last Friday with Manar, we took some thermal images of the Alpnavov compressor box.

I post a small document to summarize some points :

- the 2 mirrors used to make the CVBG injection are polarized thin-film mirrors... thus sensitive to the beam polarization.
there is also a half-wave plate on the input path...
are we sure that the beam polarization is properly set with the Onefive laser injecting the amplifier ?
(Alphanov used their own seeder).

- the CVBG temperature seems normal without too much difference between profiles and values.

- the 2 thin-film mirrors seem quite hot (45°) compared to the rest of the setup.
a basic calculation about power thermally radiated gives an absorbed power of around 0.2W which is equivalent to more than 1000ppm of absorption.
is this estimation correct? could it be the confirmation of some misalignment that traps some power inside the mirror substrate?
 

last Friday with Manar, we took some thermal images of the Alpnavov compressor box.

I post a small document to summarize some points :

- the 2 mirrors used to make the CVBG injection are polarized thin-film mirrors... thus sensitive to the beam polarization.
there is also a half-wave plate on the input path...
are we sure that the beam polarization is properly set with the Onefive laser injecting the amplifier?
(Alphanov used their own seeder).

- the CVBG temperature seems normal without too much difference between profiles and values.

- the 2 thin-film mirrors seem quite hot (45°) compared to the rest of the setup.
a basic calculation of power thermally radiated gives an absorbed power of around 55mW which is equivalent to about 500ppm of absorption.
is this estimation correct? could it be the confirmation of some misalignment that traps some power inside the mirror substrate?
(document corrected to take into account the room temperature)

Last Friday and this morning, with Bruno, we close the ring/cavity valves and put some dry air in the two vessels through a filter to avoid turbulences.

Now, the two vessels are at ambient pressure and ready for opening (to remove the mirrors).

One can let the ambient pressure in the vessels as long as we want, the ring/cavity valves have been chosen to be compatible with the high vacuum in the ring and the ambient pressure in the vessel for a long time.

This morning with Viktor, we opened the 2 vessels and removed the 4 FP-cavity mirrors.

all the mirrors have been put in plastic boxes with labels to indicate which mirror it is,

and with all the HR coatings face down.

the mirrors are in the PLIC room in the "THOMX MIRRORS" box.

Today, after laser was modelocked, we checked the power inside the fiber coming from the Alphanov Strecher box.
it was almost zero, at the nW level.

after doing some very rough alignment, we clearly saw some power (with the powermeter) correlated with the position of mirrors, when turning the alignment knobs.
this is a first step but the output power in the fiber is still very low, about 20nW !

an additionnal 2mm L-shaped hex key is needed to do some walking alignment on the mounts.

This morning with Viktor, we started the alignment of the CVBG and fiber.

we did a better alignment of the 2-pass CVBG.
we are able to the see a spot after PBS (after the 2 CVBG pass) which means the alignment is OK even if it can be improved.

then, we started the fiber injection alignment with the 2 last mirrors (7 & 8 on Alphanov documentation).
we saw that if we unswcrew the fiber to play on the focal position, we are able to improve a lot the power in the fiber.
2-3µW with the fiber screwed => 500µW with the fiber unscrewed.
it means the beam is not enough focused.
I will ask Guillaume Machinet his advice when injecting the 33MHz... do we need to replace the long focal lens just after the Isolator ?
and with which value approximatively ?

we played also with the Schafter+Kirchhoff mount of the fiber colimator (see attached documentation).
we loosen the 2 screws around the eccentric key which adjust the focal position + play on this eccentic key + tighten the 2 screws again.
now, we reached 330µW with the fiber properly screwed.

we have to check the available power before the fiber injection but we have very few place to place the powermeter.
maybe with a small mirror ?

In preparation for tomorrow morning, I did a test with a 45° mount to have a power pickup inside the injection box.

I used the 133MHz laser.
output power measured with the powermeter : 45mW
output power measured with the powermeter + OD2 : 2mW
output power measured with the 45° mount with BB1-E03 mirror with the powermeter + OD2 : 2mW

as expected the BB1-E03 mirrors have a very good reflectance for AOI=45°
the specs give >99% @ 1030nm for both S and P polarizations.

