Ronic Chiche, Under Process, info, lasers and optics, ThomX igloo, Laser Amplifier used at 70%

Mon, 02 Feb 2026 15:29:45 +0100

today, I installed a laser dump just before the telescope to avoid any high power (50W instead of 17W usually) issue in the injection line.
last time, we saw some plastic mounts of the polarizers slightly burnt because of some small misalignment.
I used a thorlabs LB2 (see picture) which is able to manage 80W CW or 25J/cm2 pulses => this is OK in both cases : 50W CW / 1.5µJ/pulse for ThomX.

I started the laser amplifier at 70% which produces 50W at the amplifier output and 45W at the input of the FPC.

start : 15h10
immediately, the Temp Amp1 increases from 26°C to 30°C
the Temp Amp2 stays around 26°C
PD_OUT = 79,2W

start + 5-10 min
Temp Amp1 : 31°C
Temp Amp2 : 27°C
PD_OUT = 79,2W

start + 30 min
Temp Amp1 : 31,6°C
Temp Amp2 : 27,5°C
PD_OUT = 79,2W

start + 1h00
Temp Amp1 : 31,6°C
Temp Amp2 : 27,6°C
PD_OUT = 79,2W

start + 1h30
Temp Amp1 : 31,7°C
Temp Amp2 : 27,7°C
PD_OUT = 79,2W

start + 2h00
Temp Amp1 : 31,7°C
Temp Amp2 : 27,7°C
PD_OUT = 79,2W

start + 2h30
Temp Amp1 : 31,7°C
Temp Amp2 : 27,7°C
PD_OUT = 79,2W

Ronic Chiche, Under Process, issue, lasers and optics | detectors and electronics, ThomX igloo, High frequency noise

Mon, 08 Dec 2025 11:17:17 +0100

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" arithmetics).

see attached figure.

Ronic Chiche wrote:

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.
even when saturating the noise signal on the accelerometer, the FPC is not loosing the lock all the time.

then, when a day is very windy, it's possible it could have some effect, but for a normal day, it's seems very doubtful that is the reason...

Ronic Chiche wrote:

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.

So, we still observed a lot of FPC lock losses when the day is windy...
One possible cause could be the large door of the igloo (~20 m²) hitting the Igloo when the day is windy.
I installed the accelerometer on the rail o

Ronic Chiche, Fixed, report, lasers and optics | detectors and electronics, ThomX igloo, Noise issue

Wed, 03 Dec 2025 16:23:40 +0100

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.
we have a little bit more noise and we lose some power on transmission (85kW instead of 90kW) but it worked pretty well.
we had quite long X-rays runs ~ 20 minutes without any lock losses => see the picture.

but we have to keep in mind that maybe it was just a "good" day and an another day can be "bad".
we still have to understand where do these perturbations come from.

the good news is we brought back the previous setting of the FPC.

Ronic Chiche wrote:

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 can remove the cable of the HV to EOM and it does not change the stability of the signals).
when I tried to increase this loop gain in open loop for the PZT loop, I clearly saw an improvement of the transmission signal stored in the cavity.
but when I close the PZT loop, it does not help to get a better locking.
so, at the end, I cancel this loop gain (HV amplifier for the EOM is OFF !) and only the slow feedback loop on the PZT is working.

I reduced the by a factor 2 the range on the PZT loop side to reduce the noise due to the amplif

Ronic Chiche, Fixed, report, lasers and optics | detectors and electronics, ThomX igloo, Noise issue

Mon, 01 Dec 2025 18:03:29 +0100

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 reduced the by a factor 2 the range on the PZT loop side to reduce the noise due to the amplified Laselock (voltage divider 1/2 before the HV amp for the PZT).
and I switched off the laser motor controller (Smaract MCS).
after optmization of the PID parameters, I was able to get back the 90kW we had in the past for 33% laser amp ratio and with a very good stability :
the transmission signal is a line and the reflection signal is almost a line too.
in this condition, I seems that I can lock the laser and the FPC indefinitely.

2) issue with Smaract controller

I put back the Smaract controller only for the CEP channel => one can clearly see a bit more noise on the PDH signal but the transmssion and the reflection signal stay almost the same with a very good stability.

then, I put back the Smaract controller for both channels (CEP and laser cavity length) => the lock was very bad, even after a PID optimization despite the fact it was a "Low Vibration" (LV) Smaract MCS controller.

we tried to change the 3-channels LV controller by a standard 3-channels (not LV) spare controller => it was OK for the CEP channel but not good at all the

Ronic Chiche, Under Process, issue, lasers and optics | detectors and electronics, ThomX igloo, High frequency noise

Tue, 28 Oct 2025 17:31:47 +0100

then, when a day is very windy, it's possible it could have some effect, but for a normal day, it's seems very doubtful that is the reason...

