ELOG THOMX commissioning

lock oscillateur 33MHz - synthé 500MHz

Optical room

This morning with Daniele, we changed the laser/RF locking scheme :

1) we use the laser 33MHz internal photodiode to do some beating with the 33MHz RF generator (A Rigol generator locked on the 500MHz Ring oscillator).
this beating is only for monitoring purpose, in order to manually adjust the laser frequency at the beginning of a run.

2) the previous scheme was using a fast photodiode in reflection of the FP cavity to do some beating with the 500MHz Ring RF generator,
but the beating signal was becoming very noisy when the FP-cavity was locked.

so, we moved this fast photodiode in transmission of the FP-cavity, in addition to the slow one (already connected to the scope to monitor the transmitted power).
this fast photodiode is used to extract the 500MHz harmonics to make the beating with the 500MHz Ring RF generator.

now, this beating signal is very clean when the FP-cavity is locked (no signal when the FP-cavity is not locked, obviously).

=> the acquisition of the lock of the 2 feedback loops seems much more easy and stable.
BUT we did a jitter measurement and it is still around 10-15ps rms and seems to be dominated by the 20Hz noise oscillation !!!

some previous measurements showed that this oscillation should come from the laser or from the Alphanov amplifier (not from the FP-cavity).
we have to redo a beating test with the Alphanov amplifier @ 500MHz and with the laser @ 33MHz...

Ronic Chiche wrote:

after a sudden FP-cavity Finesse increase, we had to install the Fast Feedback Loop in order to continue to lock the cavity.

this afternoon, I was able to lock both the FP-cavity and the Laser on the 500.25MHz oscillator reference.

I had to change the CEP to reduce the effective Finesse and help to get a better stabililty => P ~ 25kW inside the FP-cavity for 30% of laser amp. power ratio.

the 20Hz oscillation is still there on the PZT signal and can be seen also on the reflected signal when the amplitude of the PZT signal is large or when the lock is lost or almost lost.
this 20Hz signal is modulated by a higher frequency of the reflected signal => to be investigated...

the posts, specific to the 20Hz oscillation noise, are here : https://elog.lal.in2p3.fr/FPC/THOMX+commissioning/258

this post closes this thread.

Ronic Chiche wrote:

this afternoon, we were able to lock the laser on the FP-cavity and the FP-cavity on the Ring reference oscillator in a same time from the control room.

the procedure when laser, cavity and reference oscillators are far in frequency, is :
1) start the amplifier to get the laser signal in the reference photodiode used to measure the 33MHz.
2) look at the beating frequency with the reference oscillator and quickly cancel it using the Smaract motors.
one need to remember the direction and distance corrected by the Smaract motors.
3) compensate the motion in the FP-cavity using these rules :
- 600nm with the Smaract motors <=> 100 steps on the FP-cavity motors
- decreasing the value on the Smaract motors <=> increasing the value on the FP-cavity motors
4) start the lock between the laser and FP-cavity
5) adjust both cavity length step by step until reaching < 5Hz of beating
6) start the lock between FP-cavity and reference oscillator

we still see the 20Hz noise both in the PDH error signal and in the laser PZT feedback signal.
it could mean :
either the FP cavity is stable but the Laser cavity is oscillating (noise source) and badly compensated by its own PZT
or the FP cavity is oscillating (noise source) and the Laser cavity is oscillating too (due to feedback) but badly compensated with the laser PZT
the bad compensation in both case could come from a mechanical resonance which produces a phase jump that the PID is not able to properly compensate, even with a high gain (integration).
=> to be checked with a behavorial simulation
the noise source in the laser cavity could be the Smaract motors.
=> we need to switch them off to compare the noise with and without

