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David Notebook: Difference between revisions
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Jared and I have both thought that the visible power meter head has been giving somewhat high values (10% or so), so I'm skeptical of it's readings. However, further investigation of the lock-in reveals it is supposed to always multiplies the output by an additional 10V, regardless of the settings. Page 21 of the manual alludes to this, but I couldn't find a full description. I measured this value as closer to 9 though--I used a function generator to send in a square wave at 500 Hz with a max amplitude of 2V and a min of 0V, similar to the type of signal the photodiode should send in. With the gain setting on the lock-in as "1V" or "1μA", the output was 9V. A 100 mV average value square wave gave 0.9V.
Ok, the multiplicative factor of 9 is checking out more--it matters for the lock-in whether the input signal is a sine wave or square wave. For a sine wave, it singles out anything oscillating at the set frequency and gives the RMS voltage. For a square wave, it takes only the first fourier component (4/π sin(ωt)) and then the RMS value (multiplied by <math> 1/ \sqrt{2} </math>). Page 31 in the manual is helpful. So for a square wave pulsed laser at 500 Hz like I'm sending in, the output voltage should be <math> \frac{0.5*peak
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