I turned on the Ring Heater this morning to a nominal 30W of electrical power. We've yet to fully determine the ratio of the radiated power to electrical power, but the most recent number is approximately 2.5W radiated power per 6W electrical power.

I measured the spherical power of the HWS beam -  probing the ETM thermal lens and surface deformation and compared it to the results from a simple COMSOL model of the predicted thermal lens + surface deformation [no fitting]. The results are shown in the attached plot. Bear in mind that the scale of the predicted model will be affected by the delivered power (dependent on the radiated to electrical power ratio) and that the HWS is still operating on a nominal calibration for the optical system - rather than a measured calibration. 

The results are quite similar but there are obvious differences in the time constant. At the moment I would put that down to the simplicity of the COMSOL model - it doesn't include the flats on the sides of the ETM, or the reaction mass or the time constant associated with the ring heater itself.

However, this is the first real aLIGO measurement of thermal lensing with the HWS.

Caution: this is not solely the surface curvature of the ETM - the optical path distortion from the thermal lens is roughly 10x larger than that of the surface curvature.

10-Aug-2012 11:34AM - replaced plot. I had added the incorrect sign to the surface deformation in the model. I've fixed this.