustic transients Scattered light noise Faulty radio frequency modulators Dust particles

LIGO Laboratory44

Noise transients

LIGO Laboratory45

Beam jitter filtering

Input mode cleaner filters pointing fluctuations

50 100 200 500Frequency, Hz

10-9

10-8

10-7

10-6

10-5

10-4

Ampl

itude

, 1/H

z1/2

46

Future

» What do we ultimately need?

» Medium term goals» Long term goals

47

Squeezed states of light

» reduce quantum noise» inject squeezed vacuum state through the AS port

LIGO Laboratory48

Squeezed states of light Sub-quantum noise level has been demonstrated

3.5 dB squeezing (1.5X reduced noise)

2.1 dB squeezing (1.27X reduced noise)

Typical noise without squeezing Squeezing-enhanced sensitivity

LIGO Laboratory49

Long term goals

Upgrade current facility (LIGO 3) Thermal noise can be reduced by using

cryogenic systems Quantum noise can be reduced by increasing

optical power and mirror masses Feedforward cancellation algorithms can be

applied to gravity-gradient noises

R&D for a longer facility (Lungo)

LIGO Laboratory50

Straw man sensitivity curves