today, we observed on the photodiode used in reflexion of the cavity, that its voltage level stops increasing after 50% of power for the laser amplifier when the cavity is not locked (the FP-cavity is just a reflective mirror).
the photodiode itself is not saturated (low power sent after a wedge and an absorbing filter) and the reading is done on 50 ohms.
so we are investigating the reason of this "saturation".

1) we did a beam power measurement just after the 2 mirrors, right after the amplifier, with the "big" powermeter:

power ratio        Power (W)
10%        =>  0.9
20%        =>  7.7
30%        =>  15.5
40%        =>  24.2
50%        =>  33
60%        =>  41
70%        =>  48
80%        =>  55.5
90%        =>  62.2
100%      =>  68

plot in attached file

2) we did the same measurement after the periscope:

power ratio        Power (W)
10%        =>  0.82
20%        =>  7.7
30%        =>  15.5
40%        =>  24.2
50%        =>  32.6
60%        =>  39
70%        =>  44
80%        =>  47.4

we clearly see a power reduction from 50% and beyond.
with the viewer we saw 2 effects : a slight clipping in the telescope and some speckles on the periscope mirrors mainly.
the laser is also slightly shifted on the 2nd mirror after the amp.
it is possible the laser beam moved due to thermal effect => we will need to realign properly the whole injection line and be aware about mirrors and lens cleaning !

3) we did some measurements using 2 wedges with the "small' powermeter in reflection of the cavity.
we remove the small aperture half-waveplate to see the effect and we used a lens to focalize the beam:
the half-waveplate has an effect on the reflectivity of the wedges, this is the reason of the difference in the measurement.

                                                               Power (µW)
power ratio        with lambda/2           w/o lambda/2             w/o lambda/2+lens
10%        =>           12.4                           4.8                               5.1
20%        =>            132                            48                                51
30%        =>            262                            96                               101  
40%        =>            370                            137                             147   
50%        =>            420                            158                             175 
60%        =>            430                            165                             181

we observe a clear "saturation" after 50%-60% which is very similar to what we observed with the photodiode in reflection when the cavity is not locked.
the small iris used in front of the injection window of the cavity is a good "candidate" for clipping the beam at high power (we observed it was still quite hot after stopping the beam).
=> we have to redo the measurements after removing it.

on friday 23/06 afternoon, after scanning the hexapod z-axis, we observed a cut of the power stored in the FP-cavity (with constant input power/coupling) at both ends of the scan, due to the losses of the beam-pipe aperture.
we placed the hexapod exactly in the middle of this range ~ z=-1.68 mm (which is not the middle of the maximum range of the hexapod), we opened the slits on the X-table and we found the first signal.

after scanning, shuting the laser beam and electron beam ON and OFF, we confirmed this signal was coming from X-rays.

on monday 27/06, roughly in the same condition (25kW of power stored in FP-cavity), we scanned properly the same z-axis with the hexapod and we measured the pico-ampermeter current related to the produced X-rays to get the approximated size of the laser and electron beams at the IP position : see the raw data.

Daniele did the data analysis : see the attached analyse_profil_vert_X-1.pptx file
the total rms size (sigma of the Gaussian profile) is 100µm.

this morning, we measured the FP-cavity waist size by measuring the waist size of beam at the focal distance of a lens used after the spherical mirrors.
we measured the rms size of the FP-cavity mode to be 60µm in agreement with simulations, which leads to 80µm rms for the electron beam waist size.

Yesterday,

• we installed the second high power reflecting mirrors at the output of the amplifier.
• We aligned and installed a telescope that has adjustable distance between the 2 lenses of -100 mm, and + 200 mm, with approximate diameter at the injection window of  ~ 4.5 mm.
• Amplifier was turned on only at the first stage only (output power ~ 300 mW) aligned and injected into the cavity.
• Measured the repetition frequency of the One Five oscillators, Frep = 33.326239 MHz
• Changed the FSR of the cavity to match it.
• Using the Piezo scan on the oscillator, we observed 00 Mode, Fundamental. the shape is the same 
• We see transmission on the diode, but there was zero coupling observed (yet to be investigated experimentally )
  • a reason could be the CEP of the oscillator ,
  • bad matching of the beam waist position,
  • noise from the amplifier (as we were operating it at very low power)
  • additional alignment needed,

