madison.simmonds@LIGO.ORG - posted 16:50, Tuesday 14 April 2026 (89885)
Changed fibre for EX HWS
Madi, Camilla, TJ
Had a look with the card at both the HWS beam and the ALS back reflection in the HWS line
Both 50um and 200um fibre attached
Took power-meter measurements
For 50um fibre, only ~20uW out of the collimator, and lower than ambient light coming back to HWS camera
For 200um fibre, 247uW out of collimator
14.45uW of ALS at HWS camera
78.6nW of HWS at HWS camera
49.3nW measured with no beam on HWS camera
Also misaligned ETM, and watched the ALS beam, and the HWS beam move off the HWS camera, confirming that what we were seeing was indeed returned light from the ETM
With the HWS beam, there was an artefact that didn't move with the ETM misalignment - theorise this is a stray beam reflection from optics on the table onto the HWS camera
The return ALS beam is very strangely shaped - before labelled the 'mickey mouse ears'. To me it looked like a 1,0 mode, but with one lobe larger than the other. Interested to see how much similar the HWS return is to that shape?
Checked HWS alignment towards ETM - pretty bad, not very centred. Off in pitch and yaw
Checked co-alignment of HWS and ALS towards HWS camera - not great