The pump voltage has been increased few days ago when looking for a modlock of the laser.

The 33MHz Onefive output power is now 3.58mW with OD1 filter ==> ~36mW.

There are 2µW @ 1% coupling fiber with OD1 filter ==> ~20µW ==> 2mW @99% coupling fiber (2mW to the amplifier).

Onefive output power measured today. 3.52 mW with OD1 filter ==> ~35mW.

After turning on, one can see the 133.33MHz Onefive output power for ~40min with OD2 filter (~/20). So the real output power is ~57mW. A measurment over several days (15?) should come in few weeks.

The spectrum here has been taken one day after turning on the Onefive (see Fig. 133_spectrum_full and 133_spectrum). One can see the central wavelength of 1030.5 nm and a small peak at 1054nm (see Fig. 133_spectrum2).

1)  Note: The OneFive laser used for experimenting is the one for the  SBox

but, for now only this laser arrived from the company so we are doing tests (measuring the spectrometer and power ) on it inside the ThomX cavity clean room.

2)  on the RF - Analyzer the value of the laser repetition frequency is measured:

* 17/12/2020 (when first turning it on, the day before in the afternoon )  --->  133.330 700 MHz 

*  this day18/12/2020 (in the afternoon, after a full day to it being on)  ---->    133.330 840 MHz

they have a difference of 140 Hz this comes from normal thermal expansion inside the laser which is ok, as it changed over the course of a day of operating the laser.

3) the power meter is connected to the desktop in the ThomX cavity room and a TeamViewer application has been installed to observe the measurement over the period of several days mentioned (15?) remotely.

to access this you need to have an account on the application and allow your account to access it from the desktop.

for now, only Ronic and Manar has remote access. 

today, during an attempt in improving the CEP with the Smaract controller CH2, we lost the laser modelock.

at this point, we decided to reference the Smaract CH2 for CEP :
now, 0 mm is roughly the middle of the motor range.
the endpoints of the motor are : +/- 5.9 mm
once we found back the laser modelock, we searched for the region where the modelock was still effective : +/- 1.8 mm

one rotate a lambda/2 before a PBS and meausure the refected power:

Pmax=35.6 mW

Pmin=107 µW

Ellipticity ~ 3 per mille

Power during ~20h, power after turn on, spectrum image and excel datas, polarisation and pulse length.

Powermeter measurments were done with a /10 filter.. 3 mW means 30 mW

Important: Onefive does not automatically locks after being turned on.

Beam Size Onefive added

Oscillator randomly unmodelocked on 3rd july afternoon (during oscillator power measurement, maybe a reflection from the powermeter power filter ?)

Modelocked this afternoon by putting Onefive motor and phase at reference on the PTC software. 

On Friday 11th of October, due to the Yvette flooding, all the AC power of ThomX have been shut down.
After the shutdown, I had to restart the Onefive oscillator but the laser modelock was lost.
I had to do a step of 1mm at 10mm/s with the Smaract motor on the rep rate channel (CH1)

After the step, the laser was mode-locking again, and I put it back in the original position at a much lower speed, ~10µm/s, to prevent a new modelock loss.
the power detected by the laser amplifier software is still above 3mW! => OK

Surprisingly, the laser amplifier software is not able to detect the oscillator frequency.
hopefully, the internal photodiode of the oscillator is sent to the CH4 of the R&S scope (192.168.229.21)
and we measured a correct 30ns of period, corresponding to 33MHz.

Because all the safety procedures are not fulfilled, the laser amplifier is not granted to start.
Maybe it is the Reason for the lack of measurement => to be verified later
 

This morning, I verified the reason why the seeder frequency was not displayed on the amplifier software screen:

one needs to start the amplifier (even at 0%) to see the seeder frequency !!!
now, we have 33.371MHz as expected ! => OK

the last thing to do is to tune again the PDH demodulation frequency, as the generator has been shut off during the AC shut down.
 

After the new Yvette flooding of the last week and the consecutive AC-shut down, I restarted this morning the laser with the same procedure (step of 1mm at 10mm/s with the Smaract motor on the rep rate channel (CH1)).

now, we have again 33.371MHz and 3.1mW input power as expected ! => OK

the last thing to do is to tune again the PDH demodulation frequency, as the generator has been shut off during the AC shut down.

For the modulation/demodulation generator for the PDH signal,
after a power shutdown, on can :
1) restart the generator to get the correct parameters:
CH1:3Vrms on 50 ohms @ 8.4MHz (demod)
CH2: 100mVrms on 50 ohms @ 8.4MHz (modulation on EOM)

2) do an "Align phase" on the generator

3) put 270° on CH2 (0° on CH1) to get the max Error signal
and use a "positive" sign on the Laselock : cf https://elog.lal.in2p3.fr/FPC/THOMX+commissioning/365

since several days, we see that the locking is more and more unstable and the lock duration was sometime less than 20-30 seconds !

