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.

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. 

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

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.

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 ).

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.

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"

After mirrors were going back from LMA for cleaning and thermal anealing, they have been installed in FP cavity for Finesse measurement.

after getting strange results when the cavity is closed (very low Finesse...maybe too much ethanol inside cavity procucing some lineic losses), we get 12k-12k5 Finesse with primary vacuum (~4 mbar) and a clean lock (very flat transmission signal and quite noiseless reflection signal)
we let the cavity pumped all the WE to see if we can measure a difference or not at lower pressure.

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.

To complete these observations:

Finesse has been measured on thursday, right after cleaning the cavity with ethanol @6000.
Finesse has been measured on friday, after opening the cavity for few tens of minutes @12000-12500. The cavity was openned while locking and the transmission was continuously and ~linearly increasing.
Finesse has been measured today after ~50h pumping with primary vacuum @17000. It's back to the highest value we've ever measured on this cavity.

Parameters @17000 finesse:

Input power: 7.85 mW (Koheras + AOM + 2*EOM)
Coupling: 70-75% => Pin ~ 5.9 mW
Transmission through S2 and P4: 50 µW (transmission estimated to 1.5 ppm) => Pcav ~ 33 W => G ~ 5600
It is compatible with a simulation with nominal parameters for mirrors and adding 47ppm by mirror of losses (absorption and scattering) which indicates 17k of Finesse and 4100 of power gain.
in this simulation, the coupling should be 94% instead of the 70-75% measured. It is possible that the losses (47 ppm) are not the same on all mirrors.

The ThomX M2 has been measured between 1.5-1.6 for x and y

We've added a clamp in the 3rd stage to prevent the pump fiber from moving and tilting (it was tilting to the left).

FSR is 33.347 MHz @1e-8 mbar

Fiber injection is finished with the new ThomX stretching CVBG in double pass (+50% injection power compared to K-BOX CVBG in simple pass).

- Output Onefive: 27 mW
- After Onefive + lambda/2 + isolator: 25.8 mW
- After Onefive + lambda/2 + isolator + lambda/2 + PBS + CVBG*2 + PBS: 9.6 mW
- After injection into fiber and EOM (+all preceding): 3.2 mW
- Input 99% of the amplifier: 2.86 mW

> 660 mW on 1% photodiode DET100 @1Mohm

The Onefive spectrum has shifted a little bit to lower lambda. It's still enough for the experiment (3mW injection of ampli intead of 1mW needed).

Yesterday, we've observed the first degeneracy on ThomX cavity at ~115 kW stored. The shape of the stored power on the oscilloscope is really close to what has been published in the D-shape mirror's paper ("tek0000" transmission in yellow, piezoelectric activator in green, error signal in blue).
This mode could be a 8.0 or 9.0. 
We have also observed a change of the angle of the mode (the pictures "degenere", "degenere2" and "degenere3" were taken by order). The only changing parameters are the alignement and the length of the cavity. 
The last thing we noticed is the shape of the mode which could not be an hermite-gauss mode (Bessel mode ?).

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.

The ouput power of the ThomX amplifier has been measured as a function of the 3rd stage pumps current (0A is 1st and 2nd stage turned on).

We measured the total power, the total power without the "donuts" pump signal dumped by an iris and the transmission of a dichroic mirror (for ref see image).