This morning with Manar, we measured the power at different points:
- direct measurement at the output of the 33MHz laser : 35 mW
inside the injection box :
- after the Isolator + focalization lens : 35 mW
- just at the input of the strecher CVBG : 35 mW
- atfer optimizing the alignment of the double path CVBG, in between the 2 fiber injection coupling mirrors : 5,7 mW
(the power is measured after going through the quarter-waveplate and PBS)

I found an old post from Loic claiming that with 27mW input power, we got 9.6 mW after the PBS instead of 5,7 mW !
https://elog.lal.in2p3.fr/FPC/THOMX+commissioning/70
we have to check if the laser wavelength shifted, if the alignment could be improved, if the quarter-waveplate has the right angle,....

then, we tried to couple this 5,7mW inside the fiber using the schafter-kirchoff mount (SKM) but it is a nightmare.
changing the focus and the internal fiber angle is very sensitive, not always predictable and rarely reproductible...
I have to ask Guillaume how he used this mount...
the best power we saw in the fiber is 1mW but after screwing the fixing screws of the SKM, we lose almost all the alignment and we have something around 100-300µW...

This morning with Ronic, using a pickup mirror, we measured the power in different locations along the path of the stretcher box

Output power from oscillator : ~35mW

After the isolator : ~ 35 mW

just before the CVBG : ~ 35 mW

just before the fiber injection : 3 mW

After improving on the mirrors directly correlated to the first line in CVBG and the second reflection line (mirror 4 and 6 on the Alphanov documentation)

we managed to increase the power output just before the fiber to 5.7 mW

To confirm it is indeed the second reflection we see, when cutting the second line and the power drops to almost sero (~70 uW)

We will check the CVBG documentation if it is the maximum power we can obtain after the it due to it's bandwidth !!!!

for the fiber injection :

First without connecting the fiber we checked power after Schafter+Kirchhoff mount we measure 5.5 mW (all power pass through)

when connecting the fiber, we get 300 uW after a quick alignment on the power meter + OD2.

The issue of being too much sensitive arises from the Schafter+Kirchhoff mount, after adjusting the tilt screws and Black knob we got 1.05mW in the fiber for a quick moment.

we had at one point a stable 811 uW into the fiber, but when fixing the mount screws the power drops significantly to 150 uW and it is very difficult to reproduce.

The Schafter+Kirchhoff mount is very difficult to align, waiting on advice from Guillaume Machinet.

I used the 33MHz spectrum measurement : https://elog.lal.in2p3.fr/FPC/THOMX+commissioning/153
fitted by P=P0*sech²((f-f0)/df)
f0 = c/1030m
df = (c/1030nm^2) * 2.5nm

and the strecher CVBG measured data (in attached file with reference D24-02)
to estimate the expected power to be coupled into the fiber.

the corresponding plot shows 3 curves:
- black : the 33MHz laser spectrum "manually fittted" with the sech² function (mentionned at the begining of this post) to match the measured spectrum from the elog.
- blue : the strecher CVBG reflectivity curve from the Excel measured datasheet in attachement.
- red : the corresponding output power after a double path into a CVBG (the reflectivity is applied twice).

with this simulation, one can estimate the power after CVBG to be 12.5 mW for 35 mW of input power.
or 9.6 mW after CVBG for 27 mW of input power which is exactly what has been measured in a previous post by Loic : https://elog.lal.in2p3.fr/FPC/THOMX+commissioning/70

Manar + Victor, today in the morning we aligned the CVBG of the stretcher.

The double path using the mirror mounts, reached up to 5.4 mW just before the injection into the fibers

then we rotated the quarter wave plate and the power increased by a factor of ~ 2 to 10.3 mW

we started with the injection into the fiber by alignment of the 2 mirror mounts.

1) fiber not connected and have everything pass through the mount

2) connect fiber loosely and increase the power in fiber bit by bit until fiber fixed fully

reached power up to 438 uW

alignment not finished using the mounts, there is still also schafter-kirchoff mount.

