Possible causes for the noise in the FP-cavity system, posted by Ronic Chiche at ThomX igloo about mechanics | lasers and optics | vacuum | detectors and electronics
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list of possible causes of the high frequency noise which makes the system loosing the lock => to be checked.
(if you have some new idea, I will edit the post)
1- Laser |
Possible causes for the noise in the FP-cavity system, posted by Ronic Chiche at ThomX igloo about mechanics | lasers and optics | vacuum | detectors and electronics 
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4.3 - Vibrations of the mirror mounts due to temperature related to cavity power (the electrons machine is OFF)
1) to test this possible issue, we plan to make a run at low power in the FP-cavity, around 10kW, instead of ~90kW as usual.
for that, I will need to change the diffuser position on axis 18 to get the same error signal for the locking. |
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Vessel cleanliness, posted by Ronic Chiche at Optical room about mechanics | lasers and optics | vacuum
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looking in the vessel of the FP cavity using a UV lamp shows a lot of dust... more dust than outside the cavity !!!
here is picture where one can see a cleaned zone using a finger (with gloves).
question : where does come from this dust ? |
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correlations between vacuum gauges and lock losses @ 20Hz, posted by Ronic Chiche at ThomX igloo about mechanics | lasers and optics | vacuum
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the machine people saw a correlation between BPM jumps and vacuum gauges peaks related to breakdowns in the beam pipe.
these breakdowns could produce some accoustic noise which could be related to our lock losses.
=> we tried to do a corrrelation between our lock losses and the vacuum gauge peaks => WE DON'T SEE any correlation !!! |
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removing of the M1 mirror, posted by Ronic Chiche at ThomX igloo about mechanics | lasers and optics | vacuum
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after trying to increase the power and after moving S3 to try to change the size of the beam on the mirrors, the FPC power suddenly droped.
so, we need to remove M1 to check if it has been damaged.
we placed an iris in reflection of the FPC to keep the alignment for the new mirror M1. |
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removing of the M1 mirror, posted by Ronic Chiche at ThomX igloo about mechanics | lasers and optics | vacuum 6x
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this morning, with Daniele, we took some images of the M1 mirror HR surface :
1- large image span of the mirror surface (~center) before being cleaned :
one can see a lot of spots |
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removing of the M1 mirror, posted by Ronic Chiche at ThomX igloo about mechanics | lasers and optics | vacuum
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This afternoon, we installed a new M1 mirror, the only one for which the box was not already opened.
as the mirror should be "brand new", as the LMA has packaged it, we decided not to clean it with ultra-pure water and to install it
out of the box. |
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Good Xrays production trend, posted by Ronic Chiche at ThomX igloo about mechanics | lasers and optics | detectors and electronics | software
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| this afternoon, we succeeded to get a quite long Xray production trend around 15-20 minutes with a flux above 25k on i1. |
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Current Installed Setup, posted by Manar Amer at ThomX igloo about mechanics | lasers and optics | detectors and electronics
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| Attached is the current setup in ThomX |
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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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this morning we locked the laser and the FP-cavity with ~ 40kW => some HOM appeared "randomly" depending on the power.
we tried to play manually on the L-shape arm :
- first, we moved horizontally to put the L-shape in the beam axis |
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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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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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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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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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!!! 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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!!! 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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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) |