Measurement on 24/10/18

Measurement on 25/10/2018

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 ?

29/02/19 - AFM has shown that spots on mirror's surfaces are bumps and not holes.

30/01/19 - The following powerpoint shows the results discussed with LMA people.

What came out from the discussion is:

- Their cleaning method uses demineralized water drop on a spinner. It is probably the explanation of the circular traces on the mirror's surfaces but we still don't know what is this deposit (XPS is running out on 2 of this mirrors at this time).

-  According to their point of view, the spots could come from the coating deposition technique and are "normal". No real explaination, should not come from the substrat which is ultra-polished but can come from some clustering in the coating.

We gave them 2 of the mirrors so they can check if it is possible to clean them. They'll also do a measurement of the mirror's topology.

AFM+ InfraRed spectroscopy (IR spectro) has been performed on 400kW S-BOX mirrors.

Seems that XPS made M3 and M4 dirty, but M1 have also ome dust. M2 seems clean, further AFM experiment should show that it is as clean as M1.

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.

The mirrors went in the cavity the 28th of november (We did several power up to 30kW stored and only one to 40kW then the power went down to 2kW during the run).

Microscope study shows that mirrors get some dust during the handling [travel from microscope to SBOX --> installation --> in SBOX for +1month and power up --> travel to microscope].

Almost all of these dusts can be removed with cleaning.

There is only one important difference between 28th of november and today, a large spot on M1. 

AFM has been proceeded on M1 and M2.

The pdf shows the first images taken with the PLIC room Leica microscope (zoom x10 and x80).

Then the hole has been studied with a handmade microscope. It brought a better resolution. We can now see the hole has an edge, a center structure and and extra-hole sparkle (pailleté) structure.

The AFM shows these 3 structures are real. The top of the hole is at ~+1µm and the center ~-2µm compare to the coating surface. The sparkles are ~10nm high and we also found kind of "explosion" desposit while zooming on the sparkles.

The 3D view and profil show perfectly the "crater".

We had enough time to proceed a quick scan of M2 which has also a hole but not centered on the mirror.

The hole is larger and higher than the one on M1. But the vertical range was to high for the AFM. Then we cannot see if there are sparkles or not on this image. Further study with microscope would be welcome.