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Thermal Compensation Review. David Ottaway LIGO Laboratory MIT. Overview. Overview of Problem Road map for design choices (Set by other systems) Summary of current results from subscale tests and modeling Current known unresolved issues Plans and resources required for next year.

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Thermal Compensation Review

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Thermal compensation review

Thermal Compensation Review

David Ottaway

LIGO Laboratory




  • Overview of Problem

  • Road map for design choices (Set by other systems)

  • Summary of current results from subscale tests and modeling

  • Current known unresolved issues

  • Plans and resources required for next year

Advanced LIGO Technical Review

Thermal distortion

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

Thermal comparison of advanced ligo to ligo 1

Thermal Comparison of Advanced LIGO to LIGO 1

Advanced LIGO Technical Review

Effect on advanced ligo interferometers

Effect on Advanced LIGO Interferometers

Advanced LIGO Technical Review

Adaptive thermal compensation

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

    CO2 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)

Advanced LIGO Technical Review

Requirements that flow from other systems

Requirements that flow from other systems

  • Core Optics (Down select)


    -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

Summary of subscale experiments and modeling

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

Thermophysical parameters measurement 295 320 k

Thermophysical Parameters Measurement (295-320 K)

Advanced LIGO Technical Review

Heater ring thermal compensation

Heater Ring Thermal Compensation

Advanced LIGO Technical Review

Thermal compensation of point absorbers in sapphire

Thermal Compensation of Point Absorbers in Sapphire

Advanced LIGO Technical Review

Sub scale scanning laser test

Sub Scale Scanning Laser Test

Advanced LIGO Technical Review

Scanning laser test result

Scanning Laser Test Result

Uncorrected Optic (6712 ppm scatter from TEM00)Corrected Optic (789 ppm scattered from TEM00)

Advanced LIGO Technical Review

Predicted effected of thermal compensation on advanced ligo

Predicted Effected of Thermal Compensation on Advanced LIGO

Advanced LIGO Technical Review

Current known unresolved issues

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)

Advanced LIGO Technical Review

Plans and resources for next year

Plans and Resources for Next Year


  • Work with the Gin Gin Facility to determine prototype

  • Further modeling

  • Design requirements (29th Oct 2002)

  • Preliminary design (14th Apr 2003)


  • 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

Advanced LIGO Technical Review

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