LISA Technology: A Status Report

Transcription

1 LISA Technology: A Status Report Guido Mueller University of Florida Minnesota

2 Content LISA Concept Gravitational Reference Sensor Interferometry Measurement System Status/Outlook 2

3 LISA Concept 3 spacecraft constellation S/C separated by 5x10 6 km Two Drag-free proof masses inside each S/C Interferometer measure variations in proof mass distances Earth-trailing solar orbit 3

4 LISA Requirements GW-Strain: h = δl L Red: Requirement Blue: Goal Limited by noise in the IMS (Interferometry Measurement System): S 1/2 pm δl (f) 18 Hz 1+ 2mHz f 2 Limited by noise (residual acceleration) in the DRS (Disturbance Reduction System): S 1/2 m δα (f) s 2 Hz mhz f 4

5 Disturbance Reduction System Shield the Proof masses from all external forces SUN Solar Pressure Build a S/C around it Drag free navigation Monitor S/C to PM position PM Steer the S/C around the PM µn-thrusters 5

6 Experimental Verification of DRS Torsion pendulum in Trento Space-based test with LISA Pathfinder Other experiments with Gravitional Reference Sensors: Space: Grace, Goce, Microscope,... Torsion Pendula: Adelberger, Gundlach,... 6

7 Experimental Verification of DRS Capacitive Sensing: δx(f) =2 nm Hz δθ(f) = 200 nrad Hz 6cm The Noise model: a n = f str m + k m Spring-like Actuation: x n + f S/C Mω 2 k = C X d 2 V 2 inj 7

8 Experimental Verification of DRS The Noise model: a n = f str m + k m x n + f S/C Mω 2 Stray Forces: - Gravitation - Electro-magnetic - Radiation pressure - Residual gas

9 Status of LTP All flight hardware has been delivered except FEEPs (µn-thrusters) Final Caging Mechanism Engineering model of Caging mechanism has been tested All subsystems are now being integrated into engineering model Flight unit is under construction S/C+Payload is just passed Transfer orbit thermal balance tests (see pic) Next tests: Environmental and vibrational tests mid 2011 To be launched 2012/13 9

10 LISA Requirements GW-Strain: h = δl L Red: Requirement Blue: Goal Limited by noise in the IMS (Interferometry Measurement System): S 1/2 pm δl (f) 18 Hz 1+ 2mHz f 2 Limited by noise (residual acceleration) in the DRS (Disturbance Reduction System): S 1/2 m δα (f) s 2 Hz mhz f 10

11 IMS IMS Environment: Orbits cause relative Motion of Proof Masses: v = ±10 m s Changing Doppler shifts Point ahead angle L 12 PM 1 L 13 Changes angles: Maintain Alignment φ ±0.5 PM 2 L 23 PM 3 Very dynamic Interferometer 11

12 Interferometry Measurement System: Spreads over entire configuration 5 Gm 5 Gm 5 Gm 12

13 Spacecraft Laser Bench Optical Benches Telescopes Proof Mass Photo detector Laser System Phase Modulator 13

14 Spacecraft Laser Bench Optical Benches Telescopes Proof Laser Mass System IMS-Signals: Phase Evolution of Laser Beat Signals Dominated by laser frequency noise Photo detector Phase Modulator 13

15 Time Delay Interferometry sin (ω 1 t + φ 1 (t)) L1 S 12 = φ 1 (t) φ 2 (t τ 21 )+δl 21 (t) sin (ω 2 t + φ 2 (t)) L2 PM1 S 13 = φ 1 (t) φ 3 (t τ 31 )+δl 31 (t) PM2 S 21 = φ 1 (t τ 12 ) φ 2 (t) δl 12 (t) S 31 = φ 1 (t τ 13 ) φ 3 (t) δl 13 (t) PM3 L3 Snm (t τ j )= δl nm (t τ j ) sin (ω 3 t + φ 3 (t)) 14

16 Time Delay Interferometry sin (ω 1 t + φ 1 (t)) L1 S 12 = φ 1 (t) φ 2 (t τ 21 )+δl 21 (t) sin (ω 2 t + φ 2 (t)) L2 PM1 S 13 = φ 1 (t) φ 3 (t τ 31 )+δl 31 (t) PM2 S 21 = φ 1 (t τ 12 ) φ 2 (t) δl 12 (t) S 31 = φ 1 (t τ 13 ) φ 3 (t) δl 13 (t) PM3 Cancels laser frequency noise, keeps signal L3 Snm (t τ j )= δl nm (t τ j ) sin (ω 3 t + φ 3 (t)) 14

17 Digital The Tool: Phasemeter Phase Lock Loop PD sin (Ω B t + φ) ADC USO Local τ DDS sin CIC 128 Clock f 128 P-I DSP φ 2 17 Ω O 15

18 Phasemeter Requirements: Phase Noise δφ(f) < 2π λ 1pm 6 rad 2π 10 Hz Hz Diff. Clock Noise: δt(f) < δφ(f) Ω B < 0.05 ps Hz Residual noise due to laser frequency noise: δφ =2πδν τ Timing (Ranging): τ =3ns L =1m Laser Frequency Noise: δν(f) < 141 Hz Hz mhz f 4 16

19 Phasemeter Status Digital Part: Filters Digital Noise Meet requirements cylc/rthz Frequency [Hz] ADCs: Timing Jitter Dispersion Might need Pilot tone Temperature stabilization 17

