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Alignment Control of GEO 600

Alignment Control of GEO 600. Hartmut Grote for the GEO600 team Institut für Atom- und Molekülphysik University of Hannover Max-Planck-Institut für Gravitationsphysik 9. July 2003. Autoalignment: Why ?. Superimpose beam axes Maximize light power Stabilze optical gain

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Alignment Control of GEO 600

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  1. Alignment Control of GEO 600 Hartmut Grote for the GEO600 team Institut für Atom- und Molekülphysik University of Hannover Max-Planck-Institut für Gravitationsphysik 9. July 2003

  2. Autoalignment: Why ? • Superimpose beam axes • Maximize light power • Stabilze optical gain • Center beam spots on mirrors • Minimize angular to longitudinal noise coupling

  3. Autoalignment: How ? • Differrential wavefront sensing (analog feedback for 14 DOF in GEO) • Spot position sensing (digital feedback for 20 DOF in GEO)

  4. Modecleaner Autoalignment Bandwidth: 1kHz

  5. Modecleaner Reflected Power Pitch DWS feedback ... and yaw DWS feedback Reflected power [Arb.] Time [s]

  6. PR und MI Autoalignment

  7. Double – Triple Pendulum Blades Stack Magnet-Coil Actuator Range: 100 µm, Typ. DC-10Hz Intermediate mass Mirror Elektrostatic Actuator Range: 1 µm (DC), Typ. 10-100Hz 3mm

  8. Electrostatic Drive Processing square root with analog electronics Peak force: 30 µN Needed for acquisition Maximal mirror speed with PR gain 300 is 100 nm/s

  9. Intermediate Mass Actuator Alignment transfer function Amplitude [Abs.] Frequency [Hz]

  10. Michelson Power Levels Dark port Light power [Arb.] Time [s] Light power [Arb.] PR cavity Time [s]

  11. Spectral Density of MI-DWS Feedback Differential MCe/MCn alignmrnt [rad/sqrt(Hz)] Error signal Frequency [Hz]

  12. DWS Feedback Noise • Noise coupling by spot position deviations Induced length noise RMS deviation from center of pitch / yaw RMS angular noise Angular noise in GW band (e.g. caused by DWS feedback)

  13. Michelson Strain Sensitivity S1 Sqrt-noise HV-amplifier noise Strain sensitivity [1/sqrt(Hz)] Noise limit Michelson DWS feedback noise (1mm) Frequency [Hz]

  14. PR and MI Autoalignment Matrix diagonalization for 4 dimensions

  15. Computer Control

  16. Operation during S1 • 98% duty cycle, almost no human interaction required BS pitch FB [µrad] Time [days] Temp. [Deg. C] Time [days] Time

  17. Summary and Outlook • Autoalignment for modecleaners and power recycled Michelson complete (14 DOF DWS, 20 DOF spot pos.) • Long term stable operation achieved (~98% duty cycle during S1, longest lock >121 hours) • Michelson DWS feedback needs 10-20dB more gain at 0.5-2 Hz (reach 10nradRMS for MI arms) • Signal recycling DWS feedback in near future

  18. Differential Wavefront Sensing Detect angle between wavefronts in “near-“ and “far“ field • Sensitivity typically 10 p rad / sqrt(Hz)

  19. Modelliertes Alignment am PR MI

  20. A larger mismatch in the radii of curvature makes the system more sensitive to misalignment. Michelson Error Signal

  21. Autoalignment Experimental setup for 1 cavity

  22. Autoalignment Experimental setup for 1 cavity Differential wavefront sensing Orthogonalization < 1/10 Bandwith 0.2 or 6 Hz

  23. Autoalignment Experimental setup for 1 cavity Local beam centering servos Bandwidth ~ 1kHz

  24. Autoalignment Experimental setup for 1 cavity Spot position control

  25. Autoalignment setup PR + MI cavity

  26. Misalignment eines Resonators Achse der Eigenmode Achse des eintretenden Strahls Messe Winkel zwischen Wellenfronten an zwei verschiedenen Positionen

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