• On Monday with Daniele,
  • we did full characterization of amplifier beam @ 10% amplification, adjusted the telescope accordingly and injected into the cavity aligned and improved on the fundamental mode.
• On Tuesday with Daniele and Kevin
  •  I added a low pass filter between 1 - 1.9 MHz on the reflected signal, to reject the oscillator signal (33.33 MHz)
  • removed the external resistors on the signal, only the internal resistance of the oscilloscope used ( transmission : 1 M ohm  , Reflection : 50 ohm  )
  • We connected the motors to control the CEP and adjusted on them until we reached ~ 5 -10% coupling
• Images:
  • 1st : showing the size of the beam just before injecting into the cavity @ 10%
  • 2nd: signal with only improved alignment (not CEP adjustment yet), no low pass filter added yet
  • 3rd : zoom on the signals (reflection and error) while adjusting on the CEP
  • 4th :attempting to lock the cavity , after getting the max coupling using the CEP motors

Note : the voltage ranges are not the same between the images

Added Note: the coupling we get is at low power, only preamplifier is on (~ 300 mW)

was done at the end due to excitation of higher order modes.

Wanted to improve the fundamental first, then increase the power.

Today with Ronic and Daniele we attempted to lock the cavity, but the alphanov amplifier did not turn on because of an error in MMD3 (related to the third stage)

the new error is having the MMD3 error show on the alarm window of the LAL software, and having the Alarms on the line 3 of the alphanov software red for both EXT/CPU and Laser T Max (never been red before)

this is after a 2-week work stop, but the last time when Daniele changed the fiber connector it worked for 3 hours with no errors.

Ronic, is in contact with Guillaume from Alphanov to fix the issue !!!

Work scheduled all Wednesday, in hopes the issue is fixed by then.

This morning, while trying Guillaume solution of disconnecting the 24 V necessary to the second and third stage and raise the threshold of Temp preamp 1 (to only operate the ampli with first stage only)

Ronic disconnected the 24 volt connection, turned on amplifier LAL software but no MMD3 error or a big temp on Temp preamp 1 , software worked fine with no issue. 

we connected the 24 V again and the software worked with no issues.

Still not sure what happened for it to work correctly !!!!!!!!!!

• We used the amplifier at 0% all day with no errors (to test , I turned it for 10 minutes @ 10% with no error too)
• We changed the lase lock box with ThomX one (having Ethernet connection), it was connected to computer and works ok
• Ronic installed a signal amplifier for the PDH error signal. (yet to be fully optimized)
• we see a better coupling than before in the cavity.
• The dominant mode is 00 mode, but we see many higher order modes, need to alight better.

Yesterday, with Ronic we locked ThomX cavity on the second resonance

Laser : 33.36 MHz , Amplifier : 0 % (worked with no errors all day)

adding image for the lock on the second resonance (locked), 00 Mode image, fit, Beam measurements

and image of the first resonance signal (not locked)

Info : when locking on the secondary resonance, we aligned better and adjusted on the oscillator CEP and increased the transmission signal 

Controllers connected to computer

through Ethernet :

• Cavity Mirror motors
• Lase lock
• oscillator CEP and Frequency motors (easier to follow the drift with this controller, and we can see it moving)

by USB :

• Amplifier controller

Today, I installed a power meter at the transmission point of the 1st spherical mirror , transmission 3 ppm (direct from cavity window beam profiler, no filter)

We locked the cavity at 2 different resonances of the fundamental mode, the lock in both cases was stable for a round 1 minute.

at different transmitted power of 33.85 uW ( 11 W average inside cavity) and then locked again at 82.65 uW (27.5 W average inside cavity) transmitted power 

Note : the coupling is almost zero for both of the resonances locked !!!!

