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.

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

Software Works well and is operational.

Just closing the log series!!!

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

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

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

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.

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

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

for 10%   to  60%

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 :)

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.

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.

Attached is the current setup in ThomX

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

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!

Updated beam image after change on the mode axis.

Taken after P4.

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.

one thing which could reduce the Finesse is the L-shape metal piece if it is slightly inserted in the FP-cavity mode path.
understanding where this L-shape effectively is is not easy... some pictures are attached.

After changing the way of injecting modulation for PDH and modulation for FSR scanning (we split the modulations to 2 different EOMs), the locking is very stable and we can measure the Finesse.

FSR = 33.34MHz

hereafter, the transmission power during an FSR scan and its fit (sweep of 300kHz of FSR in 2s)

we took 5 acquisitions which give a Finesse of :

4236
4254
4400
4045
4177

=> roughly Finesse = 4200 ! far from the 17000 previously obtained........