Measurement behind P4 (planar mirror)

We installed the 2 CVBG for compression after the amplifier.
We used an interferometric technique with a delay line and combining the two paths in a CCD to measure interferences... see interferences.avi video file
One can notice some misalignement at the end of the video.

After supressing the global shape of the superposed pulses, one measures the amplitude of the remaining fringes (peak-peak or standard deviation) each 250µm of the delay line (500µm of round-trip). one gets the interferences pulse shape with a FWHM of 6ps...
It seems that an 'after pulse' is visible in the interferences.

An other meausurement using a 2 photons photodiode will be used to confirm this measurement.

Yesterday, Loic installed a telescope before CVBG's to reduce the spot size on CVBG's and reduced the incident angle 0.5-1° on them (on the datasheet the specified incident angle is 2.8°).

We used an interferometric technique with a delay line and combining the two paths in a CCD to measure interferences.

After supressing the global shape of the superposed pulses, one measures the amplitude of the remaining fringes (standard deviation) each 50µm of the delay line (100µm of round-trip). one gets the interferences pulse shape with a FWHM of 2 ps... (see curve)
we still see an 'after pulse'.

if the pulse is 1ps long and 100kW is stored in the cavity, it means 3GW peak for the whole beam... it is comparable with the damage threshold of the mirror !!!

Yesterday, Loïc put the CVBG's back to their specified angles.

We used an interferometric technique with a delay line and combining the two paths in a CCD to measure interferences.

After supressing the global shape of the superposed pulses, one measures the amplitude of the remaining fringes (standard deviation) each 50µm of the delay line (100µm of round-trip). one gets the interferences pulse shape with a FWHM of 2.5 ps... (see curve)

from Fabian calculation, at 100kW, with w=2mm, the fluence on mirror should be around 0.05J/cm^2.

from this article (https://www.sciencedirect.com/science/article/pii/S0030402618313275), the damage threshold for SiO2/Ta2O5 multilayers should be around 4.8J/cm^2 @ 1030nm

Last Thursday (20th of February), Loïc and Titouan realigned the stretcher CVBG to its nominal angle and they used an interferometric technique with a delay line and combining the two paths in a CCD to measure interferences.

After supressing the global shape of the superposed pulses, one measures the amplitude of the remaining fringes (standard deviation) each 50µm of the delay line (100µm of round-trip).
one gets the interferences pulse shape with a FWHM of 2.3 ps... (see curve)

14/02/19: The 4 motors but Mby control works. Mby motor home does not bring it to its "middle" position but to the end of its range. Issue circumvented using the higher rights software.

The beam is now going through the cavity windows (from P1 to S2).

The ouput power of the ThomX amplifier has been measured as a function of the 3rd stage pumps current (0A is 1st and 2nd stage turned on).

We measured the total power, the total power without the "donuts" pump signal dumped by an iris and the transmission of a dichroic mirror (for ref see image).

We checked the Dichroic mirror we have : it is a DMSP1000 shortpass dichroic mirror as specified in this post.

The Arrow engraved on the edge of the mirror points on the AR surface !
not on the HR surface...

the AOI is 45°.

Voyage Bordeaux au CELIA avec Jérôme LHERMITE (Loïc et Titoutan)

1^er jour (34°) :

Mesure du spectre et de la puissance des 4 diodes de pompe 3^ème étage jusqu’à ~60W (12A).
Mécanique et câblage ampli.

2^ème jour (30°) :

Soudure des fibres des diodes de pompe 3^ème étage avec les fibres du recirculateur.
Câblage entre les 2 boitiers et fixation des fibres dans le boitier du 3^ème étage.

3^ème jour (26°) :

Connexion refroidissement à eau du recirculateur (chiller).
Soudure fibre CFBG avant 1^er étage (temporaire pour faire des mesure).
Mise en place des éléments 1^er et 2^ème étage sur le support de l’ampli.
Montée en puissance 35W.

4^ème jour :

Adaptation du mode de sortie en contrôlant la position de la fibre avant le collimateur.
Mesure de M².
 

