Checking the amplifier power, posted by Ronic Chiche at ThomX igloo about lasers and optics | detectors and electronics
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we did a long term run (25 mn) with the powermeter located at the FPC position at 33% amplifier ratio.
the initial power was 18W .
then, it goes to 18.5W in 10 minutes, then 5 minutes later, it goes to 18.3W and stay stable until the end the run. |
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Checking the amplifier power, posted by Ronic Chiche at ThomX igloo about lasers and optics | detectors and electronics
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I put back and aligned the 1/2 waveplate only and I get 71kW max after its optimization and optimizing the CEP and alignment (without walking procedure).
this waveplate change a lot the reflected power seen on the CH2 of the scope.
to be continued this afternoon... |
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Checking the amplifier power, posted by Ronic Chiche at ThomX igloo about lasers and optics | detectors and electronics
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this afternoon, we put back the 1/4 and 1/2 waveplates and after a long alignment/angle tuning/CEP optimization process, we hardly got 80-81kW in the
cavity for 33% amplifier ratio. the transmission photodiode is then ~ 7.5 divisions (500mV/division) on the scope.
BUT during the 1/2 and 1/4 waveplate angle tuning process, we clearly saw: |
Electrons-Photons phase stability measurement, posted by Ronic Chiche at ThomX igloo about lasers and optics | detectors and electronics 
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we installed a measurement at the IP with the BPM for ion cleaning for electrons and we used a fast photodiode at the output of the FP-cavity and measured
with a fast oscilloscope the phase jitter between the 2 signals.
in red, the BPM signal |
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Electrons-Photons phase stability measurement, posted by Ronic Chiche at ThomX igloo about lasers and optics | detectors and electronics
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the phase between the 500Mhz ring RF oscillator and the electrons is measured on a BPM and is very stable after 2-3ms (<< 6ps, typically) !
in the same time, we can use the residual phase beating after our 500MHz mixer to estimate the phase noise coming from the laser part.
the rms noise of this signal is around 60mV for 1.25V peak (2.5 pk-pk) signal => ~ 50mrad rms |
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optical attenuator added on the diffuser + new PID parameters, posted by Ronic Chiche at ThomX igloo about lasers and optics | detectors and electronics
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Today we did several long runs (~1h each) at ~23kW, 46kW, 66kW with different PID parameters which seems better.
P = 0.1
I = 0.0015 |
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New recipies with additionnal attenuation before the diffuser, posted by Ronic Chiche at ThomX igloo about lasers and optics | detectors and electronics
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With optical attenuation only
For ~ 92kW power in the FP-cavity:
Alplhanov amplifier ratio : 33% |
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long run to test the appearance of high frequency noise, posted by Ronic Chiche at ThomX igloo about lasers and optics | detectors and electronics
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Today with Daniele, we did 6 long runs at different power (23kW, 46kW, 66kW, 73kW, 92kW, 92kW)
All the lock loss in between these several runs are due to FPC locking parameters change.
most of the few lock losses during the stable power duration, are due to 20Hz oscillation noise or because we forgot to center properly the PZT |
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long run to test the appearance of high frequency noise, posted by Ronic Chiche at ThomX igloo about lasers and optics | detectors and electronics
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today, long run directly at full power (33% amplifier ratio) => 98kW in the FPC at the very begining of the run.
(P=0.05 / I=0.0005 / D=0.6)
10-40 min : almost misalignment effect (CEP did not change so much) |
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New recipies with additionnal attenuation before the diffuser and new x3 amplifier on laser PZT, posted by Ronic Chiche at ThomX igloo about lasers and optics | detectors and electronics
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With optical attenuation + x3 amplifier on laser PZT channel + feedback tuning
Temporary recipie for ~ 92kW power in the FP-cavity:
(in the previous scheme, without x3 laser PZT amp, a good lock was achieved for a PDH signal power noise ~ 70 mV rms) |
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Tuning of the slow feeback loop analog BW + fast feedback loop gain + PID, posted by Ronic Chiche at ThomX igloo about lasers and optics | detectors and electronics
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Today with Daniele, we tuned the potentiometer after the Laselock which drives the analog BW of the PID on the laser PZT,
and we tuned also the fast loop gain (with the rotary potentiometer dedicated to it) => the PID parameters have changed.
so, the recipies has changed => to be updated |
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Alignment correction during the summer break, posted by Ronic Chiche at ThomX igloo about lasers and optics | detectors and electronics
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I restarted the FPC system this morning.
after some classic alignement procedure (some LEFT steps on the cavity injection motors X & Y) and CEP tuning,
I got 92kW for 33% amplifier ratio. |
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polarization measurement of the FP cavity beam, posted by Ronic Chiche at ThomX igloo about lasers and optics | detectors and electronics
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today, with Daniele, we did a simple polarization measurement in transmission of the FP cavity beam.
1) we locked the FP cavity and measured 82.5kw (for 33% amplifier ratio) with the power-meter moved a little bit further (this is maybe the reason
why the power is a little bit lower than usually measured). |
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High frequency noise, posted by Ronic Chiche at ThomX igloo about lasers and optics | detectors and electronics
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Today, the lock of the FPC was particularly bad (maybe the worst ever seen), with a lot of high frequency noise.
the lock was impossible during several minutes !
we tried to switch off all the equipments of the machine, one by one without any effect on the lock. |
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High frequency noise, posted by Ronic Chiche at ThomX igloo about lasers and optics | detectors and electronics
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At the end of the day, we found out what was the origin of this noise : some road renovation work with jackhammer and road roller just at the entrance
of the "Igloo".
this origin was 100% correlated with a large increase of the accelerometer signal. |
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High frequency noise, posted by Ronic Chiche at ThomX igloo about lasers and optics | detectors and electronics
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After this observation, we did a test with Daniele to try to correlate the road traffic in front of the Igloo with the lock losses observed on the FPC.
We didn't see any clear correlation. Cars or buses are not the direct origin of the FPC lock losses... only when some heavy load is hitting
the building, we observed a clear correlation. |
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High frequency noise, posted by Ronic Chiche at ThomX igloo about lasers and optics | detectors and electronics
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we did some tests with Marie to make some vibrations on the door.
below, I exhibit some pictures of the scope with the accelerometer plugged on it without or with noise...
this level of noise is not able to make the FPC loosing the lock. |
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Noise issue, posted by Ronic Chiche at ThomX igloo about lasers and optics | detectors and electronics
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since several days, we see that the locking is more and more unstable and the lock duration was sometime less than 20-30 seconds !
1) I tried to optimize the feedback loops
I discovered that the gain on the fast loop on the laser EOM was very low and was almost uneffective for the global stability of the lock (I |
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Noise issue, posted by Ronic Chiche at ThomX igloo about lasers and optics | detectors and electronics
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yesterday, in the same conditions, we had so many locking issues... exactly in the same way than before. :-(
so we still have "locking issues" depending on something we didn't find...
today, we removed the "1/2 voltage divider" before the PZT amplifier to get back the full dynamic. |
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High frequency noise, posted by Ronic Chiche at ThomX igloo about lasers and optics | detectors and electronics
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This morning, I installed a high-voltage probe (1:1000) on the AC-line to see if one could detect a correlation between lock losses and AC-line voltage
variations.
I observed many lock losses but without any variation or correlation of the AC-line signal (scope set in "peak detect" with "envelope" |