This morning with Manar, we continued the strecher CVBG alignment and fiber injection procedure :

- we checked the power at the output of the laser and confirmed the measurement after the Isolator : ~ 36 mW
- we tried to improve the power after the strecher CVBG by rotating the quarter-wave plate but it seems we were already at the maximum : ~ 10.5 mW
- we aligned the 2 fiber injection mirrors + schafter-kirchoff mount z-axis : we saw 5 mW at the output of the fiber but it is very difficult to keep the power after swcrewing the 2 z-axis fixing screws of the schafter-kirchoff mount.

we decided to replace the 750mm focusing lens installed by a 1000mm lens.

- we aligned again the 2 fiber injection mirrors + schafter-kirchoff mount z-axis : now, we have ~ 6.2 mW stable at the output of the fiber after screwing the 2 z-axis fixing screws of the schafter-kirchoff mount.

the procedure for aligning the schafter-kirchoff mount is :
- unscrew the z-axis and tilt fixing screws (5 screws in total).
- improve the injection with the z-axis knob and the tilt screws
- tighten very softly all the fixing srews once the optimization is finished => you will lose a part of the alignment but not completely (~ 1 mW level)
- redo a part of the alignment with the 2 aligning mirrors => you should find back the values after optimization.

we let the power-meter at the output of the fiber to check in the next days if the injected power in the fiber changes or not....

it is important to not "kick" the fiber injection box or put anything on it ! as the schafter-kirchoff mount adjustment is soooo touchy...

this morning : still 6.2 mW at the output of the fiber.

the powermeter has been removed and the fiber connected to amplifier input fiber (no EOM connected in between).

Monday 7/11 morning, the power in the fiber was still 6.2 mW

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...

Today, I did a Teams meeting with Guillaume.
He didn't see any problem with the controller.
normally, the controller will be shipped to the lab tomorrow.

I attach an updated schematic of the internal electronics boards and how they are connected to the PSS.

1- when the black switch button is ON, only the Arduino board, which deals with the software in ON.
2- then, one needs to switch ON the big green button => an internal relay allows the power supply to reach the LAL safety board + Central board + MMD boards but these boards are not powered !
3- then, one needs to turn the key ON => the software can access the Arduino board
4- then, start the software => the white LED of the big green button is ON => all the boards are now powered
depending on the safety signals connected to the controller, it will be possible or not to start the diode supplies (with MMD boards).
the 24V DC coming from an external power supply in replacement of the PSS 24V supply is not mandatory to access the software:
we will only see some buttons (Relai 1 and 2 in the software) to be RED (OFF).
 

Yesterday, we received the controller back from Alphanov
and I tested it immediately in the optical room.
if the software is properly talking to the controller, everything works normally.
then, one just have to remember that is mandatory to have the software properly connected to let the controller start electrically (power supply activated on the main boards)

Today, I installed it in the casemate with all the connections to the laser input, output, laser head, safety connections, etc...
and it works properly.

- The power in the fiber from the strecher is at 6.3mW.
the software reads 5.3mW but after a long fiber... then it is OK.
=> one strange thing : it detects 100MHz instead of 33MHz => to be reported to Alphanov !

- Amplifier output power measured after 2 mirrors :
0%                 =>               230 mW
10%               =>               880 mW
20%               =>               8.8W
30%               =>               17W

which are the numbers we had before.... then we are back to normal conditions to continue the commissioning.

today with Manar, we brought everything to make the profile measurement.

the chiller was in error because of the water level : we filled it in.
! warning ! there is no alarm signal, only a message on the screen.

we checked the incoming power measured by the software : 5.5 mW => OK
and we measured the output power (with pump) for :
0% => ~ 300 mW
10% => ~900 mW
20% => 8.65 W
30% => 17W

=> same as before.

the first HR mirror at the output of the amplifier was slightly scratched => we replaced it.

for sake of simplicity, we plan to use first a HR mirror and then 2x wedges for the profile measurement => to be checked next time.
we have to remove secundary beam reflections, then wedges are easier to use than AR/AR mirrors (as the 2 reflected beams are parallele).

at full power, the output power is ~ 70W
after 1st wedge : 2.8W
after 2nd wedge : 112 mW => the power should be low enough to use absorptive filters in front of the beam profiler.