20 Laser Frequency Noise δν(f) < 141 Hz Hz mhz f 4 New Requirement Options: Stabilized to Zerodur Reference Cavity using PDH Heterodyne Interferometry use LISA Phasemeter Cavity Mach-Zehnder (LTP-style) Arm Locking 18

21 Laser Frequency Noise With Arm Locking δν(f) < 141 Hz Hz mhz f 4 New Requirement Options: Stabilized to Zerodur Reference Cavity using PDH Heterodyne Interferometry use LISA Phasemeter Cavity Mach-Zehnder (LTP-style) Arm Locking 19

22 Ranging PRN Ranging: Modulate/Demodulate Carrier/Carrier Beat Phase with PRN Known local start times used to synchronize clocks m Measures also S/C velocities Differential Clock rates Inter S/C Communication: Switch Sign of PRN Code 20

23 Clock Noise Fiber Modulator Local Laser 2-8 GHz Up 10MHz USO Sidebands carry clock noise SB/SB beat 1MHz off from Carrier/Carrier beat SB/SB phase - Carrier/Carrier beat gives clock noise 14

24 Clock Noise Phase Fidelity of Fiber Modulator: Requirement relaxed by 20 MHz f Mod ~ RL UP UP X EOM L1 EOM X ~ CC SS 3 PM cylc/rthz Frequency [Hz] 22 Successfully tested at AEI, JPL, UF integrated at JPL and UF into testbeds Additional signals for TDI combinations 15

25 TDI for LISA LISA uses 18+ Signals: to cancel: Laser frequency noise Spacecraft motion to generate: TDI Combinations Depend only on PM motion 3 Types of IFO: 1. Bench to Bench Measure S/C to S/C motion 2. Backlink Correlate the local laser 3. Proof mass to Bench Measure PM to S/C motion 23

26 JPL Testbed Injected 800Hz/rtHz laser frequency noise 6 GHz clock noise transfer PRN Ranging Two independent multi-channel PM Two independent clocks (USOs) Post-processed TDI: Fractional delay filtered Time delays determined by PRN Clock Noise corrected 10 9 suppressen at 3mHz See: Experimental Demonstration of Time-Delay Interferometry for the Laser Interferometer Space Antenna, Glenn de Vine, Brent Ware, Kirk McKenzie, Robert E. Spero, William M. Klipstein, and Daniel A. Shaddock, Phys. Rev. Lett. 104, (May 2010) 24

27 UF Testbed Generation of TDI-X Combination with: One Laser per S/C LISA-like delays Doppler shifts GW Cycl./rtHz Frequency [Hz] Optical PLL s Frequency pre-stabilization Fractional Delay Filtering Ranging with ranging tone at 1.5Hz Within factor 4 of LISA req. Limited by ADC noise Use Common Clock 25

28 TDI for LISA LISA uses 18+ Signals: to cancel: Laser frequency noise Spacecraft motion to generate: TDI Combinations Depend only on PM motion 3 Types of IFO: 1. Bench to Bench Measure S/C to S/C motion 2. Backlink Correlate the local laser 3. Proof mass to Bench Measure PM to S/C motion 26

29 Local Reference Beat Ref Phase Meter Ref Compares local lasers: Laser counter-propagate through fiber One Beat Signal on each bench Requires reciprocity of fiber Fiber: Reciprocity of optical path? From Laser Bench Courtesy of the Albert Einstein Institute in Hannover 27

30 Local Interferometer Phase Meter S a = φ 1 (t) φ 2 (t)+ω 1 δl 1a ω 2 δl 2a S b = φ 1 (t) φ 2 (t)+ω 1 δl 1b ω 2 δl 2b To/From Other Bench Ref L 1a Phase Meter δl < 1 pm Hz 3 nm Hz on Bench δl 2b L 1b L 2a L 2b PM S a S b : measures changes in Bench to Proof mass distance From Pol. Laser Bench Wave plate Vacuum window 28

31 TDI for LISA LISA uses 18+ Signals: to cancel: Laser frequency noise Spacecraft motion 3 Types of IFO: 1. Bench to Bench Measure S/C to S/C motion 2. Backlink Correlate the local laser to generate: TDI Combinations Depend only on PM motion Length measurements are under control 3. Proof mass to Bench Measure PM to S/C motion 29

32 Half of the story... Critical Components: Lasers Switch board Telescopes Photo detectors Point Ahead Actuator... 30

33 Laser Concept Fiber Modulator Master Laser Fiber Amplifier 10-50mW 1-2W Laser: >1W Around 1064nm Single Frequency Single Mode Challenges: Shot noise limited 2MHz Phase fidelity of Ampl. Space qualified (Radiation,...) Lifetime 31

34 Laser Development Master laser: Tesat laser (LTP) Fiber laser ECDL Thermal cycl. of Fiber Laser Pictures: Courtesy of Kenji Numata, GSFC Phase Fidelity of Laser Amplifier: Initial test results Pictures: Courtesy of Gerhard Heinzel, AEI 32

35 Telescope 40cm Diameter 60cm Long 50nm Wavefront error 2 Concepts: On-axis Cassegrain pm/rthz stability um long term stability Scattered light from Secondary Schiefspiegler Off-axis, no direct scattered light Optical truss IFO Refocus mechanism Telescope requirements similar to Herschel and Silex telescopes 33

36 Half of the story... Critical Components: Lasers Telescopes Point Ahead Actuator Prototype has been successfully tested Photo detectors Experiments started at GSFC and AEI... Still many optical, mechanical, electrical components need to be tested, but So far, so good 34

37 The End 35