today, we were able to store more than 97kW in the FP cavity, always with the same parameter : 33% laser amplifier ratio

yesterday, we were able to store more than 98kW in the FP cavity, always with the same parameter : 33% laser amplifier ratio

the previous password has expired.

the new access from the computer :
login : .\$jehanno
pwd : ThomX23456

the new access in remote:
login : $jehanno
pwd : ThomX23456

last week, we measured the transmission of a plan mirror from the same batch than the ThomX mirrors and we got ~ 1.75ppm instead of 3ppm which was the calculated value by the LMA.

previously, we put 1/3ppm = 333 333 as multiplication factor.
from today, we will put 1/1.75ppm ~ 570 000 as multiplication factor.

then, previously we got 50kW, now we should get 85.5kW instead in the same conditions.

the 2 files describe the specfications for the16  mirrors ordered (4 for ThomX + spare, 4 for SBOX + spare) and the measurements made by the LMA.

Before, the locking scheme was to produce an error signal with the PDH box, send its output to the electronic amplifier box and then to the laser EOM for the fast loop and to the Laselock input. The drawback was changing one loop gain, changes also the other loop gain.

Now, the locking scheme is the error signal coming from the PDH box is directly sent to the Laselock input and in a same time to the electronic amplifier box which is only connected to the laser EOM for the fast loop. then, one has the fast loop gain which can be changed with the electronic amplifier box, one has the slow loop gain which can be changed on the Laselock and if one needs to change global gain of both loops, one can move the PDH diffuser.

This scheme is currently used and locked the setup.

from now on, one reverts the FP cavity motors direction to compensate the long drift from the begining of the project.
the motor MOT.06 will be used for the upward direction (presently -1 082 650 steps)
and the motor MOT.03 will be used for the downward direction (presently +37 170 steps)

after CEP and walking alignment tuning, I got quickly 92kW.

the new MOT.06 and MOT.03 positions are : -1 071670 steps and +34 110 steps.
the CEP motor is at +345µm

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.

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 we tested a mirror from one patch

image is for the front face of the mirror

PowerPoint has more details about the images

Motors are connected. The true mirror's name are P1 for injection mirrors, S2, S3 and P4. (S=spherical, P=planar).

They are still some old schemes (and notations on the cavity) which mention M1, M2, M3 and M4. I make the link here:

M3 = P1
M1 = S2
M2 = S3
M4 = P4

The wires are plugged as follows (I use notations wrote on the cavity and wires):

M3x = 1-1
M3y = 1-2
M3z = 2-1

M1x = 1-3
M1y = 1-4
M1z = 2-2

M2x = 1-5
M2y = 1-6
M2z = 2-3

M4x = 1-7
M4y = 1-8
M4z = 2-4

S2 and S3 z-axis are initially at 1/4 (5mm/20mm) of there range over ~20mm range. This is meant to be able to spread them up to ~15mm in case of thermal effect.

Actually, they are in an opposite position. Means that they can only be spread of 5mm from the initial position.

All Z motors (for P1, S2, S3 and P4) have been initialized again with a proper HOME command with their own controller  with the "superviser" software (which means they all moved to the +1650000 position).
Thus, they have been moved to their default position : +825000 for spherical mirrors (S2 and S3) and -825000 for plan mirrors (P1 and P4).

reminder : lower values on the motors makes the motor tip going inside which makes the cavity length larger.
thus spherical mirrors are in default position with a possible big range to put inside the motor tip (for thermal effects compensation).
by complementarity, plan mirrors are in default position with a possible big range to put outside the motor tip.

the Labwindows CVI was buggy about the proper representation of the motors motion in Z direction (wrong direction and wrong default position).
the software is now fixed.
 

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.

30/01/19 - As LMA people came, we discussed about the spots on ThomX mirrors which should be clean. As mentionned in "SBOX commissioning", these spots are normal.

An other question appeared during the conversation about the storage time and location of these mirrors. They have been stored for more than two years in plastic boxes. LMA people explained that some company do not let anything more than 6 months in these boxes for pollution issues.

We merged into the same conclusion, clean the mirrors in case of pollution. Finally, they took the mirrors and we will go to LMA to recover them between 11/02 and 14/02. 

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 ).

29/01/19 - ThomX mirrors have also been checked with binocular microscope. They shown the same spots as S-BOX mirrors. 

1st image shows reflective face of a spherical mirror.

2nd image shows reflective face of M1 (sapphire).

Summary of what have been cleaned the last week:

P1 with isopropanol, finesse 11000
P4 with isopropanol, finesse 13000
S2 with isopropanol, finesse 13000
S3 with isopropanol, finesse 14000
S2 with isopropanol, finesse 14000
P4 with isopropanol, finesse 12500
P4 with isopropanol, finesse 12500

Finesse decreased with last steps which probably means our cleaning technique is at its maximum. We will probably try a cavity axis change with the mirror's motors to increase the finesse  to the maximum like that.
Next step is to clean P1 with acetone + pur ethanol, then install the Onefive.