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40m Log |
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Tue May 3 21:05:23 2022, yuta, Update, BHD, AS path alignment, removing a lot of green stuff 7x
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Wed May 4 13:09:42 2022, Anchal, Update, BHD, IMC table balanced again, IMC is locking, YARM is locking
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Wed May 4 15:08:59 2022, Tega, Update, BHD, XARM alignment to get flashing
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Wed May 4 18:52:43 2022, Tega, Update, BHD, POP beam too high at POP SM4 on the ITMX chamber
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Thu May 5 14:46:22 2022, Anchal, Update, BHD, POP beam height lowered, POP_SM4 raised
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Thu May 5 17:05:31 2022, Tega, Update, BHD, IMC & X/Y-arm alignment
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Mon May 9 18:43:03 2022, Anchal, Update, BHD, ITMX table layout corrected
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Mon May 9 18:49:05 2022, Tega, Update, BHD, Relocate green TRX and TRY PDs/cams/optics from PSL table to BS table 
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Tue May 10 15:46:38 2022, JC, Update, BHD, Relocate green TRX and TRY components from PSL table to BS table 
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Tue May 10 18:25:43 2022, Paco, Update, BHD, Green Transmission path
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Tue May 10 16:31:14 2022, Tega, Update, BHD, ITMX optlev return beam steered to QPD
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Fri May 6 13:48:34 2022, Anchal, Update, BHD, WFS loop instability fixed
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Thu May 12 19:55:01 2022, Tega, Update, BHD, AS path alignment 
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Thu May 12 20:11:18 2022, Anchal, Update, BHD, BHDBS Output beams steered out to ITMY table
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Thu May 12 20:24:29 2022, yuta, Update, BHD, POX and POY investigation
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Mon May 16 13:22:59 2022, yuta, Update, BHD, REFL and AS paths aligned at AP table 
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Mon May 16 19:14:17 2022, Anchal, Update, BHD, Camera set on AS path and BHDBS output path
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Tue May 17 18:43:38 2022, Anchal, Update, BHD, Placed SRM in ITMY Chamber
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Wed May 18 08:30:29 2022, Paco, Update, BHD, SRM OpLev
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Thu May 19 08:51:40 2022, Paco, Update, BHD, SRM OpLev
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Wed May 18 09:02:52 2022, Anchal, Update, BHD, WFS1 PD centered
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Wed May 18 17:23:15 2022, Anchal, Update, BHD, Placed PRM in BS Chamber
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Thu May 19 18:56:08 2022, yuta, Update, BHD, Current OSEM sensor values with all the suspensions aligned
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Thu May 19 19:05:59 2022, Anchal, Update, BHD, BS Chamber all work finished, BHD path setup
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Fri May 20 20:03:48 2022, Paco, Update, BHD, ITMY chamber work finished - LO and AS overlapped 
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Mon May 23 13:16:59 2022, Paco, Update, BHD, End of vent - checks  
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Tue May 24 15:21:13 2022, Anchal, Update, BHD, Freeswing tests of new SOS started
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Message ID: 16866
Entry time: Thu May 19 19:05:59 2022
In reply to: 16863
Reply to this: 16868
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Author: |
Anchal |
Type: |
Update |
Category: |
BHD |
Subject: |
BS Chamber all work finished, BHD path setup |
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[Anchal, Paco, Yuta]
BS Oplev Path
- The changed position of PRM (40m/16863) meant that BS oplev path is getting clipped by the PRM SOS tower.
- We had to move BSOL ~ 16 cm North and ~ 1.7 cm East.
- This means that the BS Oplev input beam is now coming behind TT2 instead of infront of it.
- We also had to align the beam such that input and returning beam are colinear.
- This meant we, had to change the mount of the upstream beamsplitter in the in-air table so that we can use that for separating the return beam.
- Again, we should order 2 inc visible BS for this path.
- Half of the return beam is making its way all the way back to the laser head. I'm not sure if that can be an issue for our oplev loops.
- We kept the SRM Oplev path same using irises on the table.
PRM Oplev
- Again, due to changed position of PRM and BS Oplev, it became very hard to setup oplev for PRM.
- We found a special position which allows us to catch returning beam through the center of the window.
- But this returning beam is not prompt reflection from PRM, it is reflection of the HR surface.
- We are hitting about ~5 mm from the edge of PRMOL mirror (because we cannot move the mirror anymore south to avoid clipping BS and SRM input oplev beams)
- We put in a 1.1m focal length lens in the input beam to narrow the beam on PRMOL so that it doesn't clip
- We did not put any lens for the return beam. The sensitivity of this oplev might be low due to slighlty bigger beam on the QPD than others (SRM, BS). We can revisit and insert a lens later if required.
Interferometer alignment and PRM alignment
- The work on BS table did not change the table balance much. We got back the alignment pretty much instantly.
- We were able to maximize the arm transmissions.
- Then we used a beam card with hole to check for reflection from PRM and used PRM (mostly pitch correction) to get the return beam back in same way.
- This recovered REFL beam on the camera. We used REFLDC signal to align PRM better and maximized it.
- We centered BS, SRM and PRM oplevs after this point.
LO beam mode correction and spatial overlap
- We tried changing the distance between LO3 and LO4 to get a better output LO beam.
- We also tried to swap the LO4 mirror with the spare mirror but we had the same result.
- Eventually, we decided to move LO3 back to East and LO4 to the west edge of the table. This made the beam sizes comparable.
- Future exercise: We think that LO1 or LO2 might be significantly off-spec in their ROCs which might cause this issue.
- We should rerun the calculations with the ROC values of LO1 and LO2 written in the datasheets and figure out the correct LO3-LO4 length required.
- We can make this change in the next vent if required.
- After the beam sizes were looking approximately similar but more iterations of changing length and realigning are required.
Remaining tasks before pumpdown
- Push/pull too bright/dark OSEMs in the SOSs (40m/16865).
- Finish LO beam mode correction and spatial overlap.
- Center all oplevs, note all beam positions on camera, and note down all DC PD values at proper alignment.
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