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Entry  Thu Feb 24 17:42:00 2011, Aidan, Update, Green Locking, 15% of end laser sideband power transmitted through cavity 
    Reply  Sat Feb 26 02:33:16 2011, kiwamu, Update, Green Locking, sidebands on beatnote beat_note.png
       Reply  Sun Feb 27 09:43:59 2011, Aidan, Update, Green Locking, sidebands on beatnote 
       Reply  Sun Feb 27 13:09:56 2011, rana, Update, Green Locking, sidebands on beatnote 
Message ID: 4362     Entry time: Sun Feb 27 09:43:59 2011     In reply to: 4361
Author: Aidan 
Type: Update 
Category: Green Locking 
Subject: sidebands on beatnote 

Can we set up a fiber-PD on the end table to look at the beat between the "end laser IR beam" and the "PSL IR beam fiber-transmitted end beam"? 

We should see the same thing on that PD that we see on the green PD (plus any fiber noise and I'm not really sure how much that'll be off the top of my head). If we unlock the lasers from the arm cavity then the free-running noise of the lasers wrt to each other will probably swamp the 50kHz and 150kHz signals. Maybe we could lock the end laser to the free-running PSL by demodulating the beat note signal from the fiber-PD and then we could look for the extra sidebands in the IN-LOOP signal. Then we could progressively lock the PSL to the MC and arm cavity and see if the sidebands appear on the fiber-PD at some point in that process. 

It's possible that the 216kHz drive of the PZT on the Innolight is somehow driving up some sub-harmonics in the crystal. I think this is unlikely though: if you look at Mott's measurements of the Innolight PZT response, there are no significant PM resonances at 50 or 150kHz.



Other than the +/-216 kHz sidebands, we can see some funny peaks at +/- 50 kHz and +/-150 kHz.


Quote: #4351 by Aidan

So, on the vertex PD, the power of the 80MHz +/-200kHz sidebands should be around sqrt(0.15)*0.05 = 0.02 = 2% of the 80MHz beatnote.

Once we get the green and IR locked to the arm again, we're going to look for the sidebands around the beatnote.


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