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

Today, the power measured at the input of the amplifier (PD_IN on the LAL amplifier software) is 2.5mW instead of >3mW generally measured

The power coming from the NKT/Onefive Origami oscillator is still >37mW (measured directly with the powermeter at the laser output without OD2).

thus, the problem should come from:

- the strecher/fiber alignment.

- or maybe from a wavelength shift of the oscillator

today, the Alphanov amplifier stopped because of the too low injected power : ~2.5mW (measured by the Alphanov software)
it was still working at ~2.7mW.
normally, the injected power is ~3.1mW (equivalent to 6.2mW measured directly at the fiber output).
I checked the power coming from the OneFive oscillator : it is still 36mW, identical to the power measured the first day we installed it.

by moving the "focus" knob of the mount, we saw this 3.1mW back but it was impossible to get it in a stable way.
so we think the "strecher box alignment" is still good and we decided to realign the Schafter-Kirchhoff fiber mount.

up to now, we lost all the coupling in the mount, then we improved the power at the fiber output to 4.2mW, then we lost everything again.
we will continue this afternoon.

this afternoon, I was able to go back to 5.4mW in the fiber output (3.2-3.3mW in the Alphanov software).
IN CASE OF SMALL LOSS OF POWER IN THE FIBER : DON'T TOUCH THE SCHAFTER-KIRCHHOFF MOUNT
it is too sensitive... open the Strecher box and do the alignment improvement with the 2 final (alignment) mirrors in the box.
even if it is mandatory to adjust the Schafter-Kirchhoff mount, you will have to finish the alignment with the 2 final (alignment) mirrors of the Strecher box.

Now, all the Schafter-Kirchhoff mount screws are well tighten !
So next time, use the Strecher box final mirrors to improve the injection into the fiber.

after the new fiber alignment, I was able to lock "as usual" the cavity to 47kW @30% of laser amplifier ratio.

The laser starts at 93 KW.

This morning I operated the laser locked with the RF for 1h30 without any delock. All the machine was switch off.

All the system was very stable. Sometimes the 20 Hz perturbation was visible but no delocking.

In the afternoon I switched ON just the kikers and septum (with the Kikers delay of not giving perturbation for the synchro -8.561) and I do the same thing => The situation is exactely the same, all the system is very stable (but 20 Hz perturbations). NO deloking during 1h.

I change the delay between Kikers to -7.561 => exactely the same situation, all is very stable!!!!

In 3h of synchronized operation, NO delock at all with or without Kikers!!!

Conclusion no effect at all when juste pulsed element are switched ON.

Daniele

Spin coater firstly needed vacuum and air supply. The air supply being useless for our experiments, it has been disabled.

The process is the following and is reversible:

1)            Remove the hub from the top of the spin coater, (see picture 1), 4 screws hold the hub in place, once these screws are removed the hub will lift off the motor shaft.
2)            Remove the 2 screws holding the stainless steel top decks in place (see picture 2), please be careful when removing the top deck as the lid switch wire will be attached.
Once these have been removed, you can access the inside of the spin coater.
You must add a bypass wire to the timing block (see picture Purge Bypass 1), the wire must be connected to the A1 and 28 ports on the timing block and remove the red wires from connexion. This will now cause the spin coater to bypass the purge check switch and allow the machine to boot up without air/nitrogen being supplied. To revert this change, simply remove the bypass wire you have installed and plug the 2 red wires back to A1 and 28.

The "enter" button of the front panel had some trouble and has been changed.

The spherical mirrors are at the closest position to get a FSR ~=33.3435 MHz. Planar mirrors are at the largest position.

The finesse has been measured about 17 000. 

Beam diameter (2*w) is ~= 4.6 mm x and y.

current Smaract motors parameters : 
- Closed loop Max frequency : 5000
- Signal Amplitude threshold : 2047
- High voltage threshold : 511

when one drives the Smaract motors in "closed loop" mode, one can get a displacement as small as 50nm... but at the price of a delock of the laser/FP-cavity.

when one drives the motor in "open loop" mode, 1 step is equivalent to 4µm !!! it is much larger than the laser PZT range.

when one drives the motor in "Piezo Scan" mode with a speed of 1V/s, one can move the motor without losing the laser/Fp-cavity lock.
the PZT voltage range of 100V (max value) is roughly equivalent to 2-3µm of round trip length, which is enough to manage several "fast" (10-20 minutes) oscillations of the laser frequency :
see these posts to get some info on the laser frequency oscillations : https://elog.lal.in2p3.fr/FPC/THOMX+commissioning/289

previously, we were using a spare Smaract MCS controller to drive the Onefive linear stages (without -LV -low vibration- option and using Ethernet),
during the repair of the initial MCS controller with -LV option.

