Thomas, Elli

We are interested in developing a way to measure the beam location on a test mass using camera images of the test mass. This can potentially be used for interferometer alignment.

This method is based on the PCal beam localization procedure. (See T1500039 for more details on the procedure.)

We used the Pcal camera on the ETMX to take a picture during full IFO lock. One can clearly see the red beam scattering off the test mass. To locate the center of the beam we fit a 2D gaussian to the beam scatter pattern in the image.  

The PCal camera is at a 10deg angle to the optic face.  We fit an ellipse to the image of the optic edge to work out its exact  orientation with respect to the camera. The we use this fit to locate the center of the optic, and the location of the center of the IR beam.  

Tonight we measure the IR beam location at {X,Y]=[-4.6mm,-20mm] +/- 5mm offset from the center of the optic.  This is a tentative result, we will put further thought into whether our beam fitting procedure has any sneaky assumptions in it.  
We also could reduce the uncertainty in this result by tweaking camera settings in order to better fit the optic edge.  The illuminator in BSC9 is on (it has been on since 19 December), turning this off would also help our cause.