Oscillator : 33.33 MHz ( 33.356 MHz , frequency read on LAL software)

power injected into amplifier (after injecting into fiber and an EOM) : 3.886 mW (on LAL software)

Amplifier power : 0% (injected power into cavity ~ 300 mW)

Both images of oscilloscope have same voltage scales, only difference timescale and the color code is : 

yellow : transmission

blue    : reflection

green : piezo voltage

red     : error signal

Today with Ronic,

starting with major events that happened (Water circulation + ThomX valves )  

• Early in the morning a company worked on the water network, it seemed it was not restarted properly so there was no water circulation in the main ThomX pipes.
  • There was an error on the ThomX amplifier chiller , which was noticed at the end of the morning work , where we couldn't find the cavity resonance , could be due to the temperature increase of the amplifer.
  • Solved :  the issue was solved by restarting the water network and the amplifier chiller was restarted an no error found and temp. Stabilized around 25°
• Around 12h15 ThomX there was a power cut off for less than a second (micro cutt), which cased all the valves to close, the valve air compressor did not restart after the power cut off, we restarted it with Daniele in the evening with the help of Marie and the valves open around 5-6 bar , you will see then all the controllers green and the valves will open.

Results of the day :

• All the power supplies and function generators are under the table, nothing on the table (reduced noise on the signal)
• EOM of Oscillator Off (for now, might turn on if needed)
• Amplifier on 0% , output ~ 300 mW
• Locked on the first resonance of the cavity,  lase lock parameters to be optimized better
• Transmitted power increased to ~ 267.2 uW
• Average power inside cavity = 89. 06 W , peak power = 0.2 kW (pulse width = 12.6 ps , frep = 33.36 MHz )
• current effective cavity gain > 300 

Oscilloscope :

•  error signal, not shown as it was too noisy to have in the image
• blue : reflection (low bypass filter ), yellow : transmission (resistance of 100 k ohm added), green : piezo signal
• 1st image : showing lock and scan regions.
• 2nd image: time zoom on the locked signal 

oscillators controller / smartAct:

• Frequency and CEP control , the parameters in the photo attached are the best for the moment to see the smooth change of the resonance peaks when operating the motors, and we can stay FSR range and compensate the variation easily. 
• even though we stayed at closed loop (for easier adjustment), we still managed to lock , will try to switch off later to see if reduces a lot of noise. 

In the morning, we locked on the first resonance. With an increase on the amplifier power @ 20-25% and 30%, which reduced the noise

we manage to get a coupling when improving the CEP up to 55 - 60 % coupling : put there is still a drift on the CEP

The controller for the oscillator frep and CEP produces a lot of noise, even if it is disconnected. we need to switch it off to remove its effect (Kevin will order a new one)

The image attached is of the oscilloscope lock on the first resonance @30% amplifier power ~ 10 W injected into cavity,

transmitted power ~ 36 mW (cavity average power 12 kW)

cavity effective gain > 1200

in the afternoon, we installed and aligned a gentec power meter we can monitor from the computer. (will need to buy a permeant one for ThomX)  

there was an issue with the laselock USB connection, yet to be solved.

and the control of the computer.

The computer is possible to connect from the control room,

we are able to run remotely the amplifier, cavity motors, oscillator motors, lase lock (note: there is an issue with the keyboard, we are not able to use it with remote access!!!!!!!!)

Note on Amplifier: On Friday, Daniele and Ronic faced again the temperature issue that came up before. it is due to the fluctuation of the diode temperature.

It was fixed today by Ronic and Daniele. it seems there are three diodes for monitoring the temperature, only one was connected, and it had issues, with some directions from alphanov. 

Ronic just removed the defective diode and soldered (connected) a different one. The amplifier should work without this issue. 

now we start searching for X-rays after locking the cavity remotely  

Last week, with Ronic and Victor we aligned the cavity using CW laser (Koheras)

• we have also installed 4 mirrors in the cavity with the best theoretical qualities (serial number and images included)
  • The Plan ULE mirror P4 thickness was not compatible with the piezoelectric mount. We had to install a metal spacer behind the mirror to be able to fix it. the metal spacers in from ThorLabs made from INOX, It is 1 inch diameter (25.4 mm), we drilled a hole in the middle of 15 mm in the Workshop in bat 200. Then cleaned it using an ultrasound bath in pure water, using a small Ultrasound bath machine in Maverics platform Vide and Surfaces next to ThomX eglo.
  •  
  • This gives some difficulties in imaging the transmission at P4. To help with the imaging, we used the plastic #D printed irises that Yann made long time ago
  • we took images of the mode inside the cavity at P4 transmission.

