= Type B Dummy BS Redesign - Info for discussion at VIS Meeting 6/3/2016 =

To test an optical lever that measures both position and angle, Akutsu-san would like a much larger mirror at the center of the dummy BS. The current design is [[http://gwdoc.icrr.u-tokyo.ac.jp/cgi-bin/private/DocDB/ShowDocument?docid=4820| D1604820]]. It uses three Sigma-Koki [[https://www.global-optosigma.com/jp/Catalogs/gno/?from=page&pnoname=TFA%2FTFAN%2FTFAQ%2FTFAQN-C&ccode=W3010&dcode=W3010-1&gnoname=TFA-30C05-4|TFA-30C05-4]] 30 mm diameter mirrors, one at the top on one side, and two at the center on opposite sides.

== Cheap, Quick Plan ==
 
Glue a Thorlabs [[https://www.thorlabs.co.jp/thorproduct.cfm?partnumber=PF30-03-P01|PF30-03-P01]] 3" x 3/4" mirror (or similar) into the recess in the middle of the current dummy BS. (Mirror is 76.2+0-0.1 mm diameter, whereas recess is 76.2+0.3-0 mm.) Glue a matching metal blank with a vent hole into the recess on the other side. 

=== Advantages ===

 * Could probably do the gluing of the mirror and blank after the gluing of the flags and prisms. (The OSEM side would be easy, opposite side would be hard due to the mirror box, but probably not impossible. We might have to do it during hanging.)
 * Mirror is readily available for ￥46,280 from Thorlabs. 
 * Metal blank would be cheap and quick to make.

=== Disadvantages ===

 * There would be a step of about 11.1 mm between the face of the dummy BS and the face of the 3" mirror. (Mirror is 19.1 mm thick, recess is 8 mm deep.)
 * The dummy BS would be slightly heavier than the real BS. The 3" x 3/4" mirror and the blank would each weigh 190 g, whereas the current mirror adapter and small mirror weigh 86+9 = 95 g so we'd have to remove 2*(190-95) = 190 g from the IM. The moment of inertia would also be slightly off.

== Quicker, Cheaper Plan - Akutsu ==

Install a polished stainless steel insert on each side.

=== Advantages ===

 * As above, but probably even easier to install. 

 * Could easily be bigger than 3" with only a tiny step if mushroom-shaped.

=== Disadvantages ===

 * Is the surface really good enough for an OL with several meter arms???

== Comprehensive Redesign ==

Get Fabian to redo the design from the beginning.

=== Advantages ===

 * Could use a mirror even bigger than 3", e.g., 4" [[http://www.thorlabs.co.jp/thorproduct.cfm?partnumber=PF40-03-P01|PF40-03-P01]] (￥68,380). Or if flatness is not so critical, perhaps even a large, thin, flat mirror such as Sigma-Koki [[http://www.global-optosigma.com/en_jp/Catalogs/gno/?from=page&pnoname=TFAEFL&ccode=W3177&dcode=&gnoname=TFAEFL-200S06-P|TFAEFL-200S06-P]].

=== Disadvantages ===

 * Expensive - would probably need re-making or extensive re-machining of existing dummy BS main body.
 * Slow - redesign and remaking would probably take longer, and gluing of flags scheduled for Wednesday 6/8 would have to be postponed.