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Entry  Wed Apr 6 19:36:32 2011, Aidan, Summary, Green Locking, (In)sanity check of Green PD - some inconsistencies PD_measurement.pngplot_PD_RF_ratios.pdf
    Reply  Thu Apr 7 16:09:17 2011, Aidan, Summary, Green Locking, (In)sanity check of Green PD - some inconsistencies 
       Reply  Thu Apr 7 19:28:02 2011, Koji, Summary, Green Locking, (In)sanity check of Green PD - some inconsistencies SGD-444A.png
Message ID: 4500     Entry time: Thu Apr 7 16:09:17 2011     In reply to: 4494     Reply to this: 4501
Author: Aidan 
Type: Summary 
Category: Green Locking 
Subject: (In)sanity check of Green PD - some inconsistencies 

I think I had underestimated the responsivity of the Silicon PD at 1064nm. The previous value was based on a rough search online for the responsivity of Silicon (I couldn't find the product number of the actual PD we are using). For instance, the PDA100A Si detector from Thorlabs has a responsivity of 0.35-0.4A/W at 1064nm. 

If we calculate the responsivity of the Hartmut PD from the measurements I made today (input power = 0.300mW, output voltage = 5.56mV, effective transimpedance = 80 Ohms), then the responsivity at 1064nm is 0.23 A/W which is not an unreasonable number given the response of the Thorlabs detector.

Quote:

Measurement Value
Responsivity of Silicon PD at 1064nm 0.02 A/W (estimate)
Responsivity of 1611 New Focus PD at 1064nm ~0.8 A/W
   

There is one other troubling point: using the estimate of responsivity on the Harmut PD * incident power * transimpedance at DC = (0.02A/W) * (0.28mW) * (80 V/A) = 0.45 mV.

But the measured DC voltage is 6.5mV = inconsistent.

 

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