= 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 [[https://www.thorlabs.com/thorproduct.cfm?partnumber=BA1/M|Thorlabs BA1/M]] with [[https://gwdoc.icrr.u-tokyo.ac.jp/cgi-bin/private/DocDB/ShowDocument?docid=8429|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+