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Katrin Dahl for the AEI 10 m Prototype team

AEI 10m Prototype. S uspension P latform I nterferometer for the AEI 10 m Prototype Interferometer Introductory talk. Katrin Dahl for the AEI 10 m Prototype team. September 2009 –AEI seminar. Outline. AEI 10 m Prototype Interferometer > Why is an SPI needed?

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Katrin Dahl for the AEI 10 m Prototype team

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  1. AEI 10m Prototype Suspension Platform Interferometer for the AEI 10m Prototype Interferometer Introductory talk Katrin Dahl for the AEI 10m Prototype team September 2009 –AEI seminar

  2. Outline • AEI 10m Prototype Interferometer • > Why is an SPI needed? • Relative distance measurement experiments • Experimental setup design • Test setup • Future plans

  3. The AEI 10m Prototype Goals: • Train peoplefor GEO600 • Provenewtechniques (PSL, digital controlsystem, Khalili cavity…) • Provideultralowdisplacementnoisetestingenvironment • To probe at (and later go beyond) the SQL • Entanglement of macroscopic test masses • For geodesy/LISA related experiments • ...

  4. Noise spectrum

  5. Vacuum system Tank centers separatedby11.65m Volume ca. 100 m3 22 t stainless steel Tubes: 1.5 m diameter Tanks: 3 m diameter, 3.4 m tall • 10-6mbar after about 12 hours , • 10-7mbar after about 2 weeks • ofpumping • Roughing: One 170 l/s screw pump • Main pumps: Two 2000 l/s turbo-molecularpumps • Backingand differential pumping: Two scroll pumps

  6. Seismic Attenuation System One SAS per vacuum tank, optical table goes on top of SAS Improved version of HAM-SAS Resonance frequency around 0.1Hz Up to 80dB attenuation in both vertical and horizontal directions Angstrom residual motion above 1Hz

  7. Why a Suspension Platform Interferometer? • Ease lock acquisition of cavities by reducing residual test mass motion • Reduction of burden to actuators on the mirrors • Testbed for GRACE follow-on and LISA related experiments  Sets requirements on SPI

  8. Horizontal table actuation

  9. Vertical table actuation

  10. Vertical table actuation

  11. A little bit of history LIGO-T870001-00-R

  12. Suspension Point Interferometer • monitors differential motion of the suspension points of input and end test masses LIGO-T070209-00-Z

  13. Suspension Point Interferometer LIGO-T070209-00-Z

  14. Digital Interferometry Advantages: • no specific lock point • continuous sensing • track the position of • mirrors over many µm LIGO-T080139-00-I

  15. Stabilised metrology testbed around 1m K Numata, J Camp, Proc. of SPIE Vol. 6265

  16. Stabilised metrology testbed Control bandwidth 10 Hz Yaw angle motion of 20nrad/sqrt(Hz) at 10mHz leading to about 50 times worse result for only one controlled degree of freedom K Numata, J Camp, Proc. of SPIE Vol. 6265

  17. THE AEI SPI • Requirements: • No specific lock point • Control bandwidth 100 Hz • 100pm/sqrt(Hz) and 10nrad/sqrt(Hz) @ 10mHz • Heterodyne Mach-Zehnderinterferometry • Suits our needs best • In-house knowledge ....Thanks LTP/LISA folks!

  18. Heterodyne Mach-Zehnder IFO

  19. Optical layout

  20. Measurement bench • Beam height 45mm • Overall height below 65mm

  21. Phase determination Phase isextractedfromheterodynesignalbyuse of an hardwarePhasemeterbased on FPGA chips • Preamplifierand A/D conversion • Photocurrentconvertedtovoltage • Digitisingsignals •  results in time series • Single bin discrete Fourier transform • Fourier transformatonlyonefrequency •  complexamplitudeof PD signalatfhet • Signal combinationofeach QPD quadrantleadstophase, DC, Differential WavefrontSensing (DWS) andcontrastinformation Illustration of DWS