Ronic Chiche wrote:

this afternoon, I firstly connected the HV output of the Laselock to the FP-cavity PZT : https://elog.lal.in2p3.fr/FPC/THOMX+commissioning/248

locking the FP-cavity on the local synthesizer works better with the improved HV output range.
the ~20Hz oscillation in the beating signal of the FP-cavity/synthesizer is still there.
one can observe exactly the same oscillation on the Laser PZT signal.
I think the FP-cavity is oscillating at this frequency and the laser PZT correction signal is compensating it.
this oscillation produces also an error signal with the beating of the laser harmonic and the synthesizer.
an other possibility for this low frequency oscillation could be the hexapod stability ?

then, I switched to the 500MHz Ring Synthesizer instead of the local one.
we were able to lock all the elements, FP-cavity and Laser, in a same time.
we have Vp=3.25V of signal amplitude when not locked and dVrms = 140mVrms of rms noise once locked => rms jitter = dVrms / (2pi F Vp) ~ 13.7ps rms
with F=500MHz.

reaching a state where both loops are locked is not simple as :
- the FP-cavity motors are noisy when they move, and one direction has some backlash compensation which produces a long unlock.
- the laser motors are less noisy but too noisy to be moved w/o unlock
- moving the FP-cavity motor changes the laser PZT position and can put the system out of the locking range for the laser PZT.

the correct strategy is :
1) lock the laser on the FP-cavity using the laser motors (no lock of the FP-cavity compare to the synthesizer).
2) wait to have a quite good thermal stabilization => this can take time especially if it is the first lock of the day when the cavity is cold.
3) measure the frequency beating between FP-cavity and synthesizer.
4) pre-compensate the direction of the laser PZT with the laser motor when you will play on the FP-cavity motor
ex : a step on the right on P4 motor will move the laser PZT to the top, then you need to pre-compensate this move by placing the laser PZT voltage lower with the laser motor (Smaract).
5) do the move on P4 motor
6) check that the frequency beating between FP-cavity and synthesizer is reduced
7) redo 4) 5) 6) until the frequency beating is < 5Hz and stable
8) start the lock on the FP-cavity PZT.

due to the power drifts inducing frequency drifts, it will be difficult to work continuously more than a couple of minutes.
the procedure has to be done continously from 4) to 8)

having HV output on the laser PZT should help to improve both lockings range and inscrease the locking duration => to be checked w/o fast feedback loop (FFL) or with FFL if needed.

Ronic Chiche wrote:

this morning, I added a Thorlabs lowpass filter at 1kHz after the mixer and a resistor at the Laselock output to the FP-cavity PZT.
I set the PID with P=10 and I=D~0

in attachement, a plot of the 500MHz mixer output, before and during the lock.
during the lock, one gets a residual oscillation around 20Hz... where does it come from ???
could it be some mechanical resonance, as we already had before (it was ~30Hz) : https://elog.lal.in2p3.fr/FPC/THOMX+commissioning/84

when unlocked, one gets : A*sin(dPHI) with A=3V => 6Vpp signal
when locked, one gets a 400mVpp error signal => A*dPHIpp = 0.4pp => dPHIpp = 133 mrad

dPHI = 2*pi*F500M*dt => peak-peak jitter dtpp = 42 ps => rms jitter = 15ps

this value can be measured directly on the 500MHz signals coming from the laser and the reference synthesizer.

Ronic Chiche wrote:

this afternoon, I tried to lock the FP-cavity on a local 500MHz synthesizer as a frequency reference
(it's faster to change the frequency from the sythesizer than from the FP cavity !!!)

I found some parameters on the PID of the Laselock to phase-lock the reference and the FP-cavity
but the locking quality is poor => we produce some oscillations which are copied by the FP-cavity/laser lock on the laser PZT.

the error signal (FP-cavity/reference) is quite noisy, then maybe one can try to do some analog filtering at a lower frequency ?
=> one can use Thorlabs LPF at 10kHz or 1KHz.
one can try also to filter the signal going to the PZT to reduce the excitation of the PZT resonance.
=> use a variable resistor in serie with the PZT capacitance to make and RC filter (Cpzt ~ 70nF)

for reminding, the previously working PID parameters, found with the 133MHz laser/533MHz reference lock, were:
P=10, I=0.01, D=0 for mid SR, and no filtering.

once we will found good PID parameters, we will be able to switch to the Ring oscillator at 500MHz as a reference,
then work with HV from the Laselock to improve the locking range.