Ronic Chiche wrote:

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.
but we clearly saw that the FPC is much mo

Ronic Chiche, Under Process, issue, lasers and optics | detectors and electronics, ThomX igloo, High frequency noise

Tue, 28 Oct 2025 10:07:48 +0100

Ronic Chiche wrote:

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.
but we clearly saw that the FPC is much more sensitive than the accelerometer... the signal can have a small increase or just one peak and the cavity lock is lost.

then, we can make the assumption that all the "high frequency noise" which produces some lock losses could come from acoustic noise due to the road traffic or from the equipments in the bunker itself.

Ronic Chiche wrote:

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 tri

Ronic Chiche, Under Process, issue, lasers and optics | detectors and electronics, ThomX igloo, High frequency noise

Wed, 01 Oct 2025 10:14:12 +0200

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".

Ronic Chiche wrote:

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.

at the end, we looked at the accelerometer installed inside the housing to check if there was some correlation.
and for the 1st time we clearly saw a 100% correlation beween the accelerometer signal with a noise oscillating above +/-300mV
but we didn't find the origin of this noise.

Ronic Chiche, Under Process, issue, lasers and optics | detectors and electronics, ThomX igloo, High frequency noise

Tue, 30 Sep 2025 15:17:30 +0200

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.

Ronic Chiche, Fixed, info, mechanics | lasers and optics | vacuum | detectors and electronics | cabling | software | utilities, ThomX igloo, Power shut down on September 23th

Mon, 29 Sep 2025 10:22:32 +0200

This morning I did a phase alignment on the PDH signal generator (Rigol DG4102)
this procedure ensure that both phases of the sine wave signals are aligned before finding the correct phase for maximizing the error signal.

so, from now on, in case of power shut down, one just need to :

1) do a phase alignment

2) put the correct phase number on the 2 channels according to the picture (if not automatically done by the generator itself).

340° on channel 1
270° on channel 2

1) and 2) can be done in any order.

Ronic Chiche wrote:

the 33MHz/500MHz RF frequencies from the Ring seems different from the previous state (maybe working at an energy of 50MeV instead of 70MeV which was the previous energy ?).

so, I let the FPC at the present position and wait to discuss if it is necessary or not to move the FPC motors for the correct energy...

Ronic Chiche wrote:

this morning, I restarted all the equipments of the FPC.

everything was fine after being able to get back the correct PDH phase between modulation and demodulation...I got 88kW with 33% amplifier ratio after basic alignment and CEP tuning.

the Pico1 server used for the X-ray photodiode TMD.01 doesn't want to start...
I tried with Astor. the server start to run (red => blue => green colors)
but when I start the Jive panel, it gets down again (red color)... to be solved

Ronic Chiche, Fixed, info, mechanics | lasers and optics | vacuum | detectors and electronics | cabling | software | utilities, ThomX igloo, Power shut down on September 23th

Fri, 26 Sep 2025 11:13:35 +0200

the 33MHz/500MHz RF frequencies from the Ring seems different from the previous state (maybe working at an energy of 50MeV instead of 70MeV which was the previous energy ?).

so, I let the FPC at the present position and wait to discuss if it is necessary or not to move the FPC motors for the correct energy...

Ronic Chiche wrote:

this morning, I restarted all the equipments of the FPC.

everything was fine after being able to get back the correct PDH phase between modulation and demodulation...I got 88kW with 33% amplifier ratio after basic alignment and CEP tuning.

Ronic Chiche wrote:

to anticipate the power shut down on next tuesday 23/09,
this afternoon, I switched off all the equipments except the oscillator connected on the UPS.

Ronic Chiche, Fixed, info, mechanics | lasers and optics | vacuum | detectors and electronics | cabling | software | utilities, ThomX igloo, Power shut down on September 23th

Fri, 26 Sep 2025 11:08:21 +0200

this morning, I restarted all the equipments of the FPC.

everything was fine after being able to get back the correct PDH phase between modulation and demodulation...I got 88kW with 33% amplifier ratio after basic alignment and CEP tuning.

Ronic Chiche wrote:

to anticipate the power shut down on next tuesday 23/09,
this afternoon, I switched off all the equipments except the oscillator connected on the UPS.

Ronic Chiche, Fixed, info, mechanics | lasers and optics | vacuum | detectors and electronics | cabling | software | utilities, ThomX igloo, Power shut down on September 23th

Thu, 18 Sep 2025 18:29:04 +0200

to anticipate the power shut down on next tuesday 23/09,
this afternoon, I switched off all the equipments except the oscillator connected on the UPS.

