Current progress of developing Inter-satellite laser interferometry for Space Advanced Gravity Measurements Hsien-Chi Yeh School of Physics Huazhong University.

Current progress of developing Inter-satellite laser interferometry for

Space Advanced Gravity Measurements

Hsien-Chi Yeh

School of PhysicsHuazhong University of Science & Technology

22 May, 2012

Outline

11 Motivation and Strategy

22

Current Progress at HUST33

Scheme and Error Budget

Roadmap and Conclusion44

Orbit precession in the perihelion o

f planets Deflection of light by solar gravity Redshift of spectral lines Frame dragging

Gravitational waves

Motivation: Gravitational Waves Detection in

Space

Frequencyrange (Hz)

Arm lengthDisplacement

noise (pm/Hz1/2)Acceleration noise

(ms-2/Hz1/2)

LISA 10-4 ~ 10-1 5109 m 20 310-15 @1mHz

ALIA 10-3 ~ 1 ~ 5108 m ~ 0.1 ~ 310-16 @10mHz

ASTROD 10-6 ~ 10-3 ~ 31011 m ~ 2000 ~ 810-16 @0.1mHz

10-18

10-19

10-20

10-21

10-22

10-23

10-24

10-25

LIGO

A-LISA (ALIA)(LISA type, 5105km)

ASTROD(2A.U.)

10-5 10-4 10-3 10-2 10-1 100 101 102 103

Sensitivity Requirements of GWD Missions

Strategy: Treat SAGM as LISA Pathfinder

Satellite-to-satellite tracking (SST):• Separation: ~100 km• Altitude: 250~300 km (declined orbit)• Measurement:

Laser interferometer (30~50 nm)GPS (1mm)

GRACE-like mission

Space Advanced Gravity Measurements (SAGM)

Transponder-Type Laser Ranging System

200km

BeamCollimation & Pointing

Control

ProofMass

Inertial Sensor

Inertial Sensor

HeterodyneLaser

Interferometer

Satellite Platform

EnvironmentControl

Dra

g F

ree

Con

trol Beam

Collimation & Pointing

Control

ProofMass

Inertial Sensor

Inertial Sensor

TransponderWith Phase-Locked Loop

Satellite Platform

EnvironmentControl

Dra

g F

ree

Con

trol

OPLL

MD

M cLt

cL

2)(

2

Error Source Error component

Pre-stabilized laser: f < 50 Hz/Hz1/2

L = 200 km 30.0 nm/Hz1/2

Thermal drift of O.B. (fused quartz):thermal variation: 0.01Kunbalanced OPL: 1 cm

2.0 nm/Hz1/2

Divergence angle of laser beam:div ~ 3.510-5 rad

Pointing control:dc ~ 10-5 rad, jit ~ 10-5 rad/Hz1/2

9.0 nm/Hz1/2

Phasemeter resolution 1.0 nm/Hz1/2

Residual error of OPLL 3.0 nm/Hz1/2

Shot noise and Ionosphere effect < 0.1 nm

(RSS) Total ~ 35 nm/Hz1/2

Error Budget

10-m Prototype of Laser Ranging SystemInstalled at HUST (2009~2010)

5-nm stepDriving by PZT stage

10-4

10-3

10-2

10-1

100

101

10-8

10-6

10-4

10-2

100

102

Ph

ase L

AS

D [

rad

*Hz

-1/2]

Frequency [Hz]

Noise in digital systemTwo 9.999MHz inputNoise level of GRACENoise level of LISA

FPGA-Based Digital Phasemeter (2010~2011)

1200 1220 1240 1260 1280 1300

-3.21

-3.208

-3.206

-3.204

-3.202

-3.2

-3.198

-3.196

-3.194

Time origin: 2011-06-15 17:30:00.000

Ph

ase

[deg

]

Time [s]

1.txt_01

Phase (peak-to-peak) = 0.01o 30pm

210-5 rad/Hz1/[email protected]

Ultra-Stable Optical Bench (2011-2012)

Cooperation with AEI, Hannover

0 0.2 0.4 0.6 0.8 1-60

-40

-20

0

20

40

60

80Time origin: 2012-04-10 04:00:00.000

Dis

pla

cem

en

t [p

m]

Time [s]

PZT-4mVpp-step data after fitted polynomial taken out

Above data after smoothing with 4-point averageamplitude: 25 pm

Transponder-Type Laser Ranging (2012)

ProofMass

OpticalBench

ProofMass

OpticalBench

PhaseMeter

PhaseLockedControl

Maste

r la

ser

Sla

ve

lase

r

Displacement output

PZT

1-nm sinusoidal motion

1784 1785 1786 1787 1788 1789 17903.7646

3.7647

3.7648

3.7649

3.765

3.7651

3.7652x 10

4 Time origin: 2011-12-31 20:40:00.000

Dis

pla

cem

en

t [

nm

]

Time [s]

Displacement data with 1nm amplitude 1Hz sinewaveDisplacement data after filtered

Weak-light: 10 nW

Homodyne OPLL

Key factors：• Mechanical stability of cavity• Thermal stability of cavity• Environment control• Mode matching

F-P cavity forLaser frequency stabilization

Laser Frequency Stabilization

Beam Pointing Angle Measurement

Phase-difference Measurement• Divergence angle： 3.510-5 ra

d• Received power： 10-7 W• Phase difference misalignme

nt angle• precision： 10-7rad• Jitter： 10-6rad/Hz1/2

Contrast Measurement• Divergence angle： 10-4 rad• Received power： 10-8 W• Contrast misalignment angle• precision： 10-5 rad

2/)( BA

BA

II

IIcontrast

2010 20202015 2025 2030

Inter-Satellite Laser RangingFor Earth’s Gravity Recovery

• Inter-satellite distance: 50-200 km

• Sensitivity: 30-50 nm/Hz1/2

• Transponder-type heterodyne interferometry

• Pointing control: 10-6 rad/Hz1/2

Inter-Satellite Laser Interferometer

For Gravitational Waves Detection

• Inter-satellite distance: 105~106 km

• Sensitivity: < 1 pm/Hz1/2

• Transponder-type heterodyne interferometry

• Special methods to decompress laser frequency noise

• Pointing control: 10-9 rad/Hz1/2

Proposed Timeline

• GW detection (long-term goal)Earths gravity recovery (short-term goal):SAGM as our LISA Pathfinder

• Preliminary demonstration:transponder-type laser ranging with weak-light phase locking

• Focused tasks in the next step: (1) space-qualified frequency-stabilized laser(2) laser beam pointing measurement and control(3) simulation experiment of plasma in ionosphere

Conclusions

Thank youfor your attentions!