Ronic Chiche wrote:

this afternoon, I installed the frequency detection scheme in the bunker :

- I changed the large reflected photodiode DET100 by a fast small DET10.

- a 50ohms splitter is connected to the photodiode :

* one cable is going directly to the scope for monitoring
* one cable is going to the 500MHz sharp bandpass filter to select only this harmonic.
despite the small BW of the filter, one gets 3 harmonics : 500MHz + (0 +/- 33) MHz with a bit less power on sidebands.
power on 500MHz : ~ -30dBm if the laser amplifier is at 30%

- after the BPF, one goes directly to the RF amplifier which is 2x Minicircuit amp ZX60-33LN in cascade to get ~ +3dBm

- then one goes to the level 17 mixer on the RF port.
the LO port is feeded with the 500MHz coming from the Ring reference oscillator.

in attachement is a picture of the output signal : ~ 1.5Vpp
I think the width of the signal is coming from the 33MHz sidebands which are not perfectly removed by the 20MHz BW of the scope.
one finds a frequency shift of 250kHz.
as the laser frequency has been set at 500.25MHz (on the 15th harmonic), would it mean the Ring reference oscillator was at 500MHz sharp ? => to be checked with Kevin.

Ronic Chiche wrote:

Today, I connected the BNC-DB9 female prolongator cable to the FP-cavity PZT cable (DB9-DB9) and to the channel B of the Laselock.

I additionnaly connected the reflected laser beam (normally connected to scope ch2) to the spectrum analyzer @ 1GHz to observe the 30th harmonic of the laser comb.
on the 2 attached pictures, the 1st one is @0V on FP-cavity PZT and the 2nd one is @10V on the FP-cavity PZT.
as the laser is locked on the FP-cavity, its frequency follows the FP-cavity length and its frequency changes.

as expected, applying 10V on the FP-cavity PZT, increases the laser harmonic frequency @ 1GHz by about 10Hz => the relative change is 10^-9 V^-1
(as the FP-cavity length is always moving due to temperature or low frequency vibrations, there are always some FP-cavity length fluctuations, and the measurement has to be quick to get a correct evaluation).

Ronic Chiche wrote:

Today, I installed a DB9-DB9 female-male cable on the PZT connector of the FP-cavity.
the PZT is connected between pins 1 and 2, with a capacitance around 70nF.
I need to make a prolongator cable BNC-DB9 female to connect it to the feedback system.

with a (dLpzt / dV) of 5nm/V, one should be able to see 37mHz/V on Frep which is equivalent to ~10Hz/10V @ 1GHz (30th Frep harmonics)
I connected a photodiode on the spectrum analyzer to measure this variation => to be done tomorrow.

I don't have any information about the polarity of the PZT on the DB9 connector but I know that the PZT length should increase with positivite voltage in normal operation.
from the Yann documentation about the PZT mount (in attached file), it should mean that the cavity length should decrease when the PZT length is increasing, and then the FP-cavity FSR should increase.
=> to be tested tomorrow.

about the PZT mount :
I understand that the HR face of the P4 mirror is the face placed on the only part with a chamfer (chanfrein), on the FP-cavity side.
in the documentation, the PZT connector orientation is misleading as it is oriented to the FP-cavity side instead of to the "outside" as one can see it in the cavity picture in attached file.