• We also observed some oxidization on the metal bars of the controllers, more on the side of S2 and P4. we are yet to test the motion of the motors in the z-axis.
• Friday evening we closed the windows using a new copper rings (last one we have, Ronic placed a new order).
• The pump was turned on by Bruno and Eric yesterday afternoon. The current vacuum level is 6-7*10^-6 mbar

the pre and the turbo pimps are on so still too noisy to work, we have access all day tomorrow.

Today, we prepared lenses for a telescope for the CW laser injection into the cavity, yet to be installed

Image of the transmission at P4 attached, an estimation of the beam size of the mode see is ~ 5.5 mm 

The vacuum in the 2 optical cavities is decreasing but slowly. today it is 2.6 - 2.4 * 10^-7 mbar

Yesterday morning we locked the cavity on a strange mode in the cavity (we call it mode, but not sure what it is ??)

we also managed to lock on a higher order mode 02

we get an estimated 30% coupling (expected value), and note that we have not installed a telescope yet.

This morning with Daniele and Viktor,

- we confirmed the "potato" mode was well centered on the injected beam and was not due to some misalignment of the injected beam compared to the cavity axis.
we look at the reflected beam during a lock. we can see the direct reflected beam superposed with the cavity mode (cf attached image).

- then we assumed the "potato" mode problem could come from the too short distance between spherical mirrors which introduces ellipticity and finally can lead to some instability.
we manage to move further spherical mirrors S2 and S3 by moving them from 1 350 000 to 800 000 steps.
=> we increased the distance by 2x 550 000 steps (with 6µm for 1000 steps) => we increased the distance between spherical mirrors by 6.6 mm
the new mode shrinked a lot and at the end was spherical at 73%.
the mode size is now about 4400 x 6000 µm but with the major and minor axis still at 45° !
 

This morning, with Ronic and Daniele, we locked the cavity again (The lock was relatively easy and stable during the reading of the finesse)

We took 2 reading of finesse

1st   : @ 33.2808 MHz (what the cavity length was at)           :  Finesse = 27 024

2nd :  @ 33.3382 MHz (adjusted to match the pulsed laser)  :  Finesse = 30 433

The difference between the 2 is the FSR, during the change we also did some alignment to counter the reduced transmitted power.

We took an image of the beam profile before and after changing FSR and there was ~ 70 um change in the beam position on the Horizontal axis of the beam.

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.

 

yesterday morning with Manar,

1) we fixed the threshold level of the laser input signal which makes the measurement of the repetition rate.
(if the rep rate is not measured properly, the amplifier safety interlock stops immediately the amplification).

we followed a tutorial from Guillaume Machinet.
when you start the Alphanov control software, 4 panels pops up : central control, 2nd stage amplifier, and 2 panels for controlling the pumps of the 3rd stage amplifier.
!!! Warning !!! ..... if you switch ON the amplifier using the central control panel, the amplifier starts immediately AT FULL POWER..... !!! Warning !!!
it is not mentionned in the tutorial document.
to prevent this problem, you first need to switch "Laser OFF" on the 2 panels controlling the pumps of the 3rd stage amplifier and let "Laser ON" only on the panel controlling the 2nd stage.

after starting the amplifier, we tried to find the median value of the threshold to get ~33MHz instead of 100MHz measured previously.
the initial voltage threshold on the photodiode measuring the rep rate was 0.4V which leads to get 100MHz.
first, we changed step by step the threshold to reach 0.87V => one gets 33MHz.
we tried the find the maximum threshold but once the level is above the signal maximum value, it triggers an alarm and stops immediately the amplifier.
then, one needs to restart completely the software which can be tedious due to connections/alarms issues.
finaly, we found out that the low and high level thresholds to get 33MHz were not reproductible at each start of the amplifier... :-(
then, we put the threshold at 1V following the turial procedure which seems to work.

