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Entry  Thu Mar 15 04:04:23 2012, Koji, Configuration, Locking, PRC Matching issues P3150910.jpgP3150902.jpgP3150906.jpgP3150907.jpgP3150900.jpg
    Reply  Thu Mar 22 17:35:59 2012, kiwamu, Update, Locking, mode profiles of the POP and POX beams : not bright enough 
Message ID: 6421     Entry time: Thu Mar 15 04:04:23 2012     Reply to this: 6437
Author: Koji 
Type: Configuration 
Category: Locking 
Subject: PRC Matching issues 

Kiwamu and Koji

We found that the intra-cavity mode of the PRC is not round although it was obvious even with the DARK and REFL port images.
We need to review the mode matching situation.

In order to look at the PRC intra-cavity mode, we reconfigured the POP CCD.

If we look at the beam reflected from the Michelson, the beam is round. However, the PRC intra-cavity mode can never be round
in any resonant conditions. (Pict 1, 2, and 3, for the sideband resonant, carrier resonant conditions and another carrier resonant
one, respactively). Particularly the mode of the carrier resonant case is very unstable and always changing.

P3150902.jpg

P3150906.jpgP3150907.jpg

By misaligning the PRM, we can compare between the spot directly reflected from the Michelson and the one after additional round trip in the PRC (Pic 4).

They looks round, but it was obvious the secondary reflection is dimmer and larger (Pic 5). The intensity difference corresponds to the factor RPRM RMI
(i.e. product of the reflectivities for the PRM and MI). It can be understand if the dimmer spot looks smaller due to the artifact of the CCD. But it is opposite.

This may mean the mode matching is not correct. We are not sure what is not right. This could be just an incorrect incident beam, the curvature error of the PRM,
beam is distortec by the TT mirrors, or some other unknown reasons.

More precise analysis can be done with quantitative analysis of those two spots with Beamscan. This could happen tomorrow.

P3150910.jpgP3150900.jpg

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