Ronic Chiche wrote:

régler le problème 1:
Kevin m'a apporté un déphaseur Minicircuits JSPHS-661 (400-660MHz / 180° de phase) qui permet de déphaser le 500MHz de ~ 1ns avec une tension DC 0-10V.
on peut alors changer le signe du lock pour scanner les 2ns d'une période complète de 500MHz.
régler le problème 2:
la synchro anneau se fait sur la RF du synthé 500MHz avec une signal de trig fabriqué à partir d'un 16MHz, issu d'une division de ce 500MHz.
en cas de perte de synchro de la cavité FP, on va relocker sur le 500MHz mais avec une phase aléatoire par rapport au 16MHz.
on peut donc remplacer ce 16MHz par le signal 33MHz issu du laser de telle façon que l'injection des électrons dans l'anneau se fera toujours avec la même phase par rapport à ce signal à 33MHz.
il faudra donc envoyer ce signal issu du laser cavité FP au système de synchro anneau, de cette façon la phase d'injection des électrons dans l'anneau par rapport au laser sera toujours la même.
mais il n'y a aucune raison que les électrons tombent exactement sur le pulse laser (avec la bonne phase).
il faudra donc scanner la phase du signal de trig pour décaler l'injection machine par rapport au signal 33MHz avec des steps ~ 1ns.
pour cela, on peut utiliser les générateurs de delais Greenfield Technology GFT1020 actuellement utilisés pour la synchro (résolution 100ps).

voir schéma attaché en pdf

Ronic Chiche wrote:

pour préparer le lock cavité-anneau, j'ai un setup de lock en salle optique entre le laser OneFive 133MHz et un synthé à 533MHz (133MHz x4).
ce matin, j'ai pu locker les 2 ensembles avec le laselock avec une stabilité RMS, je pense inférieure à la ps.
ma limite de mesure du jitter temporel au scope est de ~ 2.5ps.

une fois locké avec le laselock, je peux facilement décaler légèrement en phase les 2 signaux de façon très précise (<1ps) en jouant sur l'offset de lock,
mais je ai une plage assez petite (+/- 250ps) qui correspond grosso modo aux plages linéaires du sinus (1/4 de période) soit 500ps (F ~ 533MHz => T ~ 2ns)
en changeant le signe du lock, je peux faire des sauts du lock d'une 1/2 période, soit 1ns...
mais cela ne suffit pas à couvrir l'intégralité de la période du signal de référence.

=> 1er problème : je n'ai accès qu'aux plages "linéaires" du signal de référence.
il faudrait un petit déphaseur programmable piloté en remote pour faire des steps de 100ps environ, sur une plage de 1 ou 2ns afin d'être sur de scanner tout la période du 500MHz.

en coupant le lock, les fréquences driftent l'une par rapport à l'autre.
et en raccrochant le lock, on peut scanner toute la période entre 2 pulses d'électrons par steps de 2ns.
puis en changeant le signe du lock, par steps de 2ns mais décalé de 1ns.
on peut donc facilement scanner la période des électrons avec des steps de 1ns et une plage de 500ps autour de chacun de ces steps.

=> 2e problème : lorsque l'on perd le lock de la cavité FP/laser involontairement, on perd l'info de la longueur de la cavité FP.
et lorsqu'on retrouvera le lock, il va se raccrocher sur une autre oscillation du 500MHz.
et donc on va perdre la phase avec les électrons à 16MHz.
=> on peut éventuellement afficher ce signal à 16MHz, en même temps que le 500MHz pour rechercher l'oscillation correspondante à la bonne phase sur le 16MHz.
mais dans tous les cas, il faudra rechercher à nouveau la phase é-/laser à chaque délock.

Autre possibilité, faire la synchro sur le 16MHz au lieu du 500MHz.
la tentative aujourd'hui n'a rien donné car le signal est 30x moins intense => beaucoup plus de bruit.
=> le lock n'arrive pas du tout à accrocher même en filtrant énormément le signal IF avec 10kHz de BW.

322

Fri Feb 2 11:53:40 2024

mechanics | lasers and optics

Laser cavity temperature/pressure sensitivity

this morning, I did a 500MHz beating frequency (Laser vs RF) drift test with the Smaract motors configured with "Sensor Mode" OFF over 50 minutes (~ 1500 acquisitions)

compared with previous measurements, one observes a much more smooth "exponential-like" drift compared to "Sensor Mode" ON (see previous posts).

