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

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

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

Direct Measurement of Gravitational Waves LIGO Hanford Observatory Baseline: 4 km Strain sensitivity: ~ /Hz 1/2 Sensing frequency: 40 ~ 10kHz Baseline: 5  10 6 km Strain sensitivity: ~ /Hz 1/2 Sensing frequency: ~ 0.1Hz LISA Space Antenna

eLISA/NGO & LISA Pathfinder Arm length: ~10 6 km Duration: 2 years (total 4 years) Interferometry: 18pm/Hz 1/2 Residual acceleration (Drag- Free): 3  m/s 2 /Hz 1/2

Frequency range (Hz) Arm length Displacement noise (pm/Hz 1/2 ) Acceleration noise (ms -2 /Hz 1/2 ) LISA10 -4 ~  10 9 m ~ 20 3  10 ALIA10 -3 ~ 1 ~ 5  10 8 m ~ 0.1 ~ 5  10 ASTROD10 -6 ~ ~ 3  m ~ 2000 ~ 8  LIGO A-LISA (ALIA) (LISA type, 5  10 5 km) ASTROD (2A.U.) Sensitivity Requirements of GWD Missions KAGRA

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

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

Error SourceError component Pre-stabilized laser:  f < 50 Hz/Hz 1/2 L = 200 km 30.0 nm/Hz 1/2 Thermal drift of O.B. (fused quartz): thermal variation: 0.01K unbalanced OPL: 1 cm 4.0 nm/Hz 1/2 Divergence angle of laser beam:  div ~ 3.5  rad Pointing control:  dc ~ rad,  jit ~ rad/Hz 1/2 9.0 nm/Hz 1/2 Phasemeter resolution 1.0 nm/Hz 1/2 Residual error of OPLL 3.0 nm/Hz 1/2 Coupling error between OB and PM 5.0 nm/Hz 1/2 Shot noise and Ionosphere effect < 0.1 nm (RSS) Total~ 32 nm/Hz 1/2 Error Budget of Laser Ranging

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

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

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

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

F-P cavity for frequency stabilization Laser Frequency Stabilization NISTNPL NASA PDH scheme HUST

Beam Pointing Angle Measurement Phase-difference Measurement Divergence angle ： 3.5  rad Received power ： W Phase difference  misalignment angle precision ： rad Contrast Measurement Divergence angle ： rad Received power ： W Contrast  misalignment angle precision ： rad

Proof Mass & Capacitive Sensor 6-DOF Sensitivity: pF/Hz 1/2 FPGA-based electronics

Multi-Stage Pendulum for Performance Test

Preliminary Test Result of Accelerometer Noise level: ~ m/s 2 /Hz Torsion-pendulum-based testing system

Inter-Satellite Laser Ranging For Earth’s Gravity Recovery Inter-satellite distance: km Sensitivity: nm/Hz 1/2 Transponder-type heterodyne interferometry Drag-free control: m/s 2 /Hz Pointing control: rad/Hz 1/2 Inter-Satellite Laser Interferometer For Gravitational Waves Detection Inter-satellite distance: 10 5 ~10 6 km Sensitivity: < 1 pm/Hz 1/2 Transponder-type heterodyne interferometry Drag-free control: m/s 2 /Hz Special methods to decompress laser frequency noise Pointing control: rad/Hz 1/2 Proposed Timeline

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 Conclusions

Center for Gravitational Experiments Lab. Area: ： ~ 7000 m 2 Building: 2800 m 2 Cave lab.: 4000 m 2 Machining shop: 600 m 2 Seismic vibration Temp. variation Professor: 12,Associate Professor: 3 Lecturer: 4,Post-Doctor: 5 Graduate students: ~ 60

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

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