Reports until 18:55, Thursday 03 October 2019
H1 PSL (ISC, PSL)
georgia.mansell@LIGO.ORG - posted 18:55, Thursday 03 October 2019 - last comment - 09:29, Thursday 17 April 2025(52292)
ALS pick-off update

Jason O, Georgia M

 

ECR 1900246

 

This week we have been in the PSL installing a new fiber pick-off for the ALS and squeezer lasers. The old pick off is on transmission of the reference cavity while the new one is on the ALS bypass, after the PMC. Peter K started this work a month ago (alog 51610).

 

We currently have installed a mode matching lens (f=200mm f=150mm) between the beam splitter and the steering mirror, and achieved ~73% ~82% power transmission through the fiber so far.

 

We think we can get more light through the fiber by tweaking the mode matching lens position. We will need to go back into the PSL again to finish this work and feed the fiber and photodiode cable out to the rack. 

 

Once the layout is finalised I'll update the psl table layout document (D1300348).

 

Modifications to the fiber distribution box are also ongoing.

Comments related to this report
jeffrey.kissel@LIGO.ORG - 12:38, Wednesday 16 April 2025 (83957)
Link 

J. Kissel for J. Oberling

As we work through the history of the ALS pick-off path in order to augment it and create an SPI pick-off path within (ECR E2400083), Jason shared a screenshot of his beam-profile model from JAMMT when he suggested placement of ALS-L5 (the f=150 mm lens mentioned abov). I post it here for historical reference.

For the record the fiber collimator used in the ALS/SQZ distribution pick-off is a Thor Labs F220 APC-1064.
Images attached to this comment
jason.oberling@LIGO.ORG - 13:18, Wednesday 16 April 2025 (83958)
Link

So there is clarity here for future reference, I created that quick-and-dirty JamMT model from the as-built LHO PSL table layout in March 2024, not when the ALS pickoff was installed in October 2019.

Further, the SPI pickoff install team discovered that the as-built PSL table layout has had an error in the ALS beam path since the IO side of the PSL table was installed during aLIGO PSL installation in the 2012 timeframe.  The beam line from ALS-M1 to ALS-M2 is misplaced on the as-built layout; the layout shows the beam line along table row 23 but in reality it is along table row 25, 2 inches further +Y (using the IFO coordinate axes) than the layout indicates.  Corey took pictures of the PSL table in 2013 (D1301029) that show ALS-M1 in line with the 2nd ISS turning mirror, which is along table row 25.  Because of this the distances shown on the JamMT model are too short by 2 inches, rendering the beam waist size and location results given by that model incorrect.  In addition, the overall ALS path is longer by 4 inches than the as-built layout implies. 

I will correct this when I update the PSL as-built layout after the SPI team is done.

jeffrey.kissel@LIGO.ORG - 09:29, Thursday 17 April 2025 (83970)
Link 

Right! The mode-matching model that Georgia put together can be found in an other file in the ECR E1900246, specifically PMCtoFiberMM.png.