Ronic Chiche wrote:

long-term correlation, over 5-6 days, between the temperature measured in the bunker, outside of the housing (blue curve) and the temperature measured with a probe stuck on the laser housing, inside of the FP-cavity housing (green).

it's a perfect correlation with almost the same temperature scale : 1°C outisde the housing => 1°C of laser housing

thus, a stabilization of the temperature, inside of the housing, could help to reduce the frequency drifts of the laser.

Ronic Chiche wrote:

today, I swapped the 500MHz RF reference oscillator for a Siglent 500MHz DDS oscillator.

see the attached plot : the beating frequency with the 500MHz laser harmonics produces the same behavior as before.
so, the oscillations should come from the laser temperature regulation.

Ronic Chiche wrote:

the last thing we did with Daniele, is to start/stop the airflow on top of the housing (closed) to see a possible pressure effect on the laser frequency drift.

fig 1 : in green, the temperature measured with the probe stuck on the laser housing.
one can clearly see the 2 "start - wait ~10mins - stop" we did at 16h50 then at 17h30.
the air temperature blowed by the airflow is cooler than the housing temperature and we see the effect on the probe.

fig 2 : this is the laser frequency drift during the 1st airflow start/stop
the airflow has been turned on at 100 iterations and stopped at 500 iterations (~5 mins)
we don't see any correlation

fig 3 : this is again the laser frequency drift during the 2nd airflow start/stop
the airflow has been turned on at 1850 iterations and stopped at 2550 iterations (~10 mins)
we don't see any correlation

CONCLUSION : neither external temperature change or pressure variations can explain the 10-20min period oscillations observed on the laser frequency variations.
it can be either the laser temperature regulation or the RF reference oscillator temperature regulation (due to the oven of the quartz)

Ronic Chiche wrote:

Now, I placed a temperature probe stuck on the laser housing itself.

fig. 1

one can compare the temperature measured at the surface of the laser housing and the beating frequency with the 500MHz reference oscillator
one sees a possible very long term correlation but there is no correlation at the minute level when we see the frequency oscillation after t=2000s.

the laser housing temperature seems not to induce directly a frequency variation.

fig 2 / 3

we applied 15W on the heating wire rolled around the FP-cavity flange.
in red, we see the temperature increasing on the probe rolled around the wire, reaching almost 30°C.
we heat the inside of the housing (airflow stopped) during more than 30 minutes
in green, we don't see any variation (even if one makes a zoom) of the temperature of the probe stuck on the laser housing.

in same time, on fig 3, one can see the frequency drift.
there is no correlation between the oscillations and the temperature.

CONCLUSION :
the laser frequency fluctuations does not seem to come from the outside temperature.

Ronic Chiche wrote:

laser cavity :

when one decreases the laser motor position, the laser repetition rate increases (laser cavity length decreases).
=> +/- laser motor step => +/- laser cavity roundtrip length => -/+ laser repetition rate => -/+ laser harmonic @500MHz
=> +/- 100nm => +/- 200nm => -/+ 0.7Hz @33.33MHz => -/+ 10Hz @500MHz

here is the natural variation of the laser cavity frequency beating with RF @500MHz over 1h (~1.6s / iteration)
one can see some oscillations equivalent to ~1µm of roundtrip length with ~10 minutes period and maybe a slower drift or oscillation with ~2µm of roundtrip range over the hour.
I mention that I moved the laser "PZT" motor before taking the data : could it be the reason of the 10-20min oscillations ?

during the same time, here is a probe temperature curve (the probe in stuck on the end flange, close to X-hutch, of the FP-cavity, inside the housing... not close to the laser position).
the temperature variation range is ~2.5/100 °C which induces on inox (relative length thermal effect : 17e-6 /K) a length variation of 4µm of roundtrip (10m) which could be compatible to the laser cavity length variation measured.

