we had to move the laser cavity motor to find the resonances and change a lot the CEP.

the CEP motor is at -524.1µm

we got ~75kW in the FP cavity without alignment but with CEP optimization.

the coupling (the cyan color) is ~ 62% !

=> we need to do some alignment

after doing some alignment (walking procedure on the Y axis), and CEP optimization, I got 83kW for 33% on the laser amplifier with a coupling of ~60%

=> we have to check the input power after the amplifier.

I adjusted the FP and laser cavity motors to have a small 33MHz detuning with the RF reference (~10 Hz of beating @ 33MHz)

pb : I don't see the 500MHz beating signal => to be checked

during the motion of the FP-cavity motors, I observed a systematic delock when moving MOT.06 on P1z and no delock with MOT.03 on P4z when I move by 10 steps.
Kevin checked that both IcePap controller have the same configuration and then, the problem is maybe coming from the rust observed on the mechanic.
 

this morning with Daniele, we are measuring the amplifier power just before the FP-cavity.
Casemate temperature @19.5°C

@0% : 205mW
@10%: 755mW
@20%: 7.44W
@30%: 14.3W
@33%:16.3W
@40% : 20.3W
@50% : 24W
@60% : 26W

=> there is a power issue !!!

the normal casemate temperature should be in between 21 and 22°C.
cf this post (https://elog.lal.in2p3.fr/FPC/THOMX+commissioning/133) to get previous amplifier power.

=> it seems we need to redo the compressor CVBG alignment !
first, we will check the amplifier power before the compressor.

After the summer power shutdown, I restarted all the equipements and got quickly ~80kW for 33% amplifier ratio with CEP optimization and without Alignment optimization.

CEP motor position : -506µm

amplifier power measurement before the compressor CVBG.
we used a mirror in between the amplifier output and the compressor + a 2-mirror periscope to match the powermeter height.

amp ratio (%)          power (W)

0                               0.7
10                             1.65
20                             13
30                             25
40                             37.7
50                             50.5
60                             62
70                             74
80                             86
90                             99
100                          110

we had an alarm @100% of amplifier ratio => the reason is not clear... maybe it's coming from a discrepency between some internal measurement and the expected value.
we checked the power after the alarm => still OK

conclusion, the amplifier seems to be OK... we need to redo the alignment of the compressor CVBG.
 

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
2) ajuster les iris d'alignement du faisceau de l'ampli pour être sur de ne pas perdre la référence de l'axe de la CFP

3) installer des wedges haute puissance à proximité du compresseur + beam profiler
4) verifier la forme du faisceau au beam profiler en fonction de la puissance de l'ampli

5) ouvrir le boîtier du compresseur
6) prendre des images du boîtier à la caméra thermique en fonction de la puissance

7) éventuellement shunter le 2e CVBG avec un D shape et regarder le mode et caractéristique en sortie d'ampli.
8) ajuster l'injection dans le premier CVBG ou le second ou les deux en fonctions des résultats précédent

here are some useful logbook posts:

D-shape + images thermiques du compresseur qui peuvent servir de référence :

https://elog.lal.in2p3.fr/FPC/THOMX+commissioning/147

https://elog.lal.in2p3.fr/FPC/THOMX+commissioning/150

post des images du faisceau en fonction de la puissance de l'ampli :

https://elog.lal.in2p3.fr/FPC/THOMX+commissioning/135 (et autres posts du fil)

https://elog.lal.in2p3.fr/FPC/THOMX+commissioning/195 (et autres posts du fil)

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 time ago to match the new RF frequency?).

3) we opened the compressor box and found out the beam on the last mirror was really on the border => we have to move it.

=> we recorded several beam profiles at 20-70% of amplifier ratio (see images before realignement)
above 50% of amplifier ratio, the beam is deformed.

