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==Daily Log==
'''12/3/14'''
Been swamped with classwork lately, but a few lab things worth noting.
I've pretty much concluded the 2 photon experiment can't be done with the current setup. The way Josh did it previously was by broadening the cavity peaks and then tuning the frequency differences with the laser piezos. He could then scroll to a different broadened peak, which would be about 200 MHz away. We're at higher pressure and locking makes the frequency jump a lot and in a pretty unpredictable way.
I think we need to pre-stabilize the lasers with a low finesse cavity. This will 1). make locking to the high finesse cavity much easier. The lasers would potentially stay locked for a lot longer so that we could just focus on tuning them rather than keeping them locked. And 2). Give us another way to tune the laser frequency--we could lock to different peaks of the low finesse cavity to change frequencies by its free-spectral range.
Another way we could maybe do the experiment would be if we could recreate the peak broadening behavior. We used to turn off the slow feedback box and ramp the cavity or laser piezo. When the piezo hit the resonance position, the fast feedback would keep it resonant for a bit (even as the piezo kept moving), resulting in a broadened cavity peak. This doesn't work with the vescent box even when we unplug the piezo, which I think is because the minimum frequency the the current driver responds to is different from our previous setup. I'm waiting to hear back from vescent about this issue. In the mean time I tried making a high-pass filter so that I could manually adjust it (well, I couldn't decrease the minimum frequency, but I could effectively increase it though). I wanted it to be able to filter out frequencies below a couple hundred Hz, but it didn't really do anything though, which might be partly because I used a pot with wire coils which probably has a big impedance, but from talking to people it also sounds like you need to use an active filter at low frequencies. I probably should just buy something then, but I'll wait until I'm more convinced that will help.
The manometer also seems like it got calibrated somehow, since it was saying the cavity was pumping down to about 20 times lower pressures than it usually does and that seems unlikely. I unplugged it and reconnected it, and it gave more normal values, but it's a little bit offset from where it used to be, probably by 10-20 mV. That shouldn't really matter since most of the pressures we're at are in tenths of volts and I can't really get those accurate to 10 mV anyway.
There was also an issue with the 1064 laser giving unstable wavelength readings. Like fluctuations of about 500 MHz every second (I mean, it stayed withing about 1 GHz over pretty long times, but just bounced around within that). This turned out to be because of the multimode fiber we were using. The frequency wasn't actually doing this, but the fiber was supporting extra spacial modes which was confusing the wave meter. Using a single mode fiber gives readings stable to 10s of MHz, which makes more sense. I couldn't get enough of both 1064 and 155 coupled with a single mode fiber, so I might need to order one that will work better, or just keep in mind the deal with the 1064 one.
'''11/19/14'''
Once again, 1555 locked at 0.05 atm with minimal adjustment. This is a very good sign. I've got a new procedure for getting 633 back if the 780 gets misaligned. No cameras or IR viewers required and it's quicker and easier--put a fair amount of gas in (maybe 1 V or so) so that there aren't many spacial modes without 633 and there's a lot of it if alignment is good. On the 1064 side of the cavity, turn down the power and use a card to overlap the 1064 and 780. Then turn the power back up, lock the 1064, and on the 780 side of the cavity use the other alignment mirror to overlap the transmitted 1064 with the 780. Repeating this 2-3 times will get 633 back depending on how badly aligned it was. Optimal alignment will change slightly when you switch back to whatever pressure you were working at, but it should still easily be detectable and so is not hard to fix.
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