321

Thu Feb 1 17:23:23 2024

locking

during the last days we changed the FP-cavity - RF reference locking system to force the right bucket:
in addition to the 500MHz beating which is the signal input to the PID, we added a 33MHz beating signal which is the trigger signal of the PID.
then, the lock is triggered only when this trigger signal is close to 0.

as the peak input signal is Ap = 0.5V, the beating signal is Ap*sin(phi)
one needs a phi determination below 2pi/15 which correspond to a particular 500MHz bucket (500MHz/33MHz = 15).

so, Ap*sin(+/- 2pi/30) = +/- 0.2*Ap = +/- 0.1V
we should be able to put a trigger intervalle value between -0.1V and +0.1V to always fall into the same bucket.
we did a test with -0.05V et +0.05V and we always fall into the same bucket => we will have to test the intervalle -0.1V / +0.1V to check if it is ok or not.

as the crossing is around 0V, there is 2 possible locking trigger phase position with Pi intervalle.
for the moment, there is no way to get rid of this problem. one can only let the phase drift until it reaches the right phase to start the lock.

if one tries to detect the maximum or minimum value to fall into the same bucket, the voltage level is very sensitive :
Ap*sin(pi/2 +/- pi/30) = 0.995 * Ap => it has to be sensitive at 0.5% !

we changed also some locking condition on the 2 Laselock PID regulators : see the attached picture.
search and relock : reset mode with 0V for both => when the 2 PID are losing the lock, they search a new lock starting with the same 0V value on the PZT (it can prevent they are out of range in some cases)
with these condition, it seems the lock is quicker to come back.

we can check the phase bucket with the remote oscilloscope at the IP address : 192.168.229.21 (see attached picture)
blue : trigger signal @ 10Hz (will be 50Hz in next ThomX update)
red : reference 33MHz signal, phase linked with the 500MHz of the ring
yellow : laser 33MHz signal (need to have always the same phase relation with the reference 33MHz when locked to RF reference)

the rms jitter with the RF reference is still ~15ps => to be improved...

320

Fri Jan 26 13:04:56 2024

lasers and optics | detectors and electronics

33MHz (FP-cavity vs RF) phase stability

today, I locked the laser on the FP-cavity and the FP-cavity on the RF reference with 47kW inside the FP-cavity.

equivalent jitter :

when lock is OFF : sine signal V=V0*sin(phi(t)) with V0=300mV => Vrms = 300/sqrt(2)) = 210mV rms

when lock is ON : noise 10mV < dV < 20mV
for low phase values : dV=V0*dphi

when the RF locking is done, this voltage is about dV = 20mV rms => dphi = dV/V0 = 67 mrad
dphi = 2*pi*f0*dt => jitter dt = dphi/(2*pi*f0) = dV * T0/(2*pi*V0)

T0/(2*pi*V0) ~ 1ps/mV => jitter ~ 10-20 ps rms

previous measurements were exhibiting a jitter lower than 5ps rms : https://elog.lal.in2p3.fr/FPC/THOMX+commissioning/299

Ronic Chiche wrote:

this morning, with Vincent Chaumat, we made a beating (phase detection) between the laser 33MHz and the 33MHz coming from the Rigol generator locked by the 10MHz link onto the 500MHz ring generator.

once the laser and the FP-cavity are locked on the RF reference, the 33MHz phase detection is stabilized and confirm the laser/FP-cavity lock on the RF reference.

we plan to make a drift measurement and a jitter measurement to estimate this lock quality.
the 33MHz frequency being quite small, the quality of this estimation will be poor but it can give a "worse case" estimation.

319

Fri Jan 26 11:05:27 2024

mechanics | lasers and optics | cabling

controller M1 & M4 (plan mirrors) with IcePap controllers

at the begining of each session, it will be mandatory to avoid any backlash for the motors :

- for the P4 motor : one can go 2k steps DOWN, then 2k steps UP to go back to -360 000 and use the steps UP without any backlash
- for the P1 motor : one can go 2k steps UP, then 2k steps DOWN to go back to -900 000 and use the steps DOWN without any backlash

today, I used the P1 motor to do some steps DOWN to find back the main resonance at the begining of the session.