1) I tried to optimize the feedback loops

I discovered that the gain on the fast loop on the laser EOM was very low and was almost uneffective for the global stability of the lock (I can remove the cable of the HV to EOM and it does not change the stability of the signals).
when I tried to increase this loop gain in open loop for the PZT loop, I clearly saw an improvement of the transmission signal stored in the cavity.
but when I close the PZT loop, it does not help to get a better locking.
so, at the end, I cancel this loop gain (HV amplifier for the EOM is OFF !) and only the slow feedback loop on the PZT is working.

I reduced the by a factor 2 the range on the PZT loop side to reduce the noise due to the amplified Laselock (voltage divider 1/2 before the HV amp for the PZT).
and I switched off the laser motor controller (Smaract MCS).
after optmization of the PID parameters, I was able to get back the 90kW we had in the past for 33% laser amp ratio and with a very good stability :
the transmission signal is a line and the reflection signal is almost a line too.
in this condition, I seems that I can lock the laser and the FPC indefinitely.

2) issue with Smaract controller

I put back the Smaract controller only for the CEP channel => one can clearly see a bit more noise on the PDH signal but the transmssion and the reflection signal stay almost the same with a very good stability.

then, I put back the Smaract controller for both channels (CEP and laser cavity length) => the lock was very bad, even after a PID optimization despite the fact it was a "Low Vibration" (LV) Smaract MCS controller.

we tried to change the 3-channels LV controller by a standard 3-channels (not LV) spare controller => it was OK for the CEP channel but not good at all the laser cavity length channel => very noisy.
so, we kept this standard controller for the CEP channel and we took 1-channel LV spare controller for the laser cavity length channel => it was ok. no more additionnal noise and we can work without delock in piezo-scan mode.

important parameters :
I used 1ms for hold time in the Smaract controller configuration.
I used 1V/s in piezo scan mode for the speed => it does affect the noise level when the piezo is moved !

3) IP Smaract controller parameters :

I used the MCSNetworkInterfaceConfig.exe software to configure both IP addresses of the 2 controllers.
it's easy, one just has to choose the options.

the IP address for controller ruling the laser cavity length is : 192.168.1.200:5000
the IP address for controller ruling the CEP is : 192.168.1.201:5000

4) final long run test

We did a 1/2h run test to check how many lock loss one gets... see the picture.
we had some few lock losses (with the RF feedback lock ON too) but most of the time, the RF phase was not lost and the X-rays should be continued to be produced.
a test should be done tomorrow.

yesterday, in the same conditions, we had so many locking issues... exactly in the same way than before. :-(
so we still have "locking issues" depending on something we didn't find...

today, we removed the "1/2 voltage divider" before the PZT amplifier to get back the full dynamic.
we have a little bit more noise and we lose some power on transmission (85kW instead of 90kW) but it worked pretty well.
we had quite long X-rays runs ~ 20 minutes without any lock losses => see the picture.

but we have to keep in mind that maybe it was just a "good" day and an another day can be "bad".
we still have to understand where do these perturbations come from.

the good news is we brought back the previous setting of the FPC.

With optical attenuation + x3 amplifier on laser PZT channel + feedback tuning

Temporary recipie for  ~ 92kW power in the FP-cavity:
(in the previous scheme, without x3 laser PZT amp, a good lock was achieved for a PDH signal power noise ~ 70 mV rms)

• Alplhanov amplifier ratio : 34%
   
• Axis 18 position : +0016956 steps
   
• PID A (for laser/FPC lock) :

input : input a
P = 0.04
I = 0.0005
D = 0.48
Sign : positive
Sampling : fast
filter : off

• Search A :

criterion : input d
upper th. : 10V
lower th. : 0.03V
speed : 100V/s
relock mode : none
off mode : reset

• Output A :

range : 50%
offset : 5V

• PID B (for RF/FPC lock) :

input : input b
P = 1
I = 0.00005
D = 1
Sign : positive
Sampling : mid
filter : off

• Search B :

criterion : input c
upper th. : +0.4V
lower th. : -0.45V
speed : 1V/s
relock mode : none
off mode : reset

• Output B :

range : 50%
offset : 5V

With optical attenuation only

For ~ 92kW power in the FP-cavity:

• Alplhanov amplifier ratio : 33%
   
• Axis 18 position : +0003768 steps
   
• PID A (for laser/FPC lock) :

input : input a
P = 0.1
I = 0.0015
D = 1.5
Sign : positive
Sampling : fast
filter : off

• Search A :

criterion : input d
upper th. : 10V
lower th. : 0.05V
speed : 100V/s
relock mode : none
off mode : hold

• Output A :

range : 50%
offset : 5V

• PID B (for RF/FPC lock) :

input : input b
P = 5
I = 0.0001
D = 1
Sign : negative
Sampling : mid
filter : off

• Search B :

criterion : input c
upper th. : 0.45V
lower th. : -0.45V
speed : 1V/s
relock mode : none
off mode : hold

• Output B :

range : 20%
offset : 5V

today, we were able to store more than 93kW in the FP cavity, always with the same parameter : 33% laser amplifier ratio

today, we were able to store more than 94kW in the FP cavity, always with the same parameter : 33% laser amplifier ratio

today, we were able to store more than 95kW in the FP cavity, always with the same parameter : 33% laser amplifier ratio