M² mesuré à 10W.
M²x = 1.17
M²y = 1.14

This is a long time issue for the ThomX amplifier : on the 4 pumping diodes available, the 1st diode has a higher temperature than the others around 40°C (see the picture).
the problem comes from the TEC which is not activated (see diodes parameter files in execel format). the related software windows are shaded.

I phoned to Jerome to ask him if one can securely activate the TEC, and he answered "yes".
but once the TEC is activated by loading parameters and modifying the line of the TEC activation, the temperature does'nt fall down as it seems the TEC does'nt work properly.
maybe it is not connected properly ? to be checked...

the result is, as the diode temperature is too high, an alarm is fired and the diode is deactivated... impossible to increase the current.

one has to deactivate the TEC and shut down electrically the amplifier to go back to the starting point.

Conclusion :
- the TEC of the diode 1 does'nt work properly.
- one can't activate it otherwise an alarm is fired and the diode is disabled.
- one should check the TEC connections in the amplifier

This morning, with Ronic, we opened the compressor box to observe if there is any misalignment of the mounts or the CVBG's

This morning we took data of the beam profile at 4 different points to see the evolution of

• the beam shape
• divergence

over distance for all amplification percentages

Data plotted for the distance vs radius for all and divergence in rad is extracted and plotted as a variation of amplification power.

Added is the Excel file with all the details and the PowerPoint for referance

Information about today's work is added to logBook !!

This morning, with Manar and Aurélien, we measure the power directly at the output of the Alphanov amplifier with the 2 compressors CVBG (seeding laser at Frep = 133MHz)
(we had to remove the base plate where the deflector mirrors were mounted to put the large powermeter).

with the previously described procedure, it seems that the Alphanov software is now working and we were able to start immediately the amplifier.

the chiller temperature was set at 25°C but we saw in the Alphanov documentation that the chiller temperature was closer to 20°C.
we did several measurements at 25°C and 20°C and it doesn't change a lot the output power.
so, we set the temperature to 23°C to avoid condensation (if too cold).
we will ask Guillaume what is the best temperature for the chiller.

power measurements:
power ratio     =>   measured output power (with external powermeter, not with the software)
10%               =>               1W
20%               =>               9W
30%               =>               17.6W
40%               =>               26.4W
50%               =>               34.5W
60%               =>               42.5W
70%               =>               49.3W
80%               =>               56.6W
90%               =>               63.6W
100%             =>               ~70W (expected value, not measured)

we stopped the measurements at 90% as we observed a difference in the software between the expected values (previously recorded by Alphanov) and the present ones.
the present values are quite bigger than the ones measured by Alphanov.
Aurélien will call Guillaume to check if it is a problem or not.

answers from Guillaume:

- the chiller temperature has to be set to 25°C
- the power measured with the software can change a little from what Alphanov measured with their laser.
=> one can set power tolerances to 30% in the "caracterisation.csv" file.

on Monday morning 7/11, we tried to restart the Alphanov amplifier which was not turned on since end of april 2022, but it didn't start.

we did a standard "turn ON" procedure :
- check the safety button on the front panel (which has to be released).
- switch on the black switch on the rear panel.
- push the green button on the rear panel
- turn on the key on the front panel
- push the start button on the front panel

normally after switching on the black switch on the rear panel, a light shines in between the red and green big button on the read panel.
but nothing in that case. we just ear a weak "rotating fan" noise coming from the inside of the rack.

normally, after pushing the green button on the rear panel, the start button on the front panel comes to blue.
but nothing in that case.

normally, after pushing the green button on the rear panel and turning the key, the start button on the front panel comes to red.
but nothing in that case.

we tried anyway to connect the amplifier with a computer, just in case of...
but the Alphanov software is not able to connect to the amplifier.

One possible issue could be a dead fuse inside the black ON/OFF switch on the rear panel => one has to check it !

I just tested the fuse inside the black ON/OFF switch on the rear panel => it is OK ! :-(

The laser amplifier controller has been sent yesterday and received today by Alphannov.

they should do the assessment quickly...