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

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.

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...

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 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 ?

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.

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.

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 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 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.

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.

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°.

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 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.

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.

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 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?
 

For better comparison ,

the measurements done previously with 2 CVBGs was done at ~ 30 cm and the one done on Friday was for 1 CVBG is at 1 m

so we did additional measurement for 2 CVBGs at 1 m, for 20 , 50 and 70 % amplification 

we clearly see the similar deformation at high power.

Conclusion : the effect is most likely coming from the 2nd CVBG

At 70 % victor optimized the horizontal axis for the injection mirror into 2nd CVBG , we see an improvement in the Gaussian fit on Horizontal and vertical axis of ~ 2%

Victor, Ronic, Manar

Today  was dedicated to the study of the CVBG, and it's effect on the beam profile

we opened the box containing the 2 CVBGs : The 2CVBG are glued from the bottom on a copper surface .

Using the beam viwer, the beam line inside the two CVBG is not at the exact center but not at the edges too and not hitting the boarders.

From the sides you see two lines, one is reflection on the metal.

To observe the effect of the first CVBG by itself, we blocked the second reflection into the 2nd CVBG.

By placing the D-shaped mirror just at the entrance of the 2nd CVBG (there was just enough space to put it)

Beam Profiler + OD 10E + OD 30E + OD(not known) placed at ~ 1 m from the output of compressor.

We see clearly a much better circular shape of the beam and a better Gaussian fit,

only above 90% where we see the fit percentage going down to ~ 86% and on just the Horizontal Axis.

Pulse Duration FWHM = 12.9 ps