Ronic Chiche, Fixed, info, mechanics | lasers and optics | detectors and electronics, ThomX igloo, Accelerometer measurement

Tue, 16 Sep 2025 17:41:28 +0200

with Daniele, we placed the accelerometer on top of the fiber amplifier box which is inside the housing.
the goal was to try to detect a correlation with some possible accoustic noise coming from the bubbles of the water, cooling the amplifier box baseplate.

we monitored a long trend of the transmission which is perturbated when high frequency noise arises, and the accelerometer signal.
the long trend plots only the peak-peak value of a full 1 second acquisition every 2 seconds during ~2500 pts equivalent to ~5000 seconds = 1h20

on the plot, the top white signal is the transmission pk-pk and the bottom red signal is the accelerometer pk-pk.
we don't see any correlation except at 600-700 pts because Daniele entered the bunker and slightly knock on the bottom of the optical table several times.
and at 1950-2300 pts, because he opened the housing (much more noise recorded by the accelerometer) and then it close it again.

he also try to knock on the amplifier controller rack which is placed on the ground, below the table, but he didn't see any correlation with some cavity lock losses.

=> no clear conclusion.
except that the noise seen on the transmission when the housing is open is close to the "high frequency noise" we observe... could it be some accoustic noise coming from elsewhere ?

Ronic Chiche, Fixed, info, lasers and optics | detectors and electronics, ThomX igloo, polarization measurement of the FP cavity beam

Tue, 16 Sep 2025 12:32:52 +0200

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).

2) then, we installed a high power PBS CCM1-PBS25-1064-HP(/M) with a transmission of 89% of the P-polarization @ 1030nm
We measured 66.5kW in transmission of the cube.

3) then we installed a half waveplate to find the optimum angle => 77kW measured at an angle of 342°
(almost no power has been observed in the vertical polarization state of the PBS).

Then we rotated the waveplate to find the previous measurement => 66.5kW at an angle of 348°
(we checked that adding the waveplate in the path almost does not change the measured power)

Conclusions :
- the FP cavity polarization is almost horizontal (P-polarization) and linear (77kW ~ 89%*82.5kW)
- the angle of the polarization is roughly 2*(348-342)° = 12°

Ronic Chiche, Fixed, info, detectors and electronics, ThomX igloo, Power shut down on August 29th

Thu, 28 Aug 2025 18:01:46 +0200

after alignment, CEP adjustment and optimizing the PDH phase, I got back ~92kW in the FPC for 33% amplifier ratio.

Ronic Chiche wrote:

This morning, all the equipments have been switched off due to a power shut down tomorrow morning.
Only the Onefive oscillator is still ON, connected to the Uninterruptable Power Supply (UPS).

ELOG THOMX commissioning

Ronic Chiche, Under Process, info, lasers and optics, ThomX igloo, Laser Amplifier used at 70%

Ronic Chiche, Under Process, issue, lasers and optics | detectors and electronics, ThomX igloo, High frequency noise

Ronic Chiche, Fixed, report, lasers and optics | detectors and electronics, ThomX igloo, Noise issue

Ronic Chiche, Fixed, report, lasers and optics | detectors and electronics, ThomX igloo, Noise issue

Ronic Chiche, Under Process, issue, lasers and optics | detectors and electronics, ThomX igloo, High frequency noise

Ronic Chiche, Under Process, issue, lasers and optics | detectors and electronics, ThomX igloo, High frequency noise

Ronic Chiche, Under Process, issue, lasers and optics | detectors and electronics, ThomX igloo, High frequency noise

Ronic Chiche, Under Process, issue, lasers and optics | detectors and electronics, ThomX igloo, High frequency noise

Ronic Chiche, Fixed, info, mechanics | lasers and optics | vacuum | detectors and electronics | cabling | software | utilities, ThomX igloo, Power shut down on September 23th

Ronic Chiche, Fixed, info, mechanics | lasers and optics | vacuum | detectors and electronics | cabling | software | utilities, ThomX igloo, Power shut down on September 23th

Ronic Chiche, Fixed, info, mechanics | lasers and optics | vacuum | detectors and electronics | cabling | software | utilities, ThomX igloo, Power shut down on September 23th

Ronic Chiche, Fixed, info, mechanics | lasers and optics | vacuum | detectors and electronics | cabling | software | utilities, ThomX igloo, Power shut down on September 23th

Ronic Chiche, Fixed, info, mechanics | lasers and optics | detectors and electronics, ThomX igloo, Accelerometer measurement

Ronic Chiche, Fixed, info, lasers and optics | detectors and electronics, ThomX igloo, polarization measurement of the FP cavity beam

Ronic Chiche, Fixed, info, detectors and electronics, ThomX igloo, Power shut down on August 29th