Current Progress of Development of Laser Interferometry for LISA-type Mission in China

1. Gravitational Waves: New Frontier 16-18 January, 2013 Research Park, Seoul National University, KOREA Current Progress of Development of Laser Interferometry for LISA-type Mission in China Hsien-Chi Yeh School of Physics Huazhong University of Science & Technology

2. Outline 1 Motivation and Strategy 2 Scheme and Error Budget 3 Current Progress at HUST 4 Roadmap and Conclusion

3. Motivation: Gravitational Waves Detection in Space • Orbit precession in the perihelion of planets • Deflection of light by solar gravity • Redshift of spectral lines • Frame dragging • Gravitational waves

4. Direct Measurement of Gravitational Waves LIGO Hanford Observatory LISA Space Antenna Baseline: 5106 km Strain sensitivity: ~10-22/Hz1/2 Sensing frequency: 10-4 ~ 0.1Hz Baseline: 4 km Strain sensitivity: ~10-22/Hz1/2 Sensing frequency: 40 ~ 10kHz

5. eLISA/NGO & LISA Pathfinder • Arm length: ~106km • Duration: 2 years (total 4 years) • Interferometry: 18pm/Hz1/2 • Residual acceleration (Drag-Free): 310-15 m/s2/Hz1/2

6. Sensitivity Requirements of GWD Missions 10-18 10-19 10-20 10-21 10-22 10-23 10-24 10-25 ASTROD (2A.U.) LIGO A-LISA (ALIA) (LISA type, 5105km) KAGRA 10-5 10-4 10-3 10-2 10-1 100 101 102 103

7. Strategy: Treat SAGM as LISA Pathfinder Space Advanced Gravity Measurements (SAGM) GRACE-like mission • Satellite-to-satellite tracking: • Separation: 50~200 km • Altitude: 250~400 km • Drag-free control: 10-11 m/s2/Hz1/2@0.1Hz • Measurement: • Laser ranging (range: 30~50 nm, range-rate: < 100 nm/s) • GPS (~1 mm)

8. Schematics of Inter-Satellite Laser Ranging 200km Environment Control Environment Control Inertial Sensor Inertial Sensor Drag Free Control Drag Free Control Beam Collimation & Pointing Control Beam Collimation & Pointing Control Transponder With Phase- Locked Loop Heterodyne Laser Interferometer Proof Mass Proof Mass Inertial Sensor Inertial Sensor Satellite Platform Satellite Platform

9. Error Budget of Laser Ranging

10. 10-m Prototype of Laser Ranging System Installed at HUST (2009~2010) 5-nm step Driving by PZT stage

11. FPGA-Based Digital Phasemeter (2010~2011) LP Filter PI Input Anti-A Filter ADC Numerical Control Oscillator Disp. Speed Freq./Phase outputs Down sampling 50MHz clock Noise level: ~10-5 rad/Hz1/2@0.1Hz

12. amplitude: 25 pm Ultra-Stable Optical Bench (2011-2012) Cooperation with AEI, Hannover

13. Master laser Slave laser Transponder-Type Laser Ranging (2012) Homodyne OPLL Displacement output Phase Locked Control Phase Meter Weak-light: 100 nW Proof Mass Proof Mass Optical Bench Optical Bench PZT 1-nm sinusoidal motion

14. Laser Frequency Stabilization F-P cavity for frequency stabilization PDH scheme NASA HUST NPL NIST

15. Beam Pointing Angle Measurement • Contrast Measurement • Divergence angle：10-4 rad • Received power：10-8 W • Contrast  misalignment angle • precision：10-5 rad • Phase-difference Measurement • Divergence angle：3.510-5 rad • Received power：10-7 W • Phase difference  misalignment angle • precision：10-7 rad

16. Proof Mass & Capacitive Sensor • 6-DOF • Sensitivity: 10-6 pF/Hz1/2 • FPGA-based electronics

17. Multi-Stage Pendulum for Performance Test

18. Preliminary Test Result of Accelerometer Torsion-pendulum-based testing system Noise level: ~10-10 m/s2/Hz1/2@0.1Hz

19. Proposed Timeline • Inter-Satellite Laser Interferometer • For Gravitational Waves Detection • Inter-satellite distance: 105~106 km • Sensitivity: < 1 pm/Hz1/2 • Transponder-type heterodyne interferometry • Drag-free control: 10-14 m/s2/Hz1/2@0.1Hz • Special methods to decompress laser frequency noise • Pointing control: 10-9 rad/Hz1/2 • Inter-Satellite Laser Ranging • For Earth’s Gravity Recovery • Inter-satellite distance: 50-200 km • Sensitivity: 30-50 nm/Hz1/2 • Transponder-type heterodyne interferometry • Drag-free control: 10-11 m/s2/Hz1/2@0.1Hz • Pointing control: 10-6 rad/Hz1/2 2020 2025 2010 2015 2030

20. Conclusions • GW detection (long-term goal) • Earths gravity recovery (short-term goal): • SAGM as our LISA Pathfinder • Preliminary demonstration: • (1) nanometre-level transponding laser ranging with 100-nW weak-light phase locking • (2) 6-DOF electrostatic inertial sensor • 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 • (4) ultra-precision inertial sensor and proof mass

21. Center for Gravitational Experiments Professor: 12, Associate Professor: 3 Lecturer: 4, Post-Doctor: 5 Graduate students: ~ 60 • Lab. Area:：~ 7000 m2 • Building: 2800 m2 • Cave lab.: 4000 m2 • Machining shop: 600 m2 Temp. variation Seismic vibration

22. Center for Gravitational Experiments • Measurement of G constant • Test of Newtonian inverse-squared law (torsion balance & AFM) • Test of Equivalence Principle • Laser interferometry for GW detection Gravitational Physics CGE • Cold-atom physics • Optical frequency standard & laser frequency stabilization • Quantum-optic experiments AMO • Atom-interferometry-based standard of g • Superconducting accelerometer • Electrostatic accelerometer • Calibration of weak force Measurement of Gravity

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