enter Thu Dec 10 10:04:54 2020
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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.
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Hm, hadn't tried the phasemeter application. I'll check it out now... if I understand your second comment, you're saying because
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 |