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David Notebook: Difference between revisions
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Lock-In: signal input (using only built in amplifier)-- I (10^8), time constant-- 1 sec, slope/oct-- 12 dB, sensitivity-- 50 μV, reserve-- low noise, filters-- off
Checked the power output on the TA and found it was only about 300 mW. Re-aligned the seed laser and the power is back to 1 W. This increased the locking signal, which comes to about 60 pW as measured the detector. Since the chopper is blocking the beam 50% of the time though, the effective power is 120 pW. There are other significant losses from optical elements as well--about 40% of the incident light on the grating goes into the first order at 633 nm (as measured with the HeNe), 93% for the 633 bandpass filter (measured with HeNe), 60% and 70% for the cavity window and mirror, 90% for the dichroic, and 3 silver mirrors and the cavity pickoff at 95% each. All together, this means that we are only getting 5.7% power at the photodiode, including the 50% reduction from the chopper. So inside the cavity there should be about 1 nW of 633.
I turned down the current to the TA, reducing it's power by a factor of 3. This reduced the measured locking signal by a factor of 5, which is not linear but at least the measured power correlates with the 780.
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