Ronic Chiche wrote:

this double motors scheme works good.

if motor P4 is used by increasing value, the FP-cavityPZT signal (pink signal on scope) goes HIGHER
if motor P1 is used by increasing value, the FP-cavityPZT signal (pink signal on scope) goes LOWER

!!! CAREFUL !!!
after each session, it is mandatory to put the motors back to their initial position to avoid FP-cavity misalignment.
on P1 : - 900 000 steps
on P4 : - 360 000 steps

Ronic Chiche wrote:

previously, we have connected motor M4 with an IcePap controller.
see this post : https://elog.lal.in2p3.fr/FPC/THOMX+commissioning/278

due to the backlash behavior of the FP-cavity motors, it is impossible to work in both directions on one motor when the FP-cavity is locked.
so, we decided to use also the motor M1 to work in the other direction.
then, normally M1 will work in one direction and M4 in the other direction.

motor M1 (or P1Z) which was on the axis 9 on the ISP controller has been assigned to OC/OP/OCH.01-MOT.06

motor M4 (or P4Z) which was on the axis 12 on the ISP controller has been assigned to OC/OP/OCH.01-MOT.03

318

Thu Jan 25 13:36:35 2024

First stable X-rays production

this morning, we locked the laser on the FP-cavity with about 48-49kW stable in the FP-cavity (for 32% of amplifier ratio).
and then we locked the FP-cavity on the RF reference (500MHz beating lock + 33MHz beating for starting lock search).

the starting lock search voltage has been chosen between -20mV and +20mV.

then we lock with an uncertainty of 180°... but we can check the lock phase with the "Synchro oscilloscope" (192.168.229.21).
if necessary, we can stop the lock and let the phase drift and then relock with the right phase.

Kevin did a buckets scan (30ns by 2ns steps) to find the right bucket and also a fine phase tuning scan (2ns scan).
unfortunately, the fine phase was close to 0, so the Laselock did the fine phase adjustement by changing the SetPoint of the RF loop to : -720mV

at this moment, we got relatively stable X-rays at an approximated flux of 1e10 photons/s

we still need to optimize phase, table position and improve the jitters...

317

Thu Jan 25 12:45:41 2024

mechanics | lasers and optics | cabling

controller M1 & M4 (plan mirrors) with IcePap controllers

this double motors scheme works good.

if motor P4 is used by increasing value, the FP-cavityPZT signal (pink signal on scope) goes HIGHER
if motor P1 is used by increasing value, the FP-cavityPZT signal (pink signal on scope) goes LOWER

!!! CAREFUL !!!
after each session, it is mandatory to put the motors back to their initial position to avoid FP-cavity misalignment.
on P1 : - 900 000 steps
on P4 : - 360 000 steps

Ronic Chiche wrote:

previously, we have connected motor M4 with an IcePap controller.
see this post : https://elog.lal.in2p3.fr/FPC/THOMX+commissioning/278

motor M1 (or P1Z) which was on the axis 9 on the ISP controller has been assigned to OC/OP/OCH.01-MOT.06

motor M4 (or P4Z) which was on the axis 12 on the ISP controller has been assigned to OC/OP/OCH.01-MOT.03

316

Thu Jan 25 10:15:28 2024

mechanics | lasers and optics | cabling

controller M1 & M4 (plan mirrors) with IcePap controllers

previously, we have connected motor M4 with an IcePap controller.
see this post : https://elog.lal.in2p3.fr/FPC/THOMX+commissioning/278

motor M1 (or P1Z) which was on the axis 9 on the ISP controller has been assigned to OC/OP/OCH.01-MOT.06

motor M4 (or P4Z) which was on the axis 12 on the ISP controller has been assigned to OC/OP/OCH.01-MOT.03

