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==Daily Log==
'''10/15/14'''
I tried to follow the various signals through all parts of the PDH circuit. I made slight adjustments here and there, and most notably added some BNC length to change the phase delay on the local oscillator. I also turned off the integrator on the lock-box and so was just using the proportional gain. The error signal should be linear near resonance, so do we even need differential and integral adjustments? I saw the best performance yet, with powers over 300 mW and fairly consistent.
I also saw a lot of weird behavior today. Ramping was very inconsistent, and it was hard to see if the laser was aligned even when I knew it was close and I should see some peaks. The oscilloscope near the cavity would show very little or no signal and sometimes the other one would show much more. It seemed more than just scaling, but a difference in signal to noise ratio. They are getting the same signal that is just split and the oscilloscope settings were comparable. I also didn't see the changed in error signal I would have expected when adjusting the phase delay length by half a wavelength (~1.9 m) (see the figure on page 32 of Green's thesis--everything looked like the pi/2 and 3*pi/2 plots, no matter how much cable I changed). I'm also still seeing noise on the error signal and DC offset channels. It seems different everyday. It's only present when the RF is on, but today there was a lot in the 20 Hz region (yes, Hz) on the DC offset channel. I still don't know what the cause might be and if it's a problem.
The weirdest thing by far was the current driver starting oscillating somewhat again, by maybe 1-2 mA. It's don't think it's bad temperature tuning again, because the temperature was staying within tenths of mK to the setpoint and I adjusted the setpoint too in case there were any weird resonances. I wanted to repeat the threshold test, and I couldn't turn the current down below 100 mA. At the lowest setting, that was what it output. Turning it off and on and unplugging the servo connection eventually got it lower, but then it would just start creeping back up without me adjusting anything. I checked with a power meter and the laser powers were consistent with the current value that was displayed.
'''10/9/14'''
I tried to track down where the noise was coming from. The DC error output on the vescent box only is noisy when it's connected to the error signal and the RF is on (doesn't matter whether the laser is on and there is actually an error signal). The full height is about 15 mV of noise. I checked the laser diode output using a photodiode and the noise doesn't seem to be coming from there. Most likely seems the RF amplifier in the circuit, although the low pass filter isn't cutting this as much as I'd think either. I tested the amplifier by itself though and it didn't show any sidebands, which would have been the obvious cause. It does have signals at integer multiples of the input RF signal, but those are all around 10 db lower. I checked the same amplifier on the 1064 setup and it showed similar behavior. The vescent box on the 1064 also shows similar noise with, although slightly less, so maybe nothing is broken and this has always been there.
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