=> we realigned the 2 last mirrors of the compressor and compensate the axis displacement with the 2 inches injection mirrors at the output of the compressor to get back the telescope axis.
amplifier ratio (%)                 power after compressor (W)
0                                                 0.286
10                                               0.91
20                                               8.6
30                                              16.7
40                                              25.5
50                                              34.5
60                                              42.5
70                                              50.0
80                                              57.0
90                                              64.0
100                                            70.0

small power drop for ratio < 40% compared to previous measurements : https://elog.lal.in2p3.fr/FPC/THOMX+commissioning/133

the power is back => OK ! :-)))

we took some images with the beam profiler at high power after the realignement (see images after realignement)

tomorrow, we have to realign the amplifier beam axis to the CFP axis.

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.

we also played on the 1/2 and 1/4 waveplates to tune the polarization.
we see very clearly the locked reflected signal changing without almost changing the transmission !

Aurélien suggested to slightly focusing the beam in the DET36 photodiode to have a better estimation of the coupling.
presently, the beam is clearly larger than the DET36 photodiode area which artificially increases the measured coupling.
(I cannot use a DET100 because I need 500MHz BW to get some RF signal for beating with the 500MHz reference signal).

I added a +75mm lens in front of the DET36 reflection signal photodiode => now, the beam is rougly 1-2mm diameter, centered on the DET36.
when I optimize the alignment and the CEP, I get 86-87kW in the CFP and 45% coupling => cf plot

end of the CVBG issue posts.

after redoing the alignment of the CVBG, we got back the initial power in the FPC (87kW)

now, I checked the RF locking signals on the 2nd oscilloscope.
I get a strange ratio between the 33MHz beating and the 500MHz beating signals.
beat @ 33MHz ~ 40kHz !
beat @ 500MHz ~ 700Hz !

maybe the 33MHz generator frequency is not matching the 500MHz RF frequency ?
 

now, the Ring RF frequency is set to 500.067MHz.

so the CFP/laser frequency should be 500.067MHz/15 = 33.3378MHz.

the frequency was set to 33.378MHz !!! => it explains the frequency shift only on the 33MHz beating => I corrected the frequency on the generator and informed Nicolas Delerue.

=> now, I can try to lock the CFP to the RF frequency.

I changed a little bit the locking parameters (see picture) for the RF/FPC loop and it locked rapidely.

I asked Vincent to connect on the same scope the synchro signals to check if the FPC lock was OK => he connected 33MHz signals coming from the laser and from the 33MHz RF generator.
=> the signals are not locked even when the FPC seems to be locked to the RF.

=> it can be normal because he forgot to connect also the synchro trigger signal which gives the moment of synchronization of the machine... to be finished on Monday.

this morning, with Vincent :

- we added the 10Hz trigger to the CH2 on the remote scope (192.168.229.21) to check the synchronization at the right timing.
CH1 : 33MHz RING
CH2 : LINAC/RING synchro signal
CH3 : 500MHz RING
CH4 : 33MHz FPC

we successfully lock both laser on FPC (87kW for 33% amp ratio) and FPC on 500MHz RF.
we saw the result on the scope.
suprisingly, the FPC/RF lock seems much robust than before.

the only problem is the MOT.06 which make the lock being lost at almost every move.
one reason could be the rust on the mechanics... we can try to change the position of both plan mirror motors to work in a proper region.
before, it was working well at -900 000 steps on MOT.06, now it is -780 00.
it's a quite long travel...

end of this posts thread

this morning, I try to find a new region for MOT.03 and MOT.06 where we can move them without unlocking the cavity.

I started from the position:
MOT06 : ~ -785 000
MOT03 : ~ -200 000

and I do -10 000 steps (dz = 10k x 6nm = 60µm) at a time on both motors.
previously a good region for MOT.06 was -900 000 !

I moved also the laser cavity by 40µm to cancel the beating with the RF frequency.

MOT06 : ~ -795 000
MOT03 : ~ -191 000

Max power after optimazing the CEP ~ 65kW => I need to realign => 78kW
I need to increase the D parameter on the PID to compensate the (85kW / 78kW ratio).