315

Fri Jan 19 18:05:42 2024

Adding one photodiode in reflection

this morning, I added a DET36 photodiode in reflection (I used a thin beam splitter) to better measure the coupling over the full beam size.
this DET36 photodiode is sent to the "laser locking" oscilloscope with the other signals :
CH1 :transmission
CH2 : reflection
CH3 : error signal or FP-cavity PZT (depending on the Laselock Monitor 1 signal configuration)
CH4 : laser PZT (Laselock Monitor 2 signal)

I kept the DET10 photodiode in reflection, but slightly misaligned to get the 500MHz laser harmonic without too much amplitude variation when locked (the lock behavior changes almost the center of the beam).
the DET10 photodiode is sent to the "RF locking" oscilloscope on CH1

314

Tue Jan 16 12:26:12 2024

lasers and optics | detectors and electronics

33MHz (FP-cavity vs RF) phase stability

this morning, with Vincent Chaumat, we made a beating (phase detection) between the laser 33MHz and the 33MHz coming from the Rigol generator locked by the 10MHz link onto the 500MHz ring generator.

once the laser and the FP-cavity are locked on the RF reference, the 33MHz phase detection is stabilized and confirm the laser/FP-cavity lock on the RF reference.

313

Tue Jan 16 12:19:35 2024

lasers and optics | detectors and electronics | software

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

Ronic Chiche wrote:

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...

Ronic Chiche wrote:

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.

Ronic Chiche wrote:

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.

312

Thu Jan 11 13:42:16 2024

lasers and optics | detectors and electronics | software

Ronic Chiche wrote:

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.

Ronic Chiche wrote:

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

311

Wed Jan 10 18:43:03 2024

lasers and optics | detectors and electronics | software

Variable focal lens validation

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.

Ronic Chiche wrote:

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

310

Wed Jan 10 15:21:46 2024

we plan to use Electrically Tunable Lenses EL-10-30-C NIR to build the ThomX telescope but they need to be compatible with the powerful laser beam.

for CW regime, on the datasheet (see attached file), the optical damage threshold is 10 kW/cm².
with 70W laser power and 1mm² beam surface (which is much smaller than the real beam size), we are at 7kW/cm².

for pulsed regime, with Daniele, we can imagine that the inner material is water (n ~ 1.3 in the datasheet).
One found a paper about laser induced electric breakdown in water (see attached paper) which give a breakdown field of about 1e8 V/m (see Fig. 1 of the paper) for 7ns pulse width.
with 70W average power, 33MHz repetition rate, 10ps pulse width 1mm² beam surface, one has an intensity of ~ 2e11 W/m² (or 2.7 GW/cm²)
I = E² / 377 => E = 8.7e6 V/m which is also much smaller than the breakdown value.

from the fig. 4 of the paper, it seems the breakdown threshold increases a lot for shorter pulses from 30 GW/cm² (~10ns pulses) to ~150 GW/cm² (~10ps pulses)
so, one can expect a good behavior in pulsed regime too.

can anyone check the validity of these rough calculations ???

309

Wed Jan 10 14:52:22 2024

lasers and optics | detectors and electronics | software

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

308

Fri Dec 22 16:13:27 2023

lasers and optics | detectors and electronics | software

Christmas shutdown

this afternoon, I checked visually what happens when the AC power of the UPS is broken down => the laser controller has still its "emission" button ON... no AC interruption.
so, I guess the UPS switched properly the output AC line from the input AC line to the internal batteries.

Ronic Chiche wrote:

this morning, I shut off all the equipements (especially the computer) except the ones powered by the UPS : laser controller, laser peltier controller, laser motors controller.
and I disconnected the cables from the power plugs of the wall (to prevent any possible overvoltage).

Jean-Noël Cayla will need to shut off the electrical shelf (the one powering the UPS) during the afternoon, I will check at this moment if the laser controller is still properly powered thanks to the UPS.

307

Fri Dec 22 09:46:18 2023

lasers and optics | detectors and electronics | software

Christmas shutdown

306

Mon Dec 11 17:21:32 2023

mechanics | lasers and optics | detectors and electronics

issue