[Aidan, TJ, Danny]

Summary

We injected the HWS LED source and got a return beam from ETMX.

Details

Yesterday, the beam on the ETM HWS optics was quite large and couldn't be brought to a tight focus. I figured we'd get a cleaner (but less intense) beam with a smaller core fiber. So we swapped out the 200um 0.22NA core fiber for a 50um 0.22NA core fiber this morning. This allowed us to bring the beam to a much tighter focus around the first imaging lens (as required by the mode-matching solution).

1. We aligned two irises to the HWS LED beam in the HWS optical path
2. We ran the beam through the horizontal polarizer and injected it into the PBS.
3. We then aligned that transmission to the two ALS irises.
4. When we failed to get any reflection from the ETM, we turned on the ALS beam and adjusted the alignment of the two picomotor mirrors (manually, not with motors) so that the ALS beam returned back through the two irises in the HWS optical path.
5. We also used the ALS beam to align the final two mirrors and get the ALS beam onto the HWS.
6. Disengaging the ALS beam showed that the HWS LED source beam was returning onto the HWS as shown in the attached image. I think we see the aperture of the AERM in this image (it should be 813 pixels in diameter).

Tomorrow we're going to fine-tune the alignment and try a HWS measurement.

We'll post an image of the optical layout (with accompanying measurements of distances) tomorrow.

Return beam:

Beam size when propagated to test mass (T1700717-v6)