[Aidan, Camilla]
We retro-reflected the HWS beam back to the CCD at various points along the beam path and discovered severe clipping from at least three optics.
We placed the retro-reflection mirror at points A, B and C. The return beams on the ETM are shown below. There is clearly clipping from around the final three optics before the HWS beam is injected into the ALS beam path.
Retro-reflection A
Retro-reflection B
Retro-reflection C
For reference, the beam is small around HWS-M2 and HWS-BS2, and largest around HWS-M1, HWS-M1A and HWS-M1B. The nominal beam size from the launcher is shown below:
[Aidan, Camilla]
Yesterday we replaced the 1" diameter optics, HWS-M1, HWS-M1A and HWS-M1B with 2" diameter optics. This involved removing the picomotor actuators. The return beam when the retro-reflector was placed at position C clean and showed no signs of diffraction or high frequency noise from spots or point defects.
We realigned the HWS probe beam to the ALS irises and got a beam back from the ETM. There was a return beam from ITMX on top of it. We tweaked the alignment to shift this off to the side and then out of the limiting aperture of the system so it disappeared. Unfortunately, the return beam from the ETM showed a lot of high frequency spatial noise still - point defects and mottled appearance.
We're going to do a retro-reflection from after the PBS to eliminate (confrm?) this as a source of noise or not.
Return beam from point C
Return beam from ETMX
1" optics before replacement
1" optics before replacement
2" optics replacement
2" optics replacement
