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David Notebook: Difference between revisions
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Now I can compare the HeNe power measured by the power meter and the lock-in. The power meter read 199 μW just before the PVC pipe. I then took out the 780 notch filter before the photodiode and had the photodiode output to the lock-in and the lock-in output to an oscilloscope. The oscilloscope read 6.7 V. I had the sensitivity on the lock-in to 1 V, so using the formula from yesterday for offset square waves, the peak-to-peak voltage from the photodiode should be 1.49 V. Checking the photodiode on the oscilloscope confirmed this was accurate to about 5%. Then
<math> P=\frac{V}{(.38 Amps/W) * (10^4 V/Amps)} = 196 \mu W </math>
With the .38 Amps/W as the responsivity of the photodiode and the 100000 V/Amps is the transimpedance gain of the photodiode. The results agree! This is the power with the chopper on, so double it if we want the actual power that could reach the photodiode.
So for square waves generated from chopped 633 nm light hitting the photoiode with minimum voltage 0 and maximum A as read on the oscilloscope, the unchopped power reaching the photodiode is:
<math> P=\frac{A*Sensitivity}{(4.5*0.38 Amps/W) * (10^4 V/Amps)} = 5.85*10^{-5} (A*Sensitivity) </math>
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