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David Notebook: Difference between revisions
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==Daily Log==
'''10/7/14'''
Ordered 2 HeNes from Ebay so we can return the ones we've been borrowing from the optics lab. I've been wondering if maybe the amount of optical feedback isn't right for the 1555 locking circuit. I was able to get kind of a lock with only the first integrator on (20 kHz). Then I adjusted the optical feedback and then the proportional gain. The best performance seemed to be between 2-3 V optical feedback when the circuit isn't locked. It's currently set at 2.5V, which will give some locking with the proportional gain course knob 2 clicks up and the fine gain most of the way up.
'''10/1/14'''
Diode performance seems good on the OSA too. The peak from the threshold test was single mode and stayed single mode when I increased the current up to the operating value. When trying to set up the locking circuit, it would only occasionally go multi-mode and would quickly return to single mode when I turned down the amount of feedback (previously this would generally require re-scanning with the grating). I never had to touch the grating after the initial threshold test. By the end of the day, I had it locking using just the proportional gain and the first integrator on the Vescent box. The lock would quickly start falling but jump up again before disappearing entirely. This sustained for ~1 min, which is better than I've ever seen. The transmitted power was ~100 mW, which I think is lower than we had previously, but I'll have to look through Josh's notes. I think this will get better when I work with the optical feedback and the other integrator and differentiator. It was so much easier trying to improve the lock since the laser would stay single mode. Much more power is getting to the fiber amplifier too so it never shut off due to low power.
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