Removing high order modes, posted by Ronic Chiche at ThomX igloo about mechanics | lasers and optics | detectors and electronics 
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here is the picture of the L-shape arm and the inside of the vessel.
this image corresponds to the "zero" position on each positionner.
Ronic |
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33MHz oscillator + Alphanov amplifier lock, posted by Ronic Chiche at ThomX igloo about lasers and optics
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redoing the PDH error signal scheme with discrete components is more flexible and it is easier to check the signal/noise ratio.
now, we are able to get a quite clean lock only with the PZT correction (w/o fast feedback correction using the EOM) even with both motors controllers
ON (cavity and laser). |
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Removing high order modes, posted by Ronic Chiche at ThomX igloo about mechanics | lasers and optics | detectors and electronics
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yesterday with Daniele, we tried again to move the arm horizontally and vertically from the "zero position" to have a better understanding
of the beahvior,
but it is roughly the same : |
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work with HV voltage on the Laselock, posted by Ronic Chiche at ThomX igloo about lasers and optics | detectors and electronics
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This afternoon, I connected the HV output of the Laselock (instead of the standard 0-10V output) to the FP-cavity PZT to increase the locking range.
I didn't see any degradation of the FP-cavity/synthesizer lock.
Ronic |
20Hz oscillation in the locking between Laser and FP-cavity, posted by Ronic Chiche at ThomX igloo about mechanics | lasers and optics | detectors and electronics
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this morning, we tried to find the origin of the 20Hz oscillation.
- we switched OFF the laser Smaract motors controller => no change
- then, we addionally disconnected the FP-cavity PZT cable from the Laselock (we put a charge of 1kohm) => no change |
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20Hz oscillation in the locking between Laser and FP-cavity, posted by Ronic Chiche at ThomX igloo about mechanics | lasers and optics | detectors and electronics
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this afternoon, we did 2 tests to better understand this 20Hz oscillation:
- we locked the amplified laser directly to the 500MHz ring reference oscillator, without any intermediate locking to the FP-cavity => no
change |
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Fast feedback loop between laser and FP cavity, posted by Ronic Chiche at ThomX igloo about lasers and optics | detectors and electronics
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this afternoon, we tried to better understand how to drive properly the EOM to kill high frequency noise.
we locked to laser on the FP-cavity as usual.
then we injected a 0-10V square signal on the laser EOM @ 1KHz (with fast rise and fall times ~ 10ns) |
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!!! strange FP cavity behavior => impossible to lock !!!, posted by Ronic Chiche at ThomX igloo about mechanics | lasers and optics | detectors and electronics
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suddenly, BEFORE switching the HV amplifier ON and BEFORE connecting it to the EOM (in order to explore the HV effect on the EOM for the fast feedback
loop),
we lost the lock between the laser and the FP-cavity: in attchement a plot a the lock with the "best" PID parameters. |
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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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!!! strange FP cavity behavior => impossible to lock !!!, posted by Ronic Chiche at ThomX igloo about mechanics | lasers and optics | detectors and electronics
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this morning, we tried:
- to move a bit the arm of the L-shape off the beam axis (in case of it could have touch something and induce vibrations) => no effect
- to change the CEP to get an equivalent lower Finesse => weak improvement |
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!!! strange FP cavity behavior => impossible to lock !!!, posted by Ronic Chiche at ThomX igloo about mechanics | lasers and optics | detectors and electronics
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it could be also an optical unstability, as when the intra-cavity power increases, the radius of curvatures of the mirrors increases too due to thermal
effect, and then one could go in the instability region.
but if it was the case, by reducing the power in the FP-cavity, we would also reduce the thermal effect and then, we would come back in the stability |
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!!! strange FP cavity behavior => impossible to lock !!!, posted by Ronic Chiche at ThomX igloo about mechanics | lasers and optics | detectors and electronics
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This morning,
- I installed the fast feedback loop.
now, the error signal goes to the Laselock AND |
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!!! strange FP cavity behavior => impossible to lock !!!, posted by Ronic Chiche at ThomX igloo about mechanics | lasers and optics | detectors and electronics
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this afternoon, in adjusting the CEP and improving the parameters of the lock, I was able to get ~ 47kW stable inside the cavity, always for 30% of laser
amplification ratio.
it confirms that the Finesse, and then the gain of FP-cavity, has suddenly increased thanks to some "mirrors surface cleaning" |
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Fast feedback loop between laser and FP cavity, posted by Ronic Chiche at ThomX igloo about lasers and optics | detectors and electronics
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I copy the post about Fast Feedback loop : https://elog.lal.in2p3.fr/FPC/THOMX+commissioning/265
This morning,
- I installed the fast feedback loop. |
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!!! strange amplifier beam pointing fluctuations !!!, posted by Ronic Chiche at ThomX igloo about mechanics | lasers and optics
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this morning, I locked the cavity to ~25kW without any problem.
but this afternoon, the reflected power exhibited low frequency (~1Hz) fluctuations of about 10% without any lock.
the reflected PhD is a DET10 which has a small surface. |
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Tests of pointing stability of the laser CFP, posted by Daniele Nutarelli at ThomX igloo about lasers and optics
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Last monday with Victor we have cheked the stability of de pointing of the laser FP.
The climatisation was operating since 3 days in satble way. The laser pointing was very stable before to inejct in to the cavity (picture 1)
and also for the reflexion from the cavity (picture 2). |
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Strecher and fiber injection alignment, posted by Ronic Chiche at ThomX igloo about lasers and optics
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Today, the power measured at the input of the amplifier (PD_IN on the LAL amplifier software) is 2.5mW instead of >3mW generally measured
The power coming from the NKT/Onefive Origami oscillator is still >37mW (measured directly with the powermeter at the laser output without
OD2). |
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!!! strange amplifier beam pointing fluctuations !!!, posted by Ronic Chiche at ThomX igloo about mechanics | lasers and optics
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we confirmed the effect of the bunker temperature on the laser amplifier "beam pointing" fluctuations.
once the temperature is getting back to stable values, it doesn't happend again.
we bought a temperature data logguer to monitor them in the future: https://www.picotech.com/data-logger/tc-08/thermocouple-data-logger |
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some changes in the feedback scheme, posted by Ronic Chiche at ThomX igloo about lasers and optics | detectors and electronics
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from several weeks, the maximum power stored in the FP-cavity was ~ 5kW.
today with Daniele, we finished to investigate the problem, and now the power inside the FP-cavity is back
to ~50kW for 30% of laser amplifier ratio (~16W). |
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Ring frequency / Laser "day by day" locking, posted by Ronic Chiche at ThomX igloo about mechanics | lasers and optics | detectors and electronics
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| today, the equivalent Smaract position corresponding to the 500.25MHz ring frequency is +156µm on MCS-1/ch0 (closed loop mode) |