Gerardo, Keita, Jim, Camilla, Sheila
We installed the OPO pump diamond fiber this morning, but the transmission is about 60%. The input power was fluctuating during our measurements, but the first measurement indicated 60% transmission for the feedthrough and 50% transmission from the table to the feedthrough. The second measurement of the entire chain gave 27% transmission of the whole chain.
There is a green glow from the fiber right inside the feedthrough. I will attach a to photo to this log soon.
1. We decided to align in-chamber things with what we have.
There are things that can be done regardless of our decision to do something to the pump fiber (or not).
2. Cleaning the in-air side of the feedthrough improved the throughput to 76%.
But it's still glowing.
The feedthrough connector doesn't have a mating sleeve, it's just the female connector directly built into the flange and the fiber is deep inside a hole, so we couldn't use the fiber microscope to inspect. I used NEOCLEAN cleaner without FC plug adaptor, directly stuck the cleaner head into the hole, and pushed twice to clean.
After this, 1.44mW total was measured in chamber (sum of two polarizations) while the in-air fiber delivered 1.9mW, i.e. ~76% throughput.
(BTW there was a picture shot on Jun 09 in alog 59175 that shows that this same fiber had some green glow from the start, but it sounds as if it was dimmer than now. That alog noted "the PEEK shell looked somewhat greener than the old fiber" where the "old fiber" refers to the FCGS fiber. If it was as bad as Sheila's picture in the parent alog of this one I'd have used different words.)
3. Alignment (and probably the mode matching) of the pump beam changed.
I noticed that the pump beam was too big and the alignment was totally off. Reseating the fiber to the collimator eventually got the size and alignment back to what seemed to be in a reasonable ball park. Looking at the green transmission while scanning OPO, we adjusted the collimator mostly in YAW. It improved some but it's still not well aligned, probably we'll have to touch a steering mirror too. And we need a DCPD to work to refine alignment anyway, so this will have to come later.
This won't interfere with our rough alignment to bring the green beam reflection out through the viewport simulator.
4. FC path retro reflection mirror was placed 128mm from A:M3
We injected IR and scanned the OPO slowly to see the flashing, which worked. We placed a retro mirror where the waist position would be in the FC path and started aligning this mirror. We'll continue tomorrow.
Above where Keita wrote that the retro reflector was 128mm from A:M3, that was a typo, it is placed 178mm from A:M3 which is correct. Lee Camilla and Georgia just confirmed this with a ruler in the chamber, and 60276 confirms that we have the expected beam waist leaving the VIP towards the QPD path.