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David Notebook: Difference between revisions
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Spent the last 2 days setting up the beam chopper and a lock-in amplifier for it. It works very well and after sending the HeNe through 2 irises I could easily measure it 1 nW. I thought I was seeing a signal at one point that only appeared when locking when the 780 was one, but I haven't been able to replicate it yet. It's difficult to optimize the settings on the amplifier since I can only lock the 1064 for a second or two at a time. Is there some way I can do it while ramping instead?
'''11:43 am''' I see something! I'm almost positive. Is champagne allowed in lab? What time does happy hour start at the library? When locking the 1064 beam with the 780 on, there is a noticeable jump in signal that is not present with the 780 off. Turning on/off the 780 changes the DC offset of the signal, but the jump when locking is about 10 times higher when 780 is on. The signal is clearly correlated with the lock.
Settings are as follows:
Gas Pressure: 2.515 volts
633 bandpass filter is in place before the diffraction grating
Oscilloscope scale is 20 mV (signal when locking jumps ~100 mV)
Chopper frequency: 500 Hz (chopper is outputing the frequency to the lock in--one of several variations I've tried including using the lock-in to set the chopper frequency and using a function generator to set both frequencies. Having the chopper in charge seems to be the most stable).
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
Things to try this afternoon--remove photodiode and make sure 633 flashing is visible with current alignment, remove 633 filter--offset should change, but locking signal shouldn't change much (check how much 633 it should pass), move 633 filter to the front of the detector--does this reduce DC offset when turning 780 on/off?, turn down 780 power--does locking signal decrease linearly?
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