this morning, it has been remplaced by the initial OEM Smaract  MCS controller integrated by Onefive (with -LV option and using USB).

it worked fine with the Precision Tool Commander 2 software !

today, the equivalent Smaract position corresponding to the 500.25MHz ring frequency is +156µm on MCS-1/ch0 (closed loop mode)

temperature stable around 20.8°C

today, the equivalent Smaract position corresponding to the 500.25MHz ring frequency is +158.4µm on MCS-1/ch0 (closed loop mode)

it is very difficult to maintain both loops in the same time as soon as it is needed to move one motor (CFP or Laser) because of the one element (RF reference or Laser or CFP) is drifting in frequency.

to try to understand why these 3 elements seems to drift so fast one from each other, we only measure the beating frequency between the RF reference and the free running laser (without lock of the CFP)... and we see a drift around several Hz by second of the beating signal => who is guilty ? Laser or RF synthesizer ?

one can compare their respective phase noise to have an idea of their relative phase/frequency stability :

the OneFive phase noise gives +40dBc/Hz  @10Hz offset in optical frequency which is 300000 (110dB) more than at 1GHz => 40 - 110 = -70dBc/Hz @10Hz offset @ 1GHz

to be compared to the SMA100A which gives -85dBc/Hz @10Hz offset @ 1GHz

conclusion : the RF reference should be more stable in long term and the drifts we see should come from the laser...

temperature stable around 21.7°C

today, the equivalent Smaract position corresponding to the 500.25MHz ring frequency is +147µm on MCS-1/ch0 (closed loop mode)

this morning, I plugged back the 4 power cables which supply all the equipments.

all the equipments have restarted without problem, but the shutter of the laser amplifier needs a ThomX safety system grant to let the beam propagate to the cavity...
and then continue the commissioning of the restart after Christmas shutdown.

the laser coupled into the amplifier is still measured at ~3mW at the input, on the Alphanov software, once the Amp stage are started at 0% of power ratio.

this afternoon, Kevin restarted the 3rd safety system of ThomX to grant the opening of the beam shutter => now the shutter can be opened.

after adjusting the phase for the PDH system, I was able to find back the laser/CFP lock.

after some minimal alignement, one gets back 50kW for 30.5% of laser amplifier ratio, as before the Christmas shutdown.

I didn't try to lock the FP cavity on the 500MHz RF reference clock as I'm not sure if it has been set to 500.25MHz (as before shutdown) or at 500.1MHz (the future RF frequency) which is very far and will require to move the FP cavity on a long rage.
=> I will ask to Vincent Chaumat to confirm the present RF frequency.

this morning, I set the Ring frequency at 500.25MHz and after switching ON the power supply of the amplifiers for the RF signal coming from the laser,
I saw the beating frequency  (between ring RF and laser harmonic frerquencies at 500.25MHz) that I canceled, playing with the Smaract motor.

Now, I need to adjust the FP-cavity length to follow the laser cavity length but the IcePap DS (controlling the FP-cavity motor) freezes too often and it is almost impossible to make the adjustment.
Kevin sent a GLPI ticket to try to solve this problem.... waiting for IT answer...

on last friday (12/01/2024), the IcePap DS issue was solved and I was able to control the FP-cavity motors properly.
I was able to quickly lock either the laser on the FP-cavity and the FP-cavity on the RF reference as before.

then, we can close these posts on restarting the equipments after the Christmas shutdown

this morning we locked the laser and the FP-cavity with ~ 40kW => some HOM appeared "randomly" depending on the power.

we tried to play manually on the L-shape arm :
- first, we moved horizontally to put the L-shape in the beam axis
at some point, we saw the power level divided by ~2, we stopped and came back to restore the full power.
- then, we tried to move vertically.
whatever the direction, we were not able to see a clear cut of the beam.
BUT "strangely", at some point, the PZT drift followed the direction of the motion and was not really depending on the "cooling" or "heating" process when the lock stops or restart.
"strangely" again, at the endpoint, the power dropped by ~20-30% after a delock but it was impossible to restore the power when we put the arm at the initial position.
=> we had to adjust the FP-cavity alignment to restore the power !!!
=> we had the feeling that moving the arm could have misalign the cavity axis !!! :-(
=> we have to discuss with Yann and get the CAD files of the cavity to have a better understanding...