  22. Choice of parameters • Due to the arm length mismatch (20m optical path length) a highly stabilised laser is necessary: • 280Hz/sqrt(Hz) @ 10mHz for green light (532nm) or • 140Hz/sqrt(Hz) @ 10mHz for IR light (1064nm) •  decision made for 1064nm

  23. Iodine stabilised Nd:YAG laser output power: 1W Stabilisation via Modulation Transfer Spectroscopy Michael Tröbs

  24. Choice of parameters • According to the arm length mismatch (20m optical path length) a highly stabilised laser is necessary: • 280Hz/sqrt(Hz) @ 10mHz for green light (532nm) or • 140Hz/sqrt(Hz) @ 10mHz for IR light (1064nm) •  decision made for 1064nm • Control bandwidth 100Hz  heterodyne frequency around 20kHz  new phasemeter interface needed

  25. Phasemeter Interface

  26. Choice of parameters • According to the arm length mismatch (20m optical path length) a highly stabilised laser is necessary: • 280Hz/sqrt(Hz) @ 10mHz for green light (532nm) or • 140Hz/sqrt(Hz) @ 10mHz for IR light (1064nm) •  decision made for 1064nm • Control bandwidth 100Hz  heterodyne frequency around 20kHz • Thermal driftsrequirescomponentstobemonolithicallybondedtoplatewithlow CTE (ClearCeram, CTE=0.4*10-7/K)

  27. UV curing epoxy • Advantage: almost infinite alignment time • Optocast 3553-LV-UTF • CTE = 55PPM/°C, viscosity @ 25°C = 500cps • cps = centipoise, water = 1cps, castrol oil = 1,000cps, honey = 10,000cps, ketchup = 50,000cps • Disadvantage: layer thickness is not reproducible, e.g. 10µm, 98µm, 79µm, 70µm, 37µm  misalignment in pitch •  stick to hydroxide-catalysis bonding technique

  28. Optical layout

  29. Expected transversal signals Phase difference [rad] contrast -2 -1 0 1 2 -2 -1 0 1 2 Transveral displacement of MW1 or MS1 [mm] Transveral displacement of MW1 or MS1 [mm] DC DWS [rad] Red curve: PDCW1 Black curve: PDCS1 -2 -1 0 1 2 -2 -1 0 1 2 Transveral displacement of MW1 or MS1 [mm] Transveral displacement of MW1 or MS1 [mm]

  30. Expected longitudinal signals contrast Phase difference [rad] -2 -1 0 1 2 -2 -1 0 1 2 Longitudinal displacement of MW1 or MS1 [mm] Longitudinal displacement of MW1 or MS1 [mm] DWS [rad] DC Red curve: PDCW1 Black curve: PDCS1 -2 -1 0 1 2 -2 -1 0 1 2 Longitudinal displacement of MW1 or MS1 [mm] Longitudinal displacement of MW1 or MS1 [mm]

  31. Expected rotational signals Phase difference [rad] contrast -10 -5 0 5 10 -10 -5 0 5 10 Rotation of MW1 or MS1 [mdeg] Rotation of MW1 or MS1 [mdeg] DWS [rad] DC Red curve: PDCW1 Black curve: PDCS1 -10 -5 0 5 10 -10 -5 0 5 10 Rotation of MW1 or MS1 [mdeg] Rotation of MW1 or MS1 [mdeg]

  32. Test setup • Use of vacuum • compatible • components • (free of grease)

  33. Longitudinal displacement

  34. Pitch

  35. Yaw

  36. Blind test

  37. Blind test

  38. Next steps • Stabilisation loops • Amplitude stabilisation @ 20kHz • Optical pathlenght difference stabilisation • Bond optics • Build calibrated QPD • Use CDS via phasemeter interface • Install final setup inside vacuum envelope • Calibrate signals • Table actuation • Reach design sensitivity

  39. The End

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