In-vac PD/QPD layout meeting 2025/03/31
Time: Mar 31, 2025 14:00-14:45
Participants: Ray-Kuang Lee, Huali Chen, Ryan Yang, Yoichi Aso, Yuta Michimura
Zoom meeting
Minutes
- REFL (Ryan)
- In-vac RF QPD path almost finished, need info for RF PD path
- RF PD path
- Beam size at RF PD should be around 0.1 mm radius. But avoid putting RF PD at the waist to avoid PD reflected beam mode-matching to the main beam and causing scattered light noise.
Footprint for RF PD is 125 x 58 mm https://gwdoc.icrr.u-tokyo.ac.jp/cgi-bin/private/DocDB/ShowDocument?docid=16111
- RF QPD path
- Waist size of 0.25 mm radius, and beam radius of sqrt(2)*0.25 mm at RF QPDs are consistent with in-air design
- Pedestal size
- Right now using 78 mm dia pedestal, but for 4 inch height optics, we will not use this.
- Since we don't have the design yet, let's copy LIGO design for 4 inch height optics.
Mounting base can be Thorlabs BA1/M with 20 mm dia. posts
- Slightly tilt RF PD and RF QPD so that we can damp the PD/QPD reflected beams
- Let's aim for 800 mm dia. optical breadboard size inside the PD chamber
- AS (Huali)
- Updated the layout based on the comments from the last meeting (OSTM wedge, periscope and distance traveled within periscope, beam diverter)
- To avoid AS RF beam being too close to OMC REFL RF QPD 2, we can play with moving optics slightly
- Clearance of 2 cm should be enough
- No periscope is needed for squeezing injection (to-be-viewport flange is already 210 mm heigh)
- squeezing beam require 78 mm dia. pedestal
A/I
- Reduce the size of the breadboard to 800 mm dia, and add RF PD layout for REFL [Ryan]
- Slightly update the layout to have more space between AS RF beam and OMC REFL RF QPD [Huali]
- Check IFI chamber layout if POM2 the beam is hitting the center of POM2 [Michimura]
- Next meeting: TBD on the week of April 21+