Thermal Compensation NSF

1. Thermal Compensation NSF David Ottaway LIGO Laboratory MIT

2. Overview • Labs and people • Adaptive thermal compensation overview and current conceptual design • Thermal loading effects on Advanced LIGO • Road map for design choices (Set by other systems) • Summary of current results from subscale tests and modeling • Current issues • Plans and Resources Required Advanced LIGO Technical Review G020467-00-R

3. People and Labs LIGO MITDave Ottaway, Ken Mason, Mike Zucker and Ryan Lawrence LIGO Caltech Bill Kells, Erika de Ambrosia and Phil Willems Stanford Ray Beausoleil (Melody development) UWA* David Blair, Bram Slagmolen and Jerome Degallaix ANU* David McClelland UA* Peter Veitch, Jesper Munch and Aiden Brooks * Gin Gin Facility contributors and members of the Australian ACIGA collaboration Advanced LIGO Technical Review G020467-00-R

4. Adaptive Thermal Compensation • Due to high circulation power, significant power will be absorbed in the test masses => Significant thermal distortions • Absorption characteristics unlikely to be sufficiently accurately known to allow an Initial LIGO 1 Style Point design • NEED Active Compensation of the mirrors • This sub-system provides such a means of compensation Advanced LIGO Technical Review G020467-00-R

5. ITM Compensation Plates PRM ITM SRM Conceptual Design • Design utilizes a fused silica suspended compensation plate • Actuation by a scanned CO2 laser (Small scale asymmetric correction) and nichrome heater ring (Large scale symmetric correction) • No direct actuation on ITMs for improved noise reduction, simplicity and lower power (Sapphire) Advanced LIGO Technical Review G020467-00-R

6. Thermal Distortion • Absorption in coatings and substrates => Temperature Gradients • Temperature Gradients => Optical path distortions • 3 Types of distortions, relative strengths of which are shown below: Advanced LIGO Technical Review G020467-00-R

7. Thermal Comparison of Advanced LIGO to LIGO 1 Advanced LIGO Technical Review G020467-00-R

8. Effect on Advanced LIGO Interferometers (Melody Prediction) Advanced LIGO Technical Review G020467-00-R

9. Requirements that flow from other systems • Core Optics (Down select) Sapphire -Significant possible inhomogeneous absorption -> Small spatial scale correction (scanning laser) -Large thermal conductivity -> Small amount of coarse compensation (ring heater) on compensation plates Fused Silica -Poor thermal conductivity and homogenous absorption (ring heater) • DC or RF read out scheme (Down select) -Reduces dependence on sidebands, might affect design requirements • Wavefront Sensing (LIGO 1 experience, not fully understood) -High spatial quality sidebands are probably necessary for accurate alignment control, may negate the effect of read out scheme Advanced LIGO Technical Review G020467-00-R

10. Summary of Subscale Experiments and Modeling • Accurate measurements of fused silica and sapphire material properties • Experimental demonstration of shielded heater ring coarse spatial correction • Experimental demonstration of scanning CO2 laser fine spatial scale correction • Accurate models of Advanced LIGO Interferometers style interferometer using Melody and finite element analysis (Femlab), (Thermal modeling without SRM) • Scaling from subscale to full scale understood • Work done by Ryan Lawrence Advanced LIGO Technical Review G020467-00-R

11. Thermophysical Parameters Measurement (295-320 K) Advanced LIGO Technical Review G020467-00-R

12. Heater Ring Thermal Compensation Advanced LIGO Technical Review G020467-00-R

13. Thermal Compensation of Point Absorbers in Sapphire Advanced LIGO Technical Review G020467-00-R

14. Sub Scale Scanning Laser Test Advanced LIGO Technical Review G020467-00-R

15. Scanning Laser Test Result Uncorrected Optic (6712 ppm scatter from TEM00) Corrected Optic (789 ppm scattered from TEM00) Advanced LIGO Technical Review G020467-00-R

16. Predicted Effected of Thermal Compensation on Advanced LIGO Advanced LIGO Technical Review G020467-00-R

17. Current Issues • Gravitational wave sideband distortion and its effect on sensitivity. Generated within the cavity no distortion nulling due to prompt reflection. Greater understanding through incorporation in through new improvements in Melody • Experimental test to confirm Melody • Fabry-Perot mode size change due to input test mass surface deformation => Spot size change (actuate on arm cavity faces) • Accurate 2D absorption maps of Sapphire to aid in actuator selection (negative or positive dN/dT actuator plates) • Development of full scale prototype Advanced LIGO Technical Review G020467-00-R

18. Research and Engineering Plans • Set design requirements utilizing Melody • Already started with the work of Ryan Lawrence • Develop and test full scale prototype • Performance measured using Shack-Hartmann sensor (LIGO) • Diffraction limits do not allow full spatial test on bench-top • Concurrently experimentally validate Melody • Subscale high power tests in the Gin Gin Facility (ACIGA) • Measurements from initial LIGO (LIGO) • Develop alternative instrumentation strategies • Alternative instrumentation strategy (Hartmann Sensor) (ACIGA) • Multi-Pixel sensor (Phase Camera) preliminary experience gained at LIGO MIT (LIGO) • Confirm final design Advanced LIGO Technical Review G020467-00-R

19. Schedule Advanced LIGO Technical Review G020467-00-R

20. Summary of Costs • Labor for development • Scientist 5.8 FTE Years • Engineer 4.2 FTE Years • Grad Student 0.7 FTE Years • Technician 2.7 FTE Years $669,789 • Contract labor for manufacture • Technician $336,510 • Equipment for Lab Tests $145,000 • Equipment for Installation $440,691 • Total (Inc Overhead & Contingency) $3,054,886 Advanced LIGO Technical Review G020467-00-R