2) we installed the optical scheme to make the beam profile measurement : see attached image
we used the HR mirror close to the amplifier output (as putting a wedge at that place is not convenient if you want to properly dump the transmission and reflections).
and then, we placed 2 wedges, using the front reflection to get low power beam profile.
the Thorlabs LB2 has been used to dump the transmission of the first wedge, it can handle 25kW/cm² and 25J/cm².
we used black aluminium screens to dump the secondary beams.
we measured after the 2 wedges :
amplifier at 20% => 71µW
amplifier at 30% => 139µW
amplifier at 40% => 200µW

it has to be compared with the amplifier power :
amplifier at 20%               =>               8.7 W
amplifier at 30%               =>               17 W
amplifier at 40%               =>               26 W

which leads to a reflection coefficient of the wedge of 0.28%.
=> OK, as one uses PS811-B Thorlabs 4° wedges with B coating.
with B coating, the reflectivity given by the manufacturer is around 0.3% @ 1030nm.

unfortunately, we had a "case temperature alarm" coming from the Alphanov software when we reached 40% for the amplification level.
this alarm stopped immediately the amplifier.
we saw that the chiller was in warning state too and the "present temperature PV" was not stable at all, flutuating by 3-4 degrees after the amplifier has been turned off...
we restarted several times the chiller to see if the problem disapears but it was still there ! => to be investiguated !

PS : we changed the USB cable between the amplifier controler and the PC to try to fix the several "connexion lost" problems but it didn't help...

PS2 : after discussing with Sophie Chance and Marie Jacquet, ThomX suffered a water circuit leakage on Monday:
the full circuit has been emptied and they had to remplace the water by some common water and not demineralized water....
it can be related to the chilller issue observed yesterday !

this morning with Manar,

- we checked first the chiller problem.
the fluctations of +/-2° around 25°C are still there.
I discussed with Jean-Noel Cayla about the possible problem of the "dirty" water in the primary circuit.
he told me that the water goes through 3 "effective" filters, then the water should not be too dirty in the primary circuit even if one uses "common water" to fill it.
he told me also that the water temperature could be a bit higher than before, around 22°C, and that could prevent a good thermal exchange with the secundary circuit (the one of the amplifier).
=> the resistivity is about 7Mohmhs.
we had again a "case temperature alarm" from the Alphanov Software, after 1h of work @ 20%
this stopped the amplifier, we did not restart it.

- we measured the beam path with the wedges :
compressor box output to mirror :    17cm
mirror to 1s wedge :                          24 cm
1st wedge to 2nd wedge :                 24.5 cm
2nd wedge to lift bottom mirror :       136 cm
lift bottom mirror to top mirror :          14 cm
lift top mirror to beam profiler (x=0) :   7 cm

- we measured the beam profile at 3 positions with amplifier @ 20% + 2 wedges :
the power is ~ 70 µW
we made the measurements at x=0, x=60 cm, x=120cm
after that, we had the Alphanov amplifier "temperature case incident" and we stopped the measurements.
 

Today with Ronic

For the Temperature fluctuation :

• we checked the valves of the tubes bumping water into the chiller from ThomX main water supply, they were working Ok
• we have also done "auto-tuning" of the chiller  
  If the controlled temperature fluctuates constantly after reaching the target temperature, perform auto-tuning . Controller calculates optimum control PID and set automatically.
   This function sets the values necessary for the control system such as PID (proportional band, integral time, derivative time and ratio of cooling/heating gain) automatically. 

after there was no temperature fluctuation and it was ok.

we turned on the amplifier @ 40 % amplification ~ 18 W , the error of temperature on the alphanov software satrted after 10 - 15 min

Then we turned it on @ 20% amplification ~ 9W, it showed after 5 min.

For the Beam profile measurement, we have a 750 mm lens to measure the M^2 and the beam divergence (to be finished!!)

Also installed an iris close the path to cut the bump beam when doing the measurements.

We checked the shape at closer distance similar to the one done on Monday (where the fit was not so good ~ 88%) and it is better, reaching 93% of Gaussian beam fit with the iris (being careful not to cut the beam power).

this morning with Manar,

- we fixed the chiller problem (+/-2°C fluctuation around the set temperature value = 25°C).
we opened and closed several times the water valve of the primary circuit to remove air bubles => no effect on the temperature variations.
we put the chiller in "Auto-Tuning" (AT) mode, then pressed the "AT" key => the chiller tune its PID parameters to optimize its temperature stabilization => no more fluctuations (+/-0.2°C fluctuation around the set temperature value = 25°C).
we had anyway a "temperature case" alarm from the Alphanov software at P=40%*Pmax, which stops the amplifier.
we put the chiller it AT mode again but with some power in the amplifier => no difference, the temperature regulation seems very good now, but we still have some "temperature case" alarms... => contact Alphanov for that.

