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Thermal Compensation Installation at LHO Dave Ottaway, Ken Mason, Stefan Ballmer- MIT Mike Smith, Phil Willems - Caltech Cheryl Vorvick, Gerardo Moreno, Daniel Sigg- LHO LSC Meeting, March 15-18 2004, LLO. ?. Initial LIGO Thermal Compensation Concept. CO 2 Laser. ZnSe viewport.

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Thermal Compensation Installation at LHO

Dave Ottaway, Ken Mason, Stefan Ballmer- MIT

Mike Smith, Phil Willems- Caltech

Cheryl Vorvick, Gerardo Moreno, Daniel Sigg- LHO

LSC Meeting, March 15-18 2004, LLO

LIGO Laboratory

initial ligo thermal compensation concept

?

Initial LIGO Thermal Compensation Concept

CO2 Laser

ZnSe viewport

Over-heat pattern:

Inner radius = 4cm

Outer radius =11cm

Over-heat correction aperture

Under-heat correction aperture

Inhomogeneous correction aperture

  • Imaging target onto the TM limits the effect of diffraction spreading
  • Modeling suggests a centering tolerance of 10 mm required to maintain good correction

LIGO Laboratory

thermal compensation projector
Thermal Compensation Projector

Annulus Mask Central Heat Mask No Masks

  • Intensity variations across annulus image due to small laser spot size
  • Modeling suggests that this should not be an issue
  • Projection optics work well
  • AOM distortion above 3W causes intensity centroid shift (these images all taken at 1 Watt CO2 laser power exiting AOM)

LIGO Laboratory

prm results mode images at as port both itms heated
PRM Results – Mode Images at AS Port (both ITMs heated)

RF sidebands-------------------------------------------------------------------------------------------------->|

no heating 30 mW 60 mW 90 mW

RF sidebands--------------------------------------------------------------------->| Carrier

120 mW 150 mW 180 mW (thru unlocked IFO)

LIGO Laboratory

prm results sideband buildup
PRM Results –Sideband Buildup
  • Max buildup at ~90 mW TC
  • TC increased in 30 mW steps
  • IFO is sideband locked PRM with wavefront sensing

LIGO Laboratory

prm optical gain during heating
PRM Optical Gain during heating
  • Maximum gain at ~90 mW central heating
  • Same heating optimizes RF sideband buildup
  • Same heating makes RF sideband mode resemble carrier mode

LIGO Laboratory

full interferometer results
Full Interferometer Results
  • Interferometer locked at 1 Watt
  • 90 mW central heating applied to both ITMs
  • Central heating reduced
  • Maximum power with 45 mW heating
  • ?? No change in AS_DC throughout

LIGO Laboratory

summary of results
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

prm asymmetric heating
PRM Asymmetric Heating
  • Maximum achieved with 120 mW on ITMy only
  • SPOB build-up is the same gotten with common heating
  • ITMx requires 200 mW to maximize SPOB to lower value; some asymmetry observed in mode structure

LIGO Laboratory

issues to resolve
Issues to Resolve
  • Errors/difficulties in installation reduce the viewport aperture- annulus heating not fully functional yet
  • Different behavior of ITMx and ITMy
  • Optimum compensation occurs with 90mW central heating, yet models predict less than half this
    • Tests show 90% of CO2 laser power is absorbed by ITM
    • Misalignment of CO2 laser beam cannot explain discrepancy

LIGO Laboratory