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 Mon Nov 30 11:28:30 2020, aaron, Noise Hunting, Laser, pll Tue Dec 1 10:59:49 2020, aaron, Noise Hunting, Laser, pll Wed Dec 2 13:37:55 2020, aaron, Noise Hunting, Laser, W laser oscillating Thu Dec 3 10:18:07 2020, aaron, Noise Hunting, Laser, pll Thu Dec 3 11:57:52 2020, rana, Noise Hunting, Laser, W laser oscillating Fri Dec 4 10:36:18 2020, aaron, Noise Hunting, Laser, pll Sun Dec 6 19:22:10 2020, rana, Noise Hunting, Laser, pll Thu Dec 10 10:05:03 2020, aaron, Noise Hunting, Laser, pll Wed Feb 10 12:39:08 2021, rana, Noise Hunting, Laser, pll Thu Feb 11 09:59:31 2021, aaron, Noise Hunting, Laser, pll Thu Feb 11 17:24:41 2021, rana, Noise Hunting, Laser, pll Mon Feb 15 14:57:25 2021, aaron, Noise Hunting, Laser, pll
Message ID: 2601     Entry time: Thu Dec 10 10:05:03 2020     In reply to: 2600
 Author: aaron Type: Noise Hunting Category: Laser Subject: pll

enter Thu Dec 10 10:04:54 2020

 Quote: Doesn't the phase meter just read out the noise even with no locking? I thought that was going to be the magic. For locking, the mixer readout is in units of phase and the laser current modulation gives a proportional frequency modulation with no frequency wiggles until > 1 MHz. So it should phase lock with no integrator, but I'm not sure if the free running noise will drive it out of the phase lock or not. I wonder if its possible to use the phase meter as an error signal. It would be much easier to lock frequency instead of phase via a mixer.

Hm, hadn't tried the phasemeter application. I'll check it out now... if I understand your second comment, you're saying because

$f = \frac{d\phi}{dt} \\ \implies \int f dt = \Delta \phi$

an error signal proportional to phase is already integrating the frequency error. Makes sense, but does 'easier to lock frequency instead of phase via a mixer' follow, or is that unrelated?

The Moku phasemeter does produce a nice power spectrum. Here it is up to 200 Hz, I'm working with Anchal's ctn-scripts and pymoku to get the higher frequencies.

Still odd that the beat amplitude is so small. Let's check:

 quantity Power of E beam @ 1611 (power meter) Power of W laser @ 1611 (power meter) 1611 DC voltage from E beam 1611 DC voltage from W beam DC voltage gain responsivity @ 1550 (approx) Expected DC voltage due to E beam Expected DC voltage due to W beam value 307.8 uW 65.7 uW -1.55 V -400 mV 10 V/mA 1 A/W -3.08 V -660 mV

Looks like neither beam is producing the expected photocurrent, but because the error is not the same factor for both beams I suspect alignment / beam size. I'm aligning with some apertures to avoid smearing the beam on lenses. Aligning each beam led to more power, but my procedure doesn't simultaneously align both beams.

exit Thu Dec 10 15:11:30 2020

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