1. November 2006 ITM Heating Measurements at LLO
Sam Waldman & Phil Willems
Caltech
December 4, 2006

2. Our Puzzling and Inconclusive Results
ITMX absorption ~10 ppm
ITMY absorption <1 ppm
Measurements are not internally consistent between ITMX and ITMY

3. Technique Same technique as at LHO: Small differences;
Install telescopes and cameras at POX and POY to measure beam spot size with Michelson lock
Calibrate spot size change using TCS central heating
Run IFO at high power without TCS until thermalized, then break lock down to Michelson and measure spot size change
Small differences;
Spiricon software used instead of BeamView
Telescopes were improvised on the ISCT tables

4. Mystery 1: TCS Calibration Data
The relative spot size changes were very similar at the cameras, but the applied heat was 85mW to ITMX and 13mW to ITMY. Measured ITM tilt sensitivity still leaves factor 2.3 discrepancy between ITMX and ITMY.

5. Mystery 2: Very Different Absorptions
ITMX pitch ITMX yaw
TCS
IFO
(~10ppm)

6. Mystery 2: Very Different Absorptions
ITMY pitch ITMY yaw
TCS
IFO
(<1ppm
Time constant is Faraday-like, and calibration is only 13mW)