- we changed the mount of the 2nd wedge by a kinematic mount to help for the alignment and we added an iris in the path.
now the optical path seems OK to make the beam profile measurement easily.
as we have still amplifier stops due to "temperature case" alarm, even at low power (P=20%*Pmax), we stopped the measurements => see Manar logbook post.

Ronic on Friday operated the Amplifier from the Alphanov software, switched it off then turned on the LAL software,

and it worked for 40 min without issues or error appearing,

the laser amplifier worked for some days but it ended to a "watchdog" alarm which switches off the amplifier... investigation is ongoing

we have had this new issue (watchdog alarm switching off the amplifier) for several days.

Alphanov mentionned it could come from the input oscillator stability (modelock loss for example).

Today,

- I tried to start the amplifier at 0% but it ended immediately in a "watchdog alarm" which stopped the amplifier
the input average power detected by the software was around 5.2mW, far above the 2mW needed by the amplifier.

- I checked the 33MHz oscillator at the output of the fiber connected to the Shafter-Kirchhoff fiber coupler with the Labbuddy fiber photodiode and a scope.
see the picture below : the peak are clean and at 33MHz... then, the Onefive oscillator is not faulty.

- after plugging back the fiber to the amplifier input, the input average power detected by the software increased a bit around 5.5 - 5.6mW.
I tried to start again the amplifier at 0% and now, it worked without any alarm !!!
then, the origin of the "watchdog alarm" was maybe the threshold on this input power.

Then, I launched the "Alphanov" software and changed again the "threshold level", previously set at 1V (see previous post below), to 0.96V !
with this threshold level, the Alphanov software detects at the beginning a frequency of 66MHz and then decreases slowly to 33MHz => to be understood.
it should allow also more room before triggering again the "watchdog alarm" if the input average power decreases a bit => to be confirmed by Alphanov.

With Daniele after, we took a readings of the beam with a lens of 750 mm.

From the observed data, we can state that the beam is not completely Gaussian M2 > 1, due to the variation of the ellipticity of the beam along the focused path 

readings have been saved and will be added after processing them.

Also adding to the previous comment about the error, after closing the bunker and starting the measurement we did not have issue for around 20 min then the same error appeared (alarm triggered by Watchdog) it shows when the input average power detected by the software was around 5.474 mW , I did a reset of the software then turned the amplifier on and the reading is 5.515mW it works for about 2 minutes (enough to take 2 readings) then it switches off. In addition, there was a drop in the power reading on the PD_preamp2 (which seems related to watchdog issue) we had to do this many times in order to finish taking the readings .

This morning,

- with the "Alphanov" software => Central panel => "system" button => Watchdog "Period Max" was at 100ns and has been set to 200ns.
(Alphanov told me to change the value from 50ns to 100ns but it was already at 100ns, then I set it to 200ns).
=> to be checked with Alphanov : what is the meaning of this parameter.

- it seems the watchdog alarm is related to the "PD_IN" parameter value of the "LAL" software (5.5mW is OK, but 5.2mW triggers the alarm).
my understanding is the Threshold Voltage, which detects the input signal to measure the repetition rate, could be at a too high level... even very close to the max level of the signal.
then if the input decreases a little bit, the signal goes below this Threshold Voltage => the software does not detect a signal any more => it triggers the watchdog alarm and the amplifier stops
(which stops also the preamplifier, related to the PD_CRI of the "Alphanov" software which goes to ~0W. PD_Preamp2 is a copy of PD_CRI but in the "LAL" software).

then, I changed back the Threshold Voltage from 0.96V (to detect properly 33MHz rep rate) to 0.7V which is close to the original value (0.67V) but for which the software detects ~100MHz rep. rate !
with this Threshold level, I did a test by detuning very slightly the input power by unscrewing a little bit the fiber-fiber coupler => PD_IN = 4.9mW => no alarm triggered !
then I screwed back the coupler => PD_IN = 5.6mW.

I did a power test with 3rd stage of the amplifier at 20% during 15 minutes => no alarm.

conclusion : there is an issue with the rep rate detection.
at 33MHz, one needs to put the threshold at the limit of the signal which fires an alarm if the signal decreased a little bit.
by lowering the threshold => no more alarm (I hope) but a wrong rep rate value !

