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Entry  Mon Oct 17 11:40:44 2011, Koji, Update, LSC, REFL165 removed from the table 
    Reply  Mon Oct 17 22:20:42 2011, Koji, Update, LSC, REFL165 removed from the table 
       Reply  Tue Oct 18 10:04:41 2011, Koji, Update, LSC, REFL165 removed from the table REFL165_original.pdfREFL165_new.pdfREFL165_schematic_111017_KA.pdf
Message ID: 5685     Entry time: Tue Oct 18 10:04:41 2011     In reply to: 5681
Author: Koji 
Type: Update 
Category: LSC 
Subject: REFL165 removed from the table 

The original REFL165 had ~50MHz/A dependence on the DC photocurrent.
The resistr R21, which was 2670 Ohm contrary to the original drawing, was replaced to 532 Ohm
to increase the feedforward gain by factor of 5.

The resulting dependence is reduced to ~0.5MHz/A although it has Q reduction of ~20% at 6mA.

Some concerns:

These transfer functions were measured between TEST IN and RF OUT while the diode was illuminated with the white light from a light bulb.

There looks some thermal effect on the resonant freq. If the white light illumination is suddenly removed, the bias compensation
is immediately removed but the resonance takes some time (~min) to come back to the original freq.

I am afraid that the light bulb gave too much heat on the surrounding PCB and lead unnecesarily high level dependence of the resonant freq on the DC current.

Or, if this thermal effect comes from the power consumption on the diode itself, we need to characterize it for aLIGO.

In order to check this, we need a test with the 1064nm illumination on the diode in stead of the light bulb.

Attachment 1: REFL165_original.pdf  50 kB  | Hide | Hide all
Attachment 2: REFL165_new.pdf  39 kB  | Hide | Hide all
Attachment 3: REFL165_schematic_111017_KA.pdf  125 kB  | Hide | Hide all
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