Picture of the installed mirrors inside the FP cavity.

To install an Iris instead of a mirror :

One has to remove manually the orange nuts and replace the mirror mount with the Iris mount.

https://atrium.in2p3.fr/0dded51a-1cb0-43e6-ae0d-626cd5db7078

a lot of schematics regarding the FP cavity are stored by the mechanic group on the Atrium repository.

this morning with Manar, we did a cavity mode axis change.

we checked the cavity mode centroid position on the beam profiler (placed behind P4) and changed it by roughly 1mm on the X-axis and by 500µm on the Y-axis.

for doing that, we played only on the S2 mirror while the cavity is locked and we slightly changed X and Y motors, step by step, and we realigned the laser beam with external injection mirrors when needed.

in the end, we were able to improve the transmission power by roughly 25% (810mV to 1020mV on the Transmission photodiode on the scope).

we did several Finesse measurements after that: 4950, 5190, 5100, 5120, 5200 => ~ 5100

compare to the previous Finesse value, around 4200, this is also roughly 25% better, in agreement with the transmission power increase.

conclusion: it seems the Finesse, thus the losses are almost the same "everywhere" on the mirrors => we need to clean them or replace them.

Aurélien, Manar, and I spent more than 2h trying to start the software communicating with the Alphanov amplifier controller.

each time, we had a problem with the software, asking to switch OFF and ON the controller before being able to switch the amplifier diodes ON.
we switched OFF and ON many times without any success.

in the end, Aurélien called Guillaume from Alphanov... and without changing anything, it worked... strange!

one possible problem could be the correct detection of Frep of the seed laser (OneFive).
as we didn't check the signal coming from the seed laser, it could be the reason... to be confirmed.

the present status for the controller is:
- the power connector (on the rear side) is ON
- the green relay (on the rear side) is ACTIVATED
- the key (on the front side) is OFF
- the emission button (on the front side) is OFF

the normal procedure to start the controller is:
- switch the front side key ON
- start the software (possible error msg asking to switch OFF and ON the power button: don't do that)
- switch the emission button on the front side (which is red) ON
- switch the preamplifier button ON
=> all the software LEDs should be green and the PD_PULSE window should indicate 133.33MHz
otherwise, try a RESET on the software and restart the procedure (and pray).

at the end of the day, we successfully switched ON the preamp and increased the Power adjustment around 20% to get something about 10W on the big PowerMeter placed at the output of the amplifier.
=> we need another day of practice to be more confident with the software!

Additional information related to the injected power into the amplifier fibers.

power = 4.45 mW (as shown from the software)

the minimum to inject into amplifier is 2 mW

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.

Software Works well and is operational.

Just closing the log series!!!

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.

On the 8th of July, the SN2439 33MHz laser was returned from NKT to our lab, being repaired.

it stayed all the weekend to warm up in the optical room and has been turned on on Monday.

the mode-locking was not working (28mW output power and a CW line for the optical spectrum), thus I "kicked" the laser with 100µm moves on the motors.

now, the laser is mode-locked with 42mW output power and the expected optical spectrum.
 

This morning, with Aurélien and Daniele, we did the swap between the 33MHz and 133MHz oscillators.

now, the 33MHz oscillator is on ThomX inside the casemate.
it has been restarted and some laser is going out.
it has been screwed on the metal plate, roughly aligned with the Alphanov "fiber injection and strecher" box.
tomorrow, we will do the fine alignment with this box and check if the laser is properly modelocking.

the 133MHz oscillator is back in the PLIC optical room.
it has been restarted and some laser is going out.
it seems there are no pulses at the output... it seems we have to trigger the modelock.

Yesterday with Aurélien, we try to make the laser modelock using the Smaract translation stages embedded inside the laser head.

unfortunately, we got some errors when we try to do the "calibration" and "reference" of both Smaract stages !
we contacted by email M. Nicoul to help us on this topic

Today, we removed the 33MHz and its controller and motors controller from the casemate to install it in the PLIC room.

with the help of M. Nicoul, we did a first check of the PZT capacitance of each stage (~ 60nF)
for channel 0 (Frep), the measured capacitance is 53nF on the laser head
for channel 2 (CEP), the measured capacitance is 63nF on the laser head
between pins 1 and 9 of the DB9 connector.

M. Nicoul says that these values are compatible with the reference values ~ 60nF, then the PZT translation stages are OK.
Then, the controler is maybe damaged.
One has to find a new one to test the stages.

Today, we used an "ELI-NP" Smaract controller made with these 2 references :
MCS-3CC-ETH-TAB (SN 2271) => main controller
MCS-3S-EP-SDS15-TAB (SN 2472) => sensor module

with the ethernet parameters:
IP : 10.0.52.226
MASK: 255.255.255.0
GW : 10.0.52.01
PORT : 5001

one has to configure the device into PTC or MCS software as :
network:10.0.52.226:5001

then, one can access the Smaract controller and move both Frep and CEP stages.
we succeded to make the laser modelock again ! :-)
the output power is about 42mW !

Yesterday, we put back the 33MHz oscillator into the casemate with the new Smaract controller.
after switching ON the laser controller, we saw some power at the output but we have to check if the laser is modelock or not.

Today, we succeded to make the laser modelock.
the ouptut power is above 35mW (the powermeter was saturated)
here is a screenshot of the signal on the scope.

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 ?