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Entry   fixing CVBG issue, posted by Ronic Chiche at ThomX igloo about lasers and optics | detectors and electronics 
    Reply   fixing CVBG issue, posted by Ronic Chiche at ThomX igloo about lasers and optics | detectors and electronics 12x
       Reply   fixing CVBG issue, posted by Ronic Chiche at ThomX igloo about lasers and optics | detectors and electronics 20240906_151100.jpg
Message ID: 357     Entry time: Fri Sep 6 11:56:53 2024     In reply to: 356
 Author: Ronic Chiche 
 Status: Fixed 
 Type: issue 
 Category: lasers and optics | detectors and electronics 
 Location: ThomX igloo 
 Title: fixing CVBG issue 

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.

 

Ronic Chiche wrote:

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

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.

Ronic Chiche wrote:

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)

 

 

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