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Entry  Wed Nov 2 10:41:47 2011, steve, Update, General, 2 spare heliax at the LSC rack 
    Reply  Wed Nov 2 19:32:20 2011, kiwamu, Update, LSC, POP22/110 installed 
       Reply  Thu Nov 3 14:25:52 2011, kiwamu, Update, LSC, PDA10A as POP22/110 : too small signal 
          Reply  Thu Nov 3 16:31:47 2011, kiwamu, Update, LSC, PDA10CF as POP22/110 : better 
Message ID: 5794     Entry time: Thu Nov 3 14:25:52 2011     In reply to: 5788     Reply to this: 5796
Author: kiwamu 
Type: Update 
Category: LSC 
Subject: PDA10A as POP22/110 : too small signal 

It turned out that the signal was too small with PDA10A to detect the 22 and 110 MHz RF sidebands.

The DC output coming out from it was about half mV or so (corresponding to few uW in laser power) when the PRCL was locked to the carrier.

This is because PDA10A is a silicon detector which is more sensitive to visible light than IR.

The reason we chose PDA10A was that it has relatively a large diode size of 1 mm in diameter.

However according to the data sheet the responsibility at 1064 nm is about 0.05 A/W which is sad.

I will replace it by PDA10CF, which is made from InGaAs and supposed to have 10 times bigger responsibility.

Though the diode size will be half mm in diameter, which may require another strong lens in front of it.

Quote from #5788
 The POP22/110 RFPD has been installed. It is PDA10A from Thorlabs instead of the usual home-made RFPD.
  + Fine alignment

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