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

      • See https://dcc.ligo.org/LIGO-D1300231

      • See, also https://gwwiki.icrr.u-tokyo.ac.jp/JGWwiki/KAGRA/Subgroups/IOO/OutputTables/Optics for in-air optics assembly

  • 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+