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Entry  Thu Apr 8 10:17:52 2010, Alberto, Update, 40m Upgrading, REFL11 Noise Vs Photocurrent 2010_04_05_REFL11_ShotnoiseVsPhotocurrent.png
    Reply  Thu Apr 8 10:24:33 2010, Alberto, Update, 40m Upgrading, REFL11 Noise Vs Photocurrent 
    Reply  Thu Apr 8 20:53:13 2010, Koji, Update, 40m Upgrading, REFL11 Noise Vs Photocurrent 
       Reply  Fri Apr 9 06:45:28 2010, Alberto, Update, 40m Upgrading, REFL11 Noise Vs Photocurrent 
          Reply  Mon Apr 12 17:09:30 2010, Alberto, Update, 40m Upgrading, REFL11 Noise Vs Photocurrent 2010-04-09_REFL11NoiseMeasurements.png
             Reply  Mon Apr 12 22:44:30 2010, Koji, Update, 40m Upgrading, REFL11 Noise Vs Photocurrent 
Message ID: 2790     Entry time: Mon Apr 12 17:09:30 2010     In reply to: 2785     Reply to this: 2795
Author: Alberto 
Type: Update 
Category: 40m Upgrading 
Subject: REFL11 Noise Vs Photocurrent 

Quote:

Quote:
 

 1) True. My bad. In my elog entry (but not in my fit code) I forgot the impedance Z= 750Ohm (as in the fit) of the resonant circuit in front of the square root: Vn = Vdn + Z * sqrt( 2 e Idc )

2) That is exactly the point I was raising! The measured dark noise at resonance is 2x what I expect.

3) I don't have uncertainties for the fit offset (that is, for the Dark Noise). The quick fit that I used (Matlab's Non Linear Least Squares method) doesn't provide 95% confidence bounds when I constrain the offset parameter the way I did (I forced it to be strictly positive).
Sure. It's not a very good fit. I just wanted to see how the data was going.

I also admitted that the data points were few, especially around the 3dB point.

Today I'm going to repeat the measurement with a new setup that lets me tune the light intensity more finely.

 Here's another measurement of the noise of the REFL11 PD.

This time I made the fit constraining the Dark Noise. I realized that it didn't make much sense leaving it as a free coefficient: the dark noise is what it is.

2010-04-09_REFL11NoiseMeasurements.png

Result: the transimpedance of REFL11at 11 MHz is about 4000 Ohm.

Note:
This time, more properly, I refer to the transimpedance as the ratio between Vout @11Mhz / Photocurrent. In past entries I improperly called transimpedance the impedance of the circuit which resonates with the photodiode.
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