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LIGO Laboratory Thermal Compensation Project: Initial Results and Implementation

This project presents the preliminary outcomes and execution of thermal compensation techniques at the LIGO Laboratory, focusing on CO2 laser and ZnSe viewport. The study includes over-heat and under-heat corrections, image target limitations, and asymmetric heating effects. Results highlight image intensity variations, wavefront sensing control, and optical gain adjustments during heating processes. The implementation also involves annulus masks, central heat masks, and heating reduction strategies to optimize system performance.

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LIGO Laboratory Thermal Compensation Project: Initial Results and Implementation

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  1. Thermal Compensation Initial Results Dave Ottaway Mike Smith, Phil Willems, Cheryl Vorvick, Gerado Moreno, Ken Mason, Stefan Ballmer and Daniel Sigg LIGO Laboratory

  2. ? Initial LIGO Thermal Compensation Concept CO2 Laser ZnSe Viewport Over-heat pattern Inner radius = 4cm Outer radius =11cm Over-heat Correction Under-heat Correction Inhomogeneous Correction • Image target onto the TM limits the effect of diffraction spreading • Modeling by Phil Willems suggests a centering tolerance of 10 mm required LIGO Laboratory

  3. Thermal Compensation Implementation LIGO Laboratory

  4. Thermal Compensation Projector Annulus Mask Central Heat Masks No Masks • Intensity variations across the images due to small laser spot size • Modeling suggests that this should not be an issue • Projection optics work well • Images taken at 1 Watt CO2 Power (AOM distortion above 3 W) LIGO Laboratory

  5. Thermal Compensation Controls LIGO Laboratory

  6. PRM Results – Mode Images AS Port No Heating 30 mW 60 mW 90 mW 120 mW 150 mW 180 mW Carrier LIGO Laboratory

  7. PRM Results –Sideband build-up • Max ~90 mW • 30 mW Steps • Wavefront sensing controlled PRM LIGO Laboratory

  8. PRM Optical Gain during heating LIGO Laboratory

  9. Full Interferometer Results • Lock interferometer at 1 Watt • Apply 90 mW Common central heating • Started to reduce central heating • Max with 45 mW heating, then reduce heating to 22.5 mW • No change in AS_DC ???? LIGO Laboratory

  10. Summary of Results State SPOB GSB -------------------------------------------------------------------------------- State 2 cold 85 7.0 State 2 hot (90 mW CO2) 152 12.5 State 2 max (tRM / (1 - rRM rM rITM))2 14 -------------------------------------------------------------------------------- State 4 cold 160 13 State 4 warm (0.8W input) 190 16 State 4 hot (2.3W input, no TCS) 240 20 State 4 hot (0.8W input, 45mW CO2) 320 26.5 State 4 max (tRM / (1 - rRM rM))2 30 -------------------------------------------------------------------------------- LIGO Laboratory

  11. Asymmetric Heating • Maximum achieved with 120 mW on single ITM • SPOB build-up is the same as common heating LIGO Laboratory

  12. PRM Asymmetric Heating – Optical Gain LIGO Laboratory

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