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Entry  Mon Feb 23 14:57:23 2015, Zach, Laser, M2 ISS, 3-mm diode initial noise measurement 3mm_diode_noise_5V.png
    Reply  Mon Feb 23 17:57:49 2015, rana, Laser, M2 ISS, 3-mm diode initial noise measurement 
       Reply  Mon Feb 23 19:55:08 2015, Koji, Laser, M2 ISS, 3-mm diode initial noise measurement 
       Reply  Thu Feb 26 18:47:59 2015, Zach, Laser, M2 ISS, 3-mm diode dark current and noise 7845_turnon.PNG7843_turnon.PNG3mm_pd_noise_5V_2_25_25.png
Message ID: 1207     Entry time: Mon Feb 23 14:57:23 2015     Reply to this: 1208
Author: Zach 
Type: Laser 
Category: M2 ISS 
Subject: 3-mm diode initial noise measurement 

I was preparing to do an initial test of the M2 ISS readout board with the 3-mm diodes on the SiFi test setup when I noticed some anomalously high noise on one of the diodes. So, I decided to make a more careful measurement and test all 4 diodes. I found that only one (S/N 7845) exhibits this very bad excess 1/f noise, but all four have it present at some level.

For this test, I had the transimpedance fairly high at Z = 2.7 k\Omega since I am only working with < 5 mW of power, and the diodes were completely blocked for this measurement and put in a dark box. The bias was 10 V at first, but then reduced to 5 V in an attempt to reduce the excess noise after I read on the datasheet that 10 V was an absolute maximum for some reason. I did not record the difference in noise from 10 V to 5 V, but this is a test I will likely try (though perhaps not up to 10 V anymore).

While 7845 is clearly bad, the others are probably OK for now; they are not acceptable for low-power/high-Z operation, but are likely just fine for our high-power testing since we will expect shot noise levels of >100 pA/rtHz, with SNR with respect to PD noise increasing as \sqrt{P}.

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