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Entry  Wed Oct 13 00:35:26 2010, kiwamu, Update, Green Locking, PSL beat note setup 
    Reply  Fri Oct 15 06:31:52 2010, kiwamu, Update, Green Locking, PSL beat note setup: part II 
Message ID: 3703     Entry time: Wed Oct 13 00:35:26 2010     Reply to this: 3727
Author: kiwamu 
Type: Update 
Category: Green Locking 
Subject: PSL beat note setup 

[ Kevin and Kiwamu ]

 We made the setup for the green PLL stuff on the PSL table.

 Now the two green beams are happily going to the RFPD.

Tomorrow we try to catch the beat note signal 

 

  - - - what we did

 * took the two light doors out from the OMC and the MC chamber in order to let the green light go through there.

 * using aluminum foils we covered the space between the OMC and the MC chamber in order to protect from dust

 * aligned the steering mirrors inside of the chamber because the height of the green light coming out from the chamber had been a little bit low at the PSL table.

 * at the PSL table we put several steering mirrors and a beam splitter which combines the two green lights

 * installed Hartmut's RFPD and applied -150V bias on it.

 * put a lens on each path of the green beam in order to make the beam size approximately the same at the RFPD

 * closed the light doors

 

- - - Notes

 * At the beginning, an output signal from the RFPD was pretty small ( less than 1mV at DC ), so I replaced a feedback resistor that was 241 Ohm by 24 kOhm.

   As a result the signal became about 10mV when the green lights go into the PD.

* Actually the power of the green beams are so weak.

  I measured them by using a Newport power meter, it said something like 4 uW for both of the green lights. 

  One of the reasons is that the transmitted light from the PMC which generates one of the green lights is already weak. It's about 480 mW ( while more than 600 mW was reflected by the PMC ! ).

  I am going to make sure if these numbers are reasonable or not.

 

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