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Yes it did.
For long time, the crystal temperature C1:PSL-126MOPA_LTMP was 43~46deg. Now it is 34deg. Try ~10deg lower temperature.
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I wonder if the all the tinkering on the PSL laser done recently to revive the power have changed the PSL NPRO temperature and so its frequency. That could also explain why the beat doesn't show up at the same temperature of the NPRO as I used to operate it. Although I scanned the NPRO temperature +/- 2 deg and didn't see the beat.
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Beat found at 30MHz with auxiliary NPRO temperature of 37.19 degrees, vs. ~48 deg as it used to be.
The beat is small (-70dBm). PLL alignment has to be improved.
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PLL alignment improved. Beat amplitude = -10dBm. Good enough.
DC readouts at the PLL photodiode:
V_NPRO = -4.44V
V_PSL = -3.76V
The NPRO beam is attenuated by a N.D.=1 attenuator just before going to the photodiode.
Something strange happened at the last. Right before -10dBm, the amplitude of the beat was about -33dBm. Then I was checking the two interfering beams with the IR card and saw that they overlapped quite well. I then turned my head back to the spectrum analyzer and suddenly the beat was at -10dBm. Not only, but a bunch of new peaks had appeared on the spectrum. Either I inadvertently hit the PD moving it to a better position or something else happened.
Like if someone was making some other modulation on the beam or the modulation depth of the PSL's sidebands had gone up. |