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Entry  Fri Sep 12 00:40:23 2014, Jenne, Update, LSC, DRMI locking 
    Reply  Fri Sep 12 11:25:42 2014, Koji, Update, LSC, DRMI locking 
       Reply  Fri Sep 12 12:00:59 2014, ericq, Update, LSC, DRMI locking 
    Reply  Fri Sep 12 14:11:17 2014, ericq, Update, LSC, DRMI locking 7x
       Reply  Wed Sep 17 15:40:00 2014, ericq, Update, LSC, DRMI locking dcAngleDiff_srcL.pdfdrfpmiVertexSensing.zip
          Reply  Tue Sep 23 17:37:10 2014, ericq, Update, LSC, DRMI locking SRCcorrection.pdf
             Reply  Wed Sep 24 11:02:38 2014, manasa, Update, LSC, Moving SRM 
                Reply  Thu Sep 25 11:33:41 2014, Jenne, Update, LSC, POY alignment laser 
Message ID: 10514     Entry time: Wed Sep 17 15:40:00 2014     In reply to: 10502     Reply to this: 10527
Author: ericq 
Type: Update 
Category: LSC 
Subject: DRMI locking 

I have not had any success the past two days in getting an interferometric measurement of the SRC length. 

So, the question posed at today's meeting was: "How precisely do we need to change the SRC length to be able to lock the DRMI on 3F"

The two ways I could think to quantify this are:

  • How much MICH -> [S,P]RCL cross coupling is ok?
  • How much [S,P]RCL ->  MICH cross coupling is ok?

REFL33 should have its phase set to put PRCL along I, and REFL165 should have SRCL along I, so the simulation result that matters is the angle of MICH in these planes. The cross couplings are then given by the appropriate trigonometric projections. In the following plots, I used 10% as the acceptable cross coupling in either direction. 

Result:

dcAngleDiff_srcL.pdf

Thus,

  • To limit the MICH -> [S,P]RCL coupling to 10%, we must hit the ideal length within +- 1.2cm.
  • To limit the SRCL -> MICH coupling to 10%, we must hit the ideal length within +- 2mm.
  • It doesn't look like we can get the REFL33 angle totally to 90 degrees, REFL165 looks more promising.

Code (finesse + pykat + ipython notebook) and plots are attached. 

Attachment 2: drfpmiVertexSensing.zip  369 kB
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