lock oscillateur 33MHz - synthé 500MHz, posted by Ronic Chiche at Optical room about detectors and electronics
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this afternoon, we were able to lock the laser on the FP-cavity and the FP-cavity on the Ring reference oscillator in a same time from the control room.
the procedure when laser, cavity and reference oscillators are far in frequency, is :
1) start the amplifier to get the laser signal in the reference photodiode used to measure the 33MHz. |
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lock oscillateur 33MHz - synthé 500MHz, posted by Ronic Chiche at Optical room about detectors and electronics
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after a sudden FP-cavity Finesse increase, we had to install the Fast Feedback Loop in order to continue to lock the cavity.
this afternoon, I was able to lock both the FP-cavity and the Laser on the 500.25MHz oscillator reference.
I had to change the CEP to reduce the effective Finesse and help to get a better stabililty => P ~ 25kW inside the FP-cavity for 30% of laser |
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lock oscillateur 33MHz - synthé 500MHz, posted by Ronic Chiche at Optical room about detectors and electronics
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This morning with Daniele, we changed the laser/RF locking scheme :
1) we use the laser 33MHz internal photodiode to do some beating with the 33MHz RF generator (A Rigol generator locked on the 500MHz Ring oscillator).
this beating is only for monitoring purpose, in order to manually adjust the laser frequency at the beginning of a run. |
laser operation again with machine OFF, posted by Ronic Chiche at ThomX igloo about lasers and optics
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The laser start at 33% with 92 KW optimized and
P=0.03
I=0.0005 |
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laser PZT amplifier, posted by Ronic Chiche at ThomX igloo about detectors and electronics
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this afternoon, I added the Gain = 2.8 amplifier at the output of the Laselock to drive the laser PZT.
the power supply of the board is disymetric to address the correct maximal dynamic range of the amplifier (~ 30V) and voltage drop (~ 2V) related
to the power supply voltage. |
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fixing CVBG issue, posted by Ronic Chiche at ThomX igloo about lasers and optics | detectors and electronics
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the CVBG of the compressor module seems to have an issue.
here is the plan of the work :
1) faire des résonances avec la CFP |
fixing CVBG issue, posted by Ronic Chiche at ThomX igloo about lasers and optics | detectors and electronics 12x
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1) this morning, I aligned to CFP to get back 82kW in the cavity for 33% of amplifier ratio.
thus, we can ajust the iris positions on the optical table to fix the CFP optical path before touching the CVBG.
2) we aligned the 5 iris. all of them were misaligned by 1-2mm, principaly vertically (maybe because we had to change the CFP frequency some |
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fixing CVBG issue, posted by Ronic Chiche at ThomX igloo about lasers and optics | detectors and electronics
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this morning with Daniele, we realigned the amplifier beam axis on the iris position.
it was pretty fast an easy => we got rapidely some resonance and we locked back to 87kW @33% amp ratio after tuning CEP and alignment.
we tried to play on the L-shape but we didn't a clear effect. |
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elliptic mode shape, posted by Ronic Chiche at Optical room about lasers and optics
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the mode shape @ 5-15kW is very elliptic (50% of ellipticity : large size = 2x small size).
we only changed M1 and did not move M2,M3,M4.
what are the possible reasons for the ellipticity: |
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drift calculation for the SMA100A, posted by Ronic Chiche at ThomX igloo about lasers and optics
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the goal is to estimate what could be the frequency drift at 500MHz for the SMA100A: see phase noise datasheet in attachement
Sphi(f) = FFT ( Rphi(T) ) = FFT ( < Phi(t) Phi(t+T) > )
at low frequency, Sphi(f) ~ A / (f^n) = A*(2pi)^n / (i2pi*f)^n => Rphi(T) = A*(2pi)^n*T^(n-1) / (n-1)! |
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day by day run for X-ray production, posted by Ronic Chiche at ThomX igloo about mechanics | lasers and optics | detectors and electronics
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the RF frequency changed from 500.1003MHz to 500.0913MHz => it reduced by 9kHz @ 500MHz which is equivalent to 600Hz @ 33MHz (we measured 500Hz @
33MHz). the electron orbit length increased, so we have to increase the cavities length => increase motor values by ~ 68µm.
for the laser cavity : 1.496 560 mm => 1.564 560 mm |
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day by day run for X-ray production, posted by Ronic Chiche at ThomX igloo about mechanics | lasers and optics | detectors and electronics
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at the begining of the day, we started to get ~81kW in the FPC for 33% amplifier ratio and after ~1h, we got 84kW after CEP and alignment tuning.
at the end of the day, we got 89kW without walking alignment.
we tried to improve a bit the robustness of the FPC and RF locks: |
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day by day run for X-ray production, posted by Ronic Chiche at ThomX igloo about mechanics | lasers and optics | detectors and electronics
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today with Alice, we planned to do a long run with ~80kW in the FPC to check if the lock problems are coming from the interaction with the machine or
not.
the goal is to check this assumption on a full day comparable with a day of X-ray production. |
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day by day run for X-ray production, posted by Ronic Chiche at ThomX igloo about mechanics | lasers and optics | detectors and electronics
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we observed that :
- the MOT.03 motor always exhibits some perturbations on the transmitted, reflected and PZT signals (see "peaks" in the picture) in
contrary to the MOT.06 motor. |
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day by day run for X-ray production, posted by Ronic Chiche at ThomX igloo about mechanics | lasers and optics | detectors and electronics
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last thing we tried :
we removed the threshold on the FPC/RF error signal.
=> we cannot choose automatically the RF bucket anymore (we need to manually let the phase drift slowly and start the lock at the right moment). |
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day by day run for X-ray production, posted by Ronic Chiche at ThomX igloo about mechanics | lasers and optics | detectors and electronics
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This morning, I added an amplifier on the 33MHz beating signal in between the mixer+LPF and the scope/Laselock.
it seems to improve the robustness of the RF/FPC lock.
because of this gain, I increased the upper and lower thresholds on the search criterion of the RF/FPC lock from +/-50mV to +250mV/-200mV |
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day by day run for X-ray production, posted by Ronic Chiche at ThomX igloo about mechanics | lasers and optics | detectors and electronics
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major result of the day: X-ray vertical scan by moving the hexapod
abscise : hexapod position
ordinate : xray flux in asynchronous condition |
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day by day run for X-ray production, posted by Ronic Chiche at ThomX igloo about mechanics | lasers and optics | detectors and electronics
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this morning, Kevin reduced the steering current in the IcePap controllers of the FP cavity motors.
the motor MOT.06 was producing a pattern in the Transmission signal when it was moved and doing a lock loss very often.
so, we changed its current from 0.8A to 0.4A and it fixes the problem => no more systematic lock loss. |
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day by day run for X-ray production, posted by Ronic Chiche at ThomX igloo about mechanics | lasers and optics | detectors and electronics
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this morning, I restarted the cavity after the Christmas shutdown.
everything went fine.
I got ~ 86kW for 33% laser amplifier ratio after optimization of the CEP and alignment with walking procedure. |
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day by day run for X-ray production, posted by Ronic Chiche at ThomX igloo about mechanics | lasers and optics | detectors and electronics
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today we did x-rays => we got 41 000 pA at maximum and 90kW in the FPC for 33% amplifier ratio.
finally, I changed the strategy for the feeback on RF.
i removed the integration and derivative parameters and reduced the gain parameter : |