Center of M1:

First finesse measurement 20 266, FSR 133.351 MHz under vacuum

The kept transmission for M4 is 2.17 ppm. Which is the value measured after alignement (center of the mirror).

These measurements have been taken before alignement.

High dependence against the position. Few measurement several mm away from the center each one at different position give 194, 193, 208, 200 ppm.

At different positions, transmission give 194, 193, 208, 200 ppm?

The new mirrors didn't give expected results. Then the 4 old mirrors have been sent to LMA on 12/11/18 for a cleaning and caracterization before and after cleaning. Also asked for a diffusion/absorption map on the mirrors if possible. They didn't really answered on what will they do. 
Received on 13/11/18 by LMA.

Mirrors arrived today from LMA. Their features are damaged.

Photos avant ou après nettoyage, pas clair dans le mail de Laurent : 

"J'ai commencé à nettoyer M1 et M2 avec notr methode habituelle et je me suis aperçu que sur la partie centrale (en gros taille de ton faisceau j'ai l'impression) que des choses apparaissaient (voir photo)
Si bien que la diffusion n'a pas évolué dans le bon sens (diminution) voir empiré pour M1. J'ai donc arrêter de les nettoyer !!!
J'ai regardé les faces arrières des miroirs avant nettoyage et j'ai pu voir ce que tu vois sur la photo même au centre. Je sais pas de quoi cela peut venir.
Une chose est sûre le coating IBS a été altéré par je ne sais quoi dans ta manip provoquant cette dégradation dès qu'on y touche. L'interaction avec les faisceaux d'eélectrons n'avait jamais altéré les miroirs sur l'expértience DESY par exemple!!
Pour me rassurer, j'ai pris un miroir fait sur un micropoli qu'on a en stock et aucun pb lors du nettoyage (on peut penser à tout)"
 

Cleaning on dirty surface shows something is deposited on the surface. Cleaning displaces and removes part of the deposit.

All the mirrors show impacts on there surface (some of them do not show deposit). Does it come from experiments or fabrication ? Are these holes or bumps ?

Onefive output power is 24mW now, and 2.41mW(after EOM) injected into fiber,

a injection power monitor added, 99% (2.06mW)  injected into amplifier, 1% (16.1uW) monitored with photodiode DET36A/M, which gives ~500mV DC signal on oscilloscope with 1Mohm impedanc;

First stage amplifier works good, monitoring phtodiode gives more than 200mV DC signal with 50ohm impedance on oscilloscope (as attached photo);

Second stage, the old monitoring photodiode is broken, a new monitoring photodiode is connected, which we don't have reference data for it,

on the optical output port of the monitoring signal, it's written 150mW, but at where we measured 40mW.

I just had a phone call with Jérome and he told me 2 things :

* Be carefull ! the MightyLaser amplifier is not designed to work with 33MHz laser : the streching level is not sufficient !
One could worsen the phase noise by self-modulation due to peak power or even distroy the amplifier !
One should use it only at low power !!!

* He thinks we should more or less find back the same DC levels than before even with lower seeding power and lower repetition rate.
He thinks we should look at the optical spectrum to check if we don't have some ASE in the 1st stage and 2nd stage signal !
We can send him plots or call him to discuss these points.

XPS has been proceeded on the 400kW SBOX mirrors M3 and M4 (the initial cavity spherical mirrors) in frebruary 2019. Deposited a lot of particles on these mirrors.
All the mirrors received a Infrared spectroscopy the 12th of november 2019. Deposited glue on the non-reflective face (was used to hold them).
15th of november (2019): The four 400kW SBOX mirror's have been cleaned with aceton and isopropanol.
28th of november (2019): The four 400kW SBOX mirror's have been cleaned with spin coater.

Summary:

Aceton and isopropanol removed most of the particles and all the glue. But it let some traces on the mirror surface on all the mirrors (so there is some kind of grease on the surfaces).
Spin coater removes all the traces.

See pictures. On all the first images, we also see the dust which is on the non reflective face through the mirror. On M3 and M4 there is still the "glue" on the non reflective face on their frst images + refletive faces very dirty because of XPS.

The initial 400kW SBOX mirrors which have been cleaned ont 28th of november have been installed this morning on the SBOX.

Yesterday the cavity has been aligned and locked with the CW Koheras laser.

the FSR has been measured by modulation technique at 133.344MHz at 1mbar pressure in the cavity.

the polarization has to be optimized for the Finesse measurement otherwise, some "shoulders" appear beside the Airy peak and reduce Finesse fit.

once it is done, 3 consecutive measurements give an average Finesse of 20800.

the 2nd stage amplifier needed several hours (4-5h) to reach its nominal power (we look at photodiode level on a scope), instead of the awaited 30 minutes.

could it come from the probable spectrum shifting of the OneFive laser ?
(the power coming from the CVBG, coupled to the fiber, is lower than expected).

Last time, we switched ON directly the 2nd stage at 6A without increasing/decrinsing slowly the current.
today, we switched ON the chiller, switched ON the 1st stage, switch ON the power supply of the 2nd stage at 0A and then we increased slowly the current until 6A... and the problem disappeared.

2nd stage output power was going down. We checked the pump diode technical data sheet and the operating temperature is [25°C:35°C].
We increased the chiller temperature setpoint from 19°C to 23°C. 
Then the output power increased (93mW on 2nd stage photodiode).

Today, at 3A on the 3rd stage, we saw some HOM effects.
the transmissions is about 100mW which corresponds to 30kW inside cavity.
we tried to play with D shape motors but without success.

on the plot below, a mix between Thermal effects andHOM effects (the trans step at 13s is done without any external action)

-yellow : transmission
- orange : coupling
- blue : PZT correction

the camera video does not correspond exactly to the scope plot.
it is just an example of HOM effect.

Beam diameter behind M2 :

- 2nd stage @ 6A - 1kW inside cavity
sx = 2120 µm
sy = 2150 µm

- 3rd stage @ 3A - 30kW inside cavity

sx = 2260 µm
sy = 2475 µm