Observation made with IR Beam Viewer: 

The observation of P1 and S3 simultaneously while locking shows much higher diffusion on the ULE mirror. The diffusion on the two other ULE mirrors (S2 and P4) shows similar diffusion as S3.

14/05/19:

New Suprasil mirror received. It will replace the S-BOX suprasil mirror on ThomX which was already replacing the sapphire mirror.

First finesse measurement: 14000

Features sent by Christophe Michel:

"- Transmission mesurée (1064 nm)= 172 ppm ; Transmission estimée (1031 nm)= 140 ppm
- Réflexion (1064 nm)= 1025 ppm; doit être inférieure à 1031 nm
L'AR n'est pas bon alors que l'on obtenu 170 ppm pour le run de calage!
J'espère que vous pourrez néanmoins l'utiliser.
- Diffusion moyenne sur diamètre 12 mm: 2.6 ppm"

19/09/2019 : email from Chrisophe Michel about AR coating of LMA mirrors after reading that Ta2O5 layers can be damaged in vacuum if not protected by a SiO2 layer :

"oui tous nos coating standards HR se terminent par une couche de protection SiO2 Lambda/2.
Dans certains cas (spécifications du projet) l'épaisseur de la couche de silice de sortie peut être ajustée. 
Par exemple pour matcher une transmission très précise.
Pour les coating AR la couche de sortie est en silice mais pas lambda/2.

20/09/2019 : new email from Chrisophe Michel after he sent back the mirrors (LMA made a cleaning and thermal annealing) :

"le colis avec les 4 optiques, nettoyées 2 faces après traitement thermique et caractérisation, a été envoyé cet après midi par DHL (tracking number 4995967550).

Dans le colis j'ai ajouté le miroir en saphir C16115-11.

Les mesures donnent des absorptions entre 0.12 et 0.5 ppm (nous avons réussit à faire fonctionner de nouveau le banc mais il est mode dégradé avec une incertitude plus grande sur les mesures mais l'ordre de grandeur est bon et correspond aux valeurs mesurées en 2016 qui était de 0.24 ppm).

Pour les pertes par diffusion voila ce que Laurent à mesurer (les valeurs sont identiques à celles mesurées en 2016 sauf pour le C16116/11):

- C16116/11: 9 ppm sur diamètre 10mm (6 ppm mesurées en 2016); 4.5 ppm sur diamètre 6 mm; T=1.5 ppm @ 1064 & 1031 nm (simulée)

- C16116/12: 8.5 ppm sur diamètre 10mm; 4.5 ppm sur diamètre 6 mm; T=1.5 ppm @ 1064 & 1031 nm (simulée)

- C16116/13: 14 ppm sur diamètre 10mm; 10 ppm sur diamètre 6 mm; T=1.5 ppm @ 1064 & 1031 nm (simulée)

- C16115/11 (saphir): 9 ppm sur diamètre 10mm; 4 ppm sur diamètre 6 mm; T=148 ppm @ 1064 nm soit 120 ppm simulée @ 1031 nm"

Today, Axis 9 (Z-axis of P1) has blocked the software which drives all the motors.
impossible to bypass the problem.

I had to :

- switch off the motor driver crate n°2 (motors 9-16)

- disconnect all motor cables (9-16)

- reconnect only cables 15 and 16.(same internal board of crate n°2)

- restart the software to test that, now, the software launches properly

and I did again the procedure with connecting all motor cables

Today again, same problem with axis 9 blocking the controlling software during the mirror alignment procedure.

after opening the motor 9-16 controlling crate, we saw 2 screws (RX- and TX+ of the controller) which were badly screwed.

we firmly screwed them... could it be the cause ?

after reconnecting everything, the software launches properly... and everything is back to work... wait and see.

Several experiments have been done in order to check the potential source of dust in the ThomX cavity. For each step, we look at a clean surface, put the cavity under vacuum, go back at ambient pressure and check back the "clean surface".

1st: Primary pump on
2nd: Primary pump + Turbo pump on
3rd: Primary pump + Turbo pump + Ion pump on
4th: Primary pump + Turbo pump + Ion pump on + 10 "open/close" displacement of the pneumatic valve
5th: Primary pump + Turbo pump + Ion pump on + 1 full range displacement of P1 z motor
6th : Primary pump + Turbo pump + Ion pump on + RGA

None of these experiences have shown good correlation with dust generation. 
The RGA has shown reasonable values.
Conclusion is that dust was already in the cavity and was only displaced by all combined motors, pneumatic valves, cavity opening and closing movements.

Christophe MICHEL told us more precise informations about spin coater cleaning.

They always clean with pur water and cotton tipped sticks.
First a spray of water, then they put the wet cotton tipped sitck onto the mirror from the center to the edge ~x3 while continuing to spread water. They finish by putting more water without the cotton tipped stick.

WARNING: WATER HAS TO BE CHANGED EVERY DAY 

They said they only use clean water but in case of grease/oil onto the mirror they would use first acetone then clean water.

The cavity has been cleaned then put under primary vacuum (primary pump without vacuum flow control). Dusts presence was checked at air and no significant changes have been observed.

