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Thermal Compensation in LIGO

Thermal Compensation in LIGO. Rupal S. Amin. LIGO Layout Thermal Aberrations Thermal Issues Compensation Systems Model Closing Remarks. Outline. ETMy. P ower R ecycled M ichelson. Fabry-Perot Cavity. ITMy. Carrier Resonant Sideband pair Non-resonant sideband pair. RM. ITMx.

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Thermal Compensation in LIGO

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  1. Thermal Compensation in LIGO Rupal S. Amin LIGO-G0900358.Rupal S. AminGCGW 17 April 2009

  2. LIGO Layout • Thermal Aberrations • Thermal Issues • Compensation Systems • Model • Closing Remarks Outline LIGO-G0900358.Rupal S. AminGCGW 17 April 2009

  3. ETMy Power Recycled Michelson Fabry-Perot Cavity ITMy Carrier Resonant Sideband pair Non-resonant sideband pair RM ITMx ETMx BS Optical Layout LIGO-G0900358.Rupal S. AminGCGW 17 April 2009

  4. Causes • HEAT GRADIENT • Thermal Lensing • Thermal Expansion • Induced Birefringence • … • Effects • Differential Expansion Cold  Hot  Aberrations Main Laser Beam Thermal Aberrations LIGO-G0900358. Rupal S. Amin GCGW 17 April 2009

  5. PRM Stability Issues • Not stable for RSB • Cavity g-factor > 1 • No containment in cold state • Contrast Defect • Imbalanced thermal lenses increases junk light output Thermal Issues: eLIGO LIGO-G0900358.Rupal S. AminGCGW 17 April 2009

  6. Towards 4 km arm Initial Test Mass Pointing optics CO2 laser light TCS Laser Box Thermal Compensation System LIGO-G0900358.Rupal S. AminGCGW 17 April 2009

  7. TCS Hardware LIGO-G0900358.Rupal S. AminGCGW 17 April 2009

  8. Need a thermal model of the INTERFEROMETER (Dramatic music) Solution for eLIGO LIGO-G0900358.Rupal S. AminGCGW 17 April 2009

  9. 1)Comsol FEM of ITMs 0) Matlab 1 2 Interferograms, t(f) results, Power build up, Beam parameters 2) Matlab 3 FINESSE 4 Model: Matlab+Comsol+Finesse LIGO-G0900358.Rupal S. AminGCGW 17 April 2009

  10. Comsol Finite Element Analysis • Simulate mirror heating patterns with and without TCS Inputs: Boundary Conditions Substrate Materials Outputs: Deformed Surface Thermally Dependent n Step 1: FEM of ITMs LIGO-G0900358.Rupal S. AminGCGW 17 April 2009

  11. Optical interaction only • No mechanical interactions • No radiation pressure Finesse: http://www.rzg.mpg.de/~adf/ Luxor: http://www.aei.mpg.de/~jah/luxor.html Luxor GUI config builder Config file With layout and simple instructions Step 2: In-house sim. code LIGO-G0900358.Rupal S. AminGCGW 17 April 2009

  12. LHO AS patterns Mich only Jan 15, 2009 Simulated Interferogram K. Dooley ilog LHO Step 3: FEM + Simulation LIGO-G0900358.Rupal S. AminGCGW 17 April 2009

  13. Interferometers require thermal compensation to maintain stability at high power • Thermal model construction in progress • Sensible control signals are needed • Cannot assume that new TCS behave exactly like old TCS Closing LIGO-G0900358.Rupal S. AminGCGW 17 April 2009

  14. Special Thanks to • J. Giaime LSU Associate Prof. of Physics • Phil WillemsTCS Group Leader CIT • Aidan Brooks • Cheryl Vorvick • Carl Adams • ViginioSannibale • MohanaMageswaran • NSF grant number: • NSF-PHY-0605496 Thanks to… LIGO-G0900358.Rupal S. AminGCGW 17 April 2009

  15. Unexpected TCS induced ASC signals • Due to surface expansion and mirror expansion OSEMs Cold lzr Heated w/ TCS Optical lever response Magnets lzr ~10 mrad Half-story OSEM response Problems with cut and paste LIGO-G0900358.Rupal S. AminGCGW 17 April 2009

  16. Common Differential Sideband power build-up iLIGO AS_I In-phase demodulation eLIGO Sideband power build-up? Working on it Problems with cut and paste LIGO-G0900358.Rupal S. AminGCGW 17 April 2009

  17. Need to measure mirror absorption ratios Heat and cool interferometer mirrors FEM of drumhead mode freq. evolution Results in frequency shifts f (Hz) f0 fhot Step 1: Model actual heating LIGO-G0900358.Rupal S. AminGCGW 17 April 2009

  18. Thermal issues: eLIGO LIGO-G0900358.Rupal S. AminGCGW 17 April 2009

  19. Resonant Sideband Imbalance Still Here Problems with cut and paste LIGO-G0900358.Rupal S. AminGCGW 17 April 2009

  20. -2003-2004 LHO ilog Indicate poor power build-up PRIOR to mirror replacement Due to excessive thermal lensing Sideband overlap and imbalance NOT controlled -LLO Phase Cam. (A. Gretarsson LLO ilog 2004) Resonant Sideband Build-up Pwr PRM Pwr in S. Ballmer (MIT thesis, 2006) Thermal Issues: iLIGO LIGO-G0900358.Rupal S. AminGCGW 17 April 2009

  21. Effects on Strain Sensitivity • Decrease arm cavity gain  Arm length sensing • Decrease PRM carrier gain  Shot noise • Decrease PRM SB gain  Locking and alignment precision • Increase total carrier contrast defect  Shot noise R. Lawrence (MIT Thesis, 2003) Thermal issues: iLIGO LIGO-G0900358.Rupal S. AminGCGW 17 April 2009

  22. Objective • Control thermal aberrations with auxiliary lasers • Reduce optical noise • Improve high frequency sensitivity • Reduce down time with pre-heating Thermal Compensation System LIGO-G0900358.Rupal S. AminGCGW 17 April 2009

  23. Result: Absorption ratio for ITMX = 3.5 ppm ITMY = 5 ppm +/- 10% Step 1: Result LIGO-G0900358.Rupal S. AminGCGW 17 April 2009

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