1. Thermal Compensation Review David Ottaway LIGO Laboratory MIT

2. Advanced LIGO Technical Review2 Overview 1. Overview of Problem 2. Road map for design choices (Set by other systems) 3. Summary of current results from subscale tests and modeling 4. Current known unresolved issues 5. Plans and resources required for next year

3. Advanced LIGO Technical Review3 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: SapphireFused Silica Thermo-optic126 Thermal Expansion0.81.6 Elasto-optic Effect0.2- 0.3

4. Advanced LIGO Technical Review4 Thermal Comparison of Advanced LIGO to LIGO 1 ParameterLIGO I LIGO II Sapphire LIGO II Silica Units Input Power612580W PRC Power 0.42.11.3kW Arm Cavity Power 26850530kW Substrate Absorption 510-40 (30)0.5-1 (0.5)ppm/cm Coating Absorption 0.5 0.1- 0.5(0.5) ppm

5. Advanced LIGO Technical Review5 Effect on Advanced LIGO Interferometers

6. Advanced LIGO Technical Review6 Adaptive Thermal Compensation Compensate for distortions in the substrates Essential for Advanced LIGO sensitivity to be realized Two parts to thermal compensation: 1. Coarse compensation of thermal lensing using heating ring and shielding 2. Small scale compensation using scanning CO 2 laser Accurate measurement of sapphire and fused silica thermal mechanical properties enable accurate models Good propagation models to set design requirements (Melody and FFT Code)

7. Advanced LIGO Technical Review7 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

8. Advanced LIGO Technical Review8 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

9. Advanced LIGO Technical Review9 Thermophysical Parameters Measurement (295-320 K) Sapphire (C and A axes) ParameterValueErrorUnits dn/dT7.20.5ppm/K aa 5.10.2ppm/K cc 5.60.2ppm/K kaka 36.00.5W/m/K kckc 39.00.5W/m/K Fused Silica (Corning 7940) ParameterValueErrorUnits dn/dT8.70.3ppm/K  0.550.02ppm/K k th 1.440.02W/m/K

10. Advanced LIGO Technical Review10 Heater Ring Thermal Compensation

11. Advanced LIGO Technical Review11 Thermal Compensation of Point Absorbers in Sapphire

12. Advanced LIGO Technical Review12 Sub Scale Scanning Laser Test

13. Advanced LIGO Technical Review13 Scanning Laser Test Result Uncorrected Optic (6712 ppm scatter from TEM00)Corrected Optic (789 ppm scattered from TEM00)

14. Advanced LIGO Technical Review14 Predicted Effected of Thermal Compensation on Advanced LIGO

15. Advanced LIGO Technical Review15 Current Known Unresolved 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 Melody (Ray Beausoleil) 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)

16. Advanced LIGO Technical Review16 Plans and Resources for Next Year Plans: Work with the Gin Gin Facility to determine prototype Further modeling Design requirements (29 th Oct 2002) Preliminary design (14 th Apr 2003) Resources: Staffing: Mason (1/5 time), Ottaway (1/4 time) Ryan Lawrence graduating and leaving LIGO Resources: $50 K in MIT LIGO budget to build prototype