1ST image before cleaning
2ND image after cleaning
No changes after coming back from primary vacuum

Mirrors have been sent today to LMA for cleaning and maybe annealing (recuit). 3 ULE of ThomX and the fused silicate for injection (trans @140ppm ).

Last Finesse measurement in air : ~ 17 000 the 20th of may (see logbook)

28th and 29th of august, we cleanned, with Loïc, mirrors S3 then P1 successively using only ultra pure water with the spin coater.

we measured the finesse after each cleaning by modulation technique and in both cases, F ~ 12 500 !!!

maybe the mirror surfaces have been covered by some hydrocarbure during the summer ?
or by an other contaminant which is difficult to clean with only water ?
we decided to clean the mirrors first with an isopropanol solution and then with ultra pure water and the spin coater.

today I cleaned S3 with isopropanol and then with pure water on spin coater.
Finesse is only 10 700.(coupling 50% ? => to be confirmed...)

maybe we have to redo the procedure with a different way of cleanig (pushing less on the mirror ... ?)

Following finesse measurements (start @10700): 
Clean P1 with SC (water) + isoprop (wipe) finesse @15000
Clean S2 with SC (water) + isoprop (wipe) finesse @13000
Clean P4 with SC (water) + isoprop (wipe) finesse @11000

We have to take into account that "cleaning" the mirror change the alignment axis in the cavity so the finesse can change because of that. It would explain the erratic nature of these results which seem to not show any effective cleaning.

looking in the vessel of the FP cavity using a UV lamp shows a lot of dust... more dust than outside the cavity !!!

here is picture where one can see a cleaned zone using a finger (with gloves).

question : where does come from this dust ?

2 possibilities :

- large and small belows which could trap the dust and release it during the pumping process

- ionic pumps could release some clusters when they are working.

we plan to clean as effectively as possible the inner surfaces, to close bellows, make woking ion pumps to check if it released again some dust.

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.

Onefive output power : 28mW
Power before fiber injection : 7.8mW
After EOM and 99% coupling fiber : 1.8mW
After EOM and 1% coupling fiber : 14 uW (~1%), ~7.5V @ 1MOhm on DET36
Frep : 33.326 MHz
Output 1^st stage + collimator & dichroic mirror: 36uW
Output 2^nd stage @6A (~260mV @50Ohm on DET36): 300mW --> after 20-30min

Output 2nd stage is the same value as Onefive 133.33MHz

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. 

A new design has been studied for the 5 PDH boxes to better match the low (33MHz) repetition rate of the ThomX laser.
the 5 PDH boxes have been modified and tested (see the attached report).
A mixer has been integrated to the PDH box for a more simple use.

the PDH N°1 has been lend to Huan for her experiment in China.

telescope of Koheras is removed, information record here:

- distance between collimator edge and -50 lens mount edge is 14.7cm,

- distance between another edge of -50 lens mount and +250 lens mount edge is 14.3cm,

- distance between another edge of +250 lens mount and edge of bread board is 25cm.

Polariztion measured with Input vertically/horizontally polarized (~100% DOLP)

- Transmission (P4) locked on cavity horizontal polarization is ~50% linearly polarized and ~50% unpolarized ?

- Transmission (P4) locked on cavity vertical polarization is ~50% linearly polarized and ~50% unpolarized ?

Voyage Bordeaux au CELIA avec Jérôme LHERMITE (Loïc et Titoutan)

1^er jour (34°) :

Mesure du spectre et de la puissance des 4 diodes de pompe 3^ème étage jusqu’à ~60W (12A).
Mécanique et câblage ampli.

2^ème jour (30°) :

Soudure des fibres des diodes de pompe 3^ème étage avec les fibres du recirculateur.
Câblage entre les 2 boitiers et fixation des fibres dans le boitier du 3^ème étage.

3^ème jour (26°) :

Connexion refroidissement à eau du recirculateur (chiller).
Soudure fibre CFBG avant 1^er étage (temporaire pour faire des mesure).
Mise en place des éléments 1^er et 2^ème étage sur le support de l’ampli.
Montée en puissance 35W.

4^ème jour :

Adaptation du mode de sortie en contrôlant la position de la fibre avant le collimateur.
Mesure de M².
 

M² mesuré à 10W.
M²x = 1.17
M²y = 1.14

See image.

5 Files attached:

- Note on the technique and results for the present cavity on 2019, May 21th : F ~ 18 000

- 2Tektronix scope raw data

- 2 matlab files to fit the scope raw data and extract the Finesse

15/05/19-20/05/19:

Cleaning of the mirrors:

Initial finesse 14000 @air
S2 with isopropanol, finesse 17000 @air
P4 with isopropanol, finesse 17000 @air
S3 with isopropanol, finesse 17000 @air
S3 with first contact, finesse 17000 @air
S2 with first contact, finesse 17000 @air

Power of the 33MHz Onfive decreases over time. Have to pay attention to that.
Note that air dryers have never been stopped.

10th april 2018: ~40mW (first picture, 10dB filter)
25th september 2018: ~36mW (second picture, 10dB filter)
16th april 2019: ~29mW (third picture, no filter)