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David Notebook: Difference between revisions
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==Daily Log==
'''6/9/14'''
We realized just before DAMOP that we were getting feedback to the 780 laser. A lot of it seems to be coming from the cavity mirror, since the frequency/mode of the 780 seed changes when adjusting the cavity piezo. We're going to retune the isolators and add in a second one before the seed.
'''DAMOP 20-14!!!!!'''
'''5/23/14'''
The last few days were spent trying to improve the 633 signal and better isolate it. We used a [[Thorlabs PDA36A Si Switchable Gain Detector|Thorlabs PDA36A]] photodiode and pushed it right up against the fiber, but could only get a very weak signal. However it did seem to correspond with locking the laser. The laser locked well enough to try walking the fiber connection and the signal was improved, but eventually it was discovered that the 780 beam was blocked at the source. This means that some other light was getting to the fiber, even past all of the filters we had set up. 1064 seems a likely candidate. We added in an old cavity window, which reflects almost all 1064, realigned the 780 beam and found a signal we believe comes at least mostly from 633. We also switched to the much more sensitive [[UDT Sensors PIN 5DP Photodiode|PIN 5DP Photodiode]] and [[Stanford Research Systems SR570 Low Noise Current Preamplifier|SR570 Preamplifier]] combination. While the previous signal was responsive mostly to adjusting the fiber coupling and showed little response to the 780 beam alignment, this signal was responsive to both. We were able to improve the signal by adjusting both the fiber coupling and 780 alignment. We also tried using a power meter, and while the results were not entirely clear, we believe we might have seen a signal of a few tenths of nW when locking.
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