I changed the MOT.03 and MOT.06 speed to 30steps/s => it seems a bit better.
but I still see some lock losses during a move.

.... to be continued...

this morning with Daniele, we did a quite long run with this motor position and it seems we don't lose the lock too much.

the motor positions are:

MOT.03 (M4): -186 500 steps

MOT.06 (M1): -797 500 steps

we got 85kW after CEP optimization and rough alignment optimization.

On Friday 11th of October, due to the Yvette flooding, all the AC power of ThomX have been shut down.
After the shutdown, I had to restart the Onefive oscillator but the laser modelock was lost.
I had to do a step of 1mm at 10mm/s with the Smaract motor on the rep rate channel (CH1)

After the step, the laser was mode-locking again, and I put it back in the original position at a much lower speed, ~10µm/s, to prevent a new modelock loss.
the power detected by the laser amplifier software is still above 3mW! => OK

Surprisingly, the laser amplifier software is not able to detect the oscillator frequency.
hopefully, the internal photodiode of the oscillator is sent to the CH4 of the R&S scope (192.168.229.21)
and we measured a correct 30ns of period, corresponding to 33MHz.

Because all the safety procedures are not fulfilled, the laser amplifier is not granted to start.
Maybe it is the Reason for the lack of measurement => to be verified later
 

This morning, I verified the reason why the seeder frequency was not displayed on the amplifier software screen:

one needs to start the amplifier (even at 0%) to see the seeder frequency !!!
now, we have 33.371MHz as expected ! => OK

the last thing to do is to tune again the PDH demodulation frequency, as the generator has been shut off during the AC shut down.
 

After the new Yvette flooding of the last week and the consecutive AC-shut down, I restarted this morning the laser with the same procedure (step of 1mm at 10mm/s with the Smaract motor on the rep rate channel (CH1)).

now, we have again 33.371MHz and 3.1mW input power as expected ! => OK

the last thing to do is to tune again the PDH demodulation frequency, as the generator has been shut off during the AC shut down.

For the modulation/demodulation generator for the PDH signal,
after a power shutdown, on can :
1) restart the generator to get the correct parameters:
CH1:3Vrms on 50 ohms @ 8.4MHz (demod)
CH2: 100mVrms on 50 ohms @ 8.4MHz (modulation on EOM)

2) do an "Align phase" on the generator

3) put 270° on CH2 (0° on CH1) to get the max Error signal
and use a "positive" sign on the Laselock : cf https://elog.lal.in2p3.fr/FPC/THOMX+commissioning/365

this morning, with Daniele, we checked the amplifier power, right after the CVBG (the power meter has to be placed on a metal plate above the large table hole), and just at the input of the FP cavity, after the 1/4 and 1/2 waveplates (the power meter has to be placed on flat beam dump+ Thorlabs beam dump + V metallic mount to be at the right height).

we compared with the power measured the 9th of september : https://elog.lal.in2p3.fr/FPC/THOMX+commissioning/356

the 3 collumns are the measurement close to the CVBG on 9th of september / same position today / just befor the FPC today

amplifier ratio (%)                 power after compressor (W)                 (new) power @ CVBG   (new) power @ FPC      ratio FPC/CVBG power (%)
10                                               0.91                                                  0.93                                    0.83                                       89.2
20                                               8.6                                                    8.6                                      8.0                                         93.0
30                                              16.7                                                  16.9                                    15.8                                        93.5
40                                              25.5                                                  25.6                                    24.0                                        93.7
50                                              34.5                                                  34.6                                    32.5                                        93.9
60                                              42.5                                                  42.5                                    39.5                                        92.9
70                                              50.0                                                  50.0                                    45.0                                        90.0

we observed with the viewer the beam on the powermeter.
at 70% of amplifier ratio, the beam size is as big as the powermeter detector.
then, the 93% to 90% transport efficiency drop could come from this "too small" powermeter detector.

we observed also at this power ratio (70%) that the 1/4 and 1/2 waveplates were not perfectly centered and we burn a part of the platic mount at this power.

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.