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David Notebook: Difference between revisions
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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.
Vescent also put an updated manual for the servo controller up, and it has some helpful info. There are apparently some secret switches you can only get to by taking the side panel off, a few of which do interesting things. One secret switch lets you set the box to ramp in "master" mode rather than "slave". Previously we had to input an external ramp, which we could then turn on or off and adjust the amplitude of. There's nothing really wrong with this that I can see, but it's just another piece of equipment and nest of wires to complicate things. I switched to the internal ramp, but I might need to change back if we ever get the peak broadening working again, since you can't ramp while locking with just the vescent box. There's also a switch to change it so that the vescent box will only output a positive ramp. This is good since we don't want to put a negative voltage to the piezo. We normally have to manually put an offset on it each time and then take it off at the end of the day (since we don't want to leave a voltage on the piezo). This also means there's not really a reason to output to the Thorlabs piezo controller. All it basically does is serve as a buffer to prevent negative voltage going to the piezo, amplifies the signal, and lets you make small adjustments. The internal ramp seems strong enough, so I've switched to just using that for now. I'm not sure if it's better that way, but I'm hoping maybe it will make the lock better since it kind of has more direct control over the piezo now without having to go through another device with it's own gain and phase delay.
'''11/19/14'''
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