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The Mesa Beam Update

The Mesa Beam Update.

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The Mesa Beam Update

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  1. The Mesa BeamUpdate Juri Agresti1, Erika D’Ambrosio1, Riccardo DeSalvo1, Danièle Forest2, Patrick Ganau2, Bernard Lagrange2, Jean-Marie Mackowski2, Christophe Michel2,John Miller1,3,Jean-Luc Montorio2, Nazario Morgado2, Laurent Pinard2, Alban Remillieux2,Barbara Simoni1, Marco Tarallo1, Phil Willems1 1. Caltech/ LIGO 2. LMA Lyon/ EGO 3. University of Glasgow

  2. Overview • Introduction • Results • HOM • Fundamental mode • Tilt sensitivty LIGO R&D

  3. Introduction • Detectors limited by fundamental thermal noise • Spectral density scales as 1/wn (different n for each type of noise) • Diffraction prevent dramatically increasing beam size LIGO R&D

  4. Gaussian beams sample a small portion of mirror’s surface Introduction Sensed Avg LIGO R&D

  5. Optimisation produces the mesa beam Mesa Beam Higher peak power Steep rim Slow exponential fall Aspheric profile Steeper fall LIGO R&D

  6. 7.32 m folded cavity Rigid structure Suspended in custom vacuum tank Cavity Flat folding mirror Flat input mirror MH mirror 2x 3.5 m INVAR rod Vacuum pipe LIGO R&D

  7. We have been able to lock to higher order modes These modes exhibit good agreement with theory Results TEM10 LIGO R&D

  8. Results - HOM Diffraction around beam baffle eliminated LIGO R&D

  9. Modes resemble HG and LG sets LG10 fit MH10 fit Gaussian? LIGO R&D

  10. Alignment is taxing Long periods were spent aligning input optics and cavity mirrors The Fundamental? 4mrad tilt LIGO R&D

  11. The reference during alignment was changed from the intensity profile to the transverse mode spectrum Improving Alignment LIGO R&D

  12. The First Mesa Beam LIGO R&D

  13. Non-Linear Fit X LIGO R&D

  14. Non-Linear Fit Y LIGO R&D

  15. How Was This Achieved? • We have reinforced flexible mirrors with aluminium rings • Thicker substrates have been ordered LIGO R&D

  16. How Was This Achieved? • Improved atmospheric isolation • Better stability ‘in lock’ LIGO R&D

  17. More power in the fundamental mode Improved spectrum How Was This Achieved? LIGO R&D

  18. Alignment LIGO R&D

  19. Rsq = 0.996 Rsq = 0.992 Best Mesa Beam LIGO R&D

  20. Best Mesa Beam Jagged top due to imperfect mirrors LIGO R&D

  21. Tilts of Spherical Mirrors • Tilts of spherical mirrors translate optical axis LIGO R&D

  22. Tilt Sensitvity • Controllability of beam is key • Decided to first investigate tilt sensitivity • Tilt MH mirror about a known axis LIGO R&D

  23. 2 mrad simulated 3.85 mrad experiment 2.57 mrad experiment Profiles • Profiles along tilt axis LIGO R&D

  24. Excuses • Lack of temporal stability • vacuum? • Stiction • PZTs are bad LIGO R&D

  25. Summary • We are able to produce acceptable flat-topped beams with imperfect optics • We have begun to make a quantitative analysis of mesa beam • Beam size appears correct • Tilt sensitivity shows correct trends LIGO R&D

  26. Further Work With This Set Up • Improve profile using new flat mirrors • Repeatability/ stability – vacuum operations • Complete tilt sensitivity measurements • Test other two MH mirrors – mirror figure error tolerances • Long term – design and build half of a nearly concentric MH Cavity LIGO R&D

  27. Riccardo DeSalvo Phil Willems Mike Smith GariLynn Billingsley Marco Tarallo Juri Agresti Chiara Vanni Grazie LIGO R&D

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