40m QIL Cryo_Lab CTN SUS_Lab TCS_Lab OMC_Lab CRIME_Lab FEA ENG_Labs OptContFac Mariner WBEEShop
  40m Log  Not logged in ELOG logo
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: 2795     Entry time: Mon Apr 12 22:44:30 2010     In reply to: 2790
Author: Koji 
Type: Update 
Category: 40m Upgrading 
Subject: REFL11 Noise Vs Photocurrent 

Data looks perfect ... but the fitting was wrong.

Vn = Vdn + Z * sqrt( 2 e Idc ) ==> WRONG!!!

Dark noise and shot noise are not correlated. You need to take a quadratic sum!!!

Vn^2 = Vdn^2 + Z^2 *(2 e Idc)

And I was confused whether you need 2 in the sqrt, or not. Can you explain it?
Note that you are looking at the raw RF output of the PD and not using the demodulated output... 

Also you should be able to fit Vdn. You should put your dark noise measurement at 10nA or 100nA and then make the fitting.

Quote:

 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.

 

ELOG V3.1.3-