This morning with Daniele, we did a second measurement of the beam profile using a different lens of focal 400 mm.

at a power amplification of 20%

the amplifier stayed on for around one hour and a half with no errors. 

tomorrow will attemt to do one at higher amplification percentage.

data will be added after processing.

On Monday 20th of February, Daniele and Viktor took some beam profile measurement data @ 50% of power amplification.

data and analysis can be found in the attached file.

This morning with Victor we took a reading of the beam profile using a 400 mm lens at 70 % and 100 % amplification.

Will process the data and add after

Note : after an hour and half of amplifier on at 70% we increased the power to 100%, and after ~ 10 minutes the amplifier turned off and showed an error on the software called MMD3

and an error of the power mentioning " Le laser a été arrêté parce que sa puissance est trop éloignée de la puissance nominale"

"The laser has been stopped because its power is too far from the nominal power"

after that, the amplifier worked in varying intervals until it switched off because of the previously mentioned error.

solution could be related to the configuration file values ??????

this morning with Manar,
we checked the Alphanov amplifier issue : "The laser has been stopped because its power is too far from the nominal power".

the photodiode voltage measuring the output power has drifted again and then, the estimated output power was wrong, triggering an alarm issue.
I changed the "calibration" file to fix the issue : see the attached file
 

We took reading of the beam profile of the amplifier without a lens @ 30 cm from the 2nd wedge for amplification percentages

20-30-40-50-60-70-80-90-100 % another additional 3 readings will be taken at different locations for all amplification percentages.

due to several "case temperature" issues, I change the "Max case temperature" in the "general config" of the "Alphanov Software" from 50°C to 55°C.
=> validated by Alphanov.

All the equipments have been switched off on Friday 17th due to a power shut down on Saturday 18th :
CW and Onefive oscillators, computers, laser amplifier, cavity mirror motors, chiller, etc...

Today, I restarted all the equipements :

Chiller                                                 : ok, temperature converged quickly to the set temperature : 25°C
Cavity mirrors motors controller         : I had to configure the general network as 192.168.xxx.xxx in order to operate the software designed by Didier Jehanno
Computer                                           : ok, now, it IP address is 192.168.1.1
Laser amplifier controller                    : I had a LOT of issues in restarting the LAL software. I had to restart several times the amplifier controller in order to access it by software. I quickly check the power increase to 50% after it has been correctly seeded
CW oscillator                                     : ok, Koheras restarted without any issue.
OneFive oscillator                             : the power ON was ok but it did not modelock. I tried several gently knocks on the case but without success (one clearly see the effect on the scope, the oscillator "tries" to modelock).
                                                            fortunately, after about 1h, the oscillator modelocked alone (check with Buddy fiber photodiode + scope).... the power is the same as before. the Alphanov software measures 5.4mW (it was 5.5 mW the 2/1/2023)

Smaract controller for OneFive        : ok, I changed its IP address to 192.168.1.10. I tested the PC control in moving forth and back the "CEP" motor by 1mm... the OneFive was still modelocked.
 

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.

As the general local network for the FP-cavity devices is 192.168.xxx.xxx, I changed the IP adress of the smaract laser motors (Frep and CEP) controller.

For that, I used the embedded web server as described in the manual in attached file.

the new adresses are :
IP :             192.168.1.10
Gateaway : 192.168.1.1
Subnet :      255.255.255.0
Port :          5000

Today we tested a mirror from one patch

image is for the front face of the mirror

PowerPoint has more details about the images

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, in order to prepare the installation of the news FP cavity mirrors,

- we installed the Koheras below the optical table
- we put a fiber prolongator at the end of the Koheras fiber and we put a mounted collimator at the end of the fiber.
we added a mirror at 45° to inject the beam to injection axis of the table.
- as the beam was still slightly divergent, we added a 750mm lens ~20cm after the collimator to improve the beam collimation.
now the collimated beam is going approximatively through the middle all of the iris in the optical path.

we finished by ~2h of cleaning of the optical table and elements, which were very dirty.
it is still a bit dirty. see the attached file to get the numbers provided by the particle counter after the cleaning.

This morning with Ronic , in preparation for the mirror installation, we removed additional mechanics and cables from the table. 

We organized and cleaned the permanently installed cables on the table away from the area of the cavity opening. 

We opened the two top vents and left the shutters open to circulate clean air , (note the shutters surrounding the laser and amplifier are half closed for safety)

Note: before installing the mirrors, preferably the shutters should be opened a day before to have clean air in the surrounding of the cavity openings

and avoid any cleaning or air disturbance.

Adding the schematic of the measurements.,

the 4° Beam Deviation, AR Coating ( B coating)

The 3 data points taken of the beam profile are fitted in Gaussian Beam with taking the beam waist at the output of the compressor box.

Background is subtracted for all data points, the fit is more than 90% for all points.

a reading was observed with distance less than 200 cm before the periscope and the fit starts to degrade

reason probably be related to the bump beam !!! To be investigated by placing an iris.

This Morning with Victor the amplifier was turned on @ 20% amplification (output ~ 9 W ) for approximately 3 hours and no error appeared.

I took data of the beam profile at different points without a lens after the 2 wedges 

@ 0% (only pump beam), output ~ 300 mW (taken from previous data) , output after 2 wedges 2.2 uW  

@ 20% amplification , output ~ 9 W (taken from previous data) , output after 2 wedges 58.6 uW

fit to be added after processing the Beam Profiles data files.

Data with the lens to be taken !!

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°.

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?
 

Today: Manar, Ronic and Aurlien started the study of the beam profile of the alphanov amplifier at high power.

The setup shown in the image shows how the power is reduced by using Anti-reflective mirrors,

pick up 1 : Anti-reflective coating on both sides , pick up 2 : Anti-reflective coating on one side and High reflectivity on the other

using this method, we avoid saturation and damage to the beam profiler from the high power amplified laser

in addition, an OD3 filter is placed in front of the beam profiler. and a reflective mirror is placed close to deflect the reflection from the mirror(pick up 1) second surface.

The beam observed is relatively well shaped and fitted up to 50% of amplification is where the shape starts to deform a little and is not well-fitted by a Gaussian. (image attached shows the fit for 60% amplification)

The cause is yet to be determined, as it could only be related to the reflections that occur from the mirrors (pick up 1 and pick up 2)

*** Note be always careful at High Power :)

Adding the fitted beam in 1D in Horizontal and vertical axis.

for 10%   to  60%

Today a second reading of the beam profile was done , with Victor ,Ronic, Aurlien and Manar

an additional set-up was made using two 4 deg wedges instead of High reflecting (HR) and Anti-reflecting (AR) mirrors.

Two reading were taken:

• at the output of the compressor with a NE30A filter on the beam profiler
• at the output of the amplifier with NE30A + NE10A filter on beam profiler

Readings of the beam shape and horizontal (upper plot) and vertical (lower plot) axis fit at the direct output of the amplifier.

The beam shape relatively shaped like an egg.

Readings of the beam shape and fit at the output of the compressor

differance from previous reading is that here we used wedges instead of HR mirrors.

Similar to previous readings, the beam shape deforms and the Gaussian fit is bad after 50% amplification

Adding the readings  20% , 30% ,  40%  for output of amplifier after the compressor

This Morning, another reading was taken for the output of the amplifier after the compressor using 2 wedge mirrors.

In addition, a start of the calibration of a PulseCheck "Autocorrelator" to measure the pulse duration. 

note, the pulsed laser used is OneFive 133.33 MHz

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.

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%

The pulse duration from the amplifier compressor output will be measured using PulseCheck autocorelator

a first alignment of the device was done, continuation in the afternoon.

YouTube link attached of the general operation of pulse check < 5 min :  https://www.youtube.com/watch?v=J1pNHYySSYg

Measurement of the pulse was done at the end of the afternoon, Pulse Duration FWHM = 12.9 ps

After a long process of adjusting the alignment and angle of the crystal inside the device

The power input on the PulseCheck device should be above the sensitivity, in our case we had 1 mW input.

To reach it, we removed one of the wedge mirrors and used dielectric mirrors with an amplification of 20% ~ 25 W direct output power.

The input to the pulsecheck must be horizontally polarized, which is why we used a polarizing beam splitter (PBS).

For a better pulse shape, Victor adjusted the "beam distance" and  "beam focus" nobs on the device.

Pulse Duration FWHM = 12.9 ps

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

Software Works well and is operational.

Just closing the log series!!!

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.