this morning with Alice, we sent the Menhir 160MHz injected in a fiber (with 6mW at the end of a long fiber) into the laser amplifier, to look for leakage or damage in the first stages of the amplifier (the amplifier is totally off).

first of all, we checked for light scattering around the laser crate with a sensitive optical card => nothing

and then, we checked for light scattering inside the laser crate with an optical viewer => we just saw 1 or 2 small spots located at the end of an optical element at the 2nd stage level.
but it's difficult to understand the optical path and know the different elements with the 1st stage still in place.

we think it is mandatory to open the top of the crate and lift the 1st stage to have a better look inside the optical parts which are at the 2nd and 3rd stage levels:
we could remove the front side of the crate without any damage to any fibers in the crate.

we just saw 1 fiber, glued to an optical element on the 2nd stage, and going to the 3rd stage.
the 1st stage is just an electronics parts stage which seems easy to be removed.

... to be discussed...

this afternoon, we saw some electric cables badly connected to their power supply.
we fixed it by soldering them together and screwing the result to the power supply.
(see 1st image)

we lift the plate of the 1st stage and we check for optical leakage in the fibers (see 2nd image + picture of the top part of the cassette).
(Aurélien took several images)

without the 1st stage amplification, we saw some lealage only in the bottom part of the "optical cassette".
light was scattered mostly from one side (2 spots) and we saw also very weak scattering in the other directions.

with the 1st stage amplification, we clearly saw the losses from the bent fibers inside the top part of the cassette => it's a good sign.
but after the 5%-10% coupler (the one used for the diagnostic of the power to allow the use of the 2nd stage), we don't see any losses, which means there is no light in this part !
the fiber break could be in between...
Aurélien should send the images to Jérome to get a diagnostic.
the old schematic is attached but it has been modified in the Loic Thesis (p. 165)

we identified the black optics components as 2 isolators (AFW-PISO-30-1W-FB) and 1 circulator (AFW-CIR-PM-30) from AFW technologies.

this morning with Alice and Daniele, we removed all the optics elements and equipments from the SBOX optical table and started to clean it.
the dust meter count 0 on all particle sizes after the cleaning.

we observed a small part of the SBOX which seems to be oxydised (see picture).

the two previously used mirrors of the SBOX (C23018/7 and C23017/2) were already in their plastic boxes outside of the SBOX.
they are still on the optical table.

we have to decide which mirrors to put in the cavity:

if we don't want to use a "new" ThomX coupling mirror M1, we have to use a Gamma-factory mirror (161185) with T=460ppm for example (we don't have any other FS plan mirrors).

if we don't plan to work at high power in the SBOX for the moment, we could use an "old" ThomX M2 mirror with ROC=2.241m (C1611/11) to avoid any risk of contamination of a "new" ThomX M2 mirror.

this afternoon, we checked the dust meter which is at 0 for 1 and 5µm dust particles but ~ 2000-3000 for 0.3µm particles.

we opened the two top panels to let the air flow clean the inside of the vessel.

we observed some other minor oxydised regions (than the one taken in picture) on the external parts of the inox panels but at first sight, nothing inside the vessel.

friday morning, we add a zoom call with Jerome Lhermite about the amplifier repair.
he approximately confirmed the amplifier scheme from the Loic thesis.
he suggested to:

1) identify the circulator ports.
they have some tapes with text written on them.
the goal is to understand if it is still used in the present setup and if a CFBG could still be connected to it (and from which one end could be the fiber seen "broken").

2) use the 5% output tap of the amplifier to check if some light is outed if the input or circulator fibers are injected with 1st stage switched ON or OFF.

3) follow the "broken" fiber to check to which element it is connected to => we should need to unroll the fibers in the bottom "fiber cassette"... :-(

now, it seems the table is clean enough (dust meter counts 0 particles) to install a 2 mirrors FP-cavity.

today with Alice,

- we measured the height of the SBOX windows center : 140mm from the optical table.
- we set the laser fiber colimator exactly at this height.
- we placed 2 mirrors to align the future telescope path at exactly 140mm height along the whole possible travel of the lenses in order to keep them aligned.
the horizontal position is also aligned on this path and a ruler has been placed along this path to help to move the future telescope lenses without misalignment.
- we aligned 2 iris on this path to keep this path axis in case of misalignment.
- we placed 2 iris at the center of the input and output FP-cavity windows.
- we precisely aligned the laser beam on these iris.

in the next days, we need to align the mounts in the SBOX and align also the 2 FP-cavity mirrors.
the output mirror will be a "bad" ThomX 2.24m ROC ULE mirror and the input mirror will be a plan 460ppm Gamma Factory mirror.

With Alice, we installed the EOWaves oscillator to be locked on the FP-cavity (T1 ~ 2500ppm, T2 ~ 10ppm => F ~ 2500)
FSR = 216MHz => LW = 86kHz.

We installed the PDH box, and we got some error signal, but the shape of the transmission signal and error signal is a bit strange...
It grows smoothly, and when the power is large enough, one can see a sudden and fast drop.
Could it be some mechanical problem with the mirrors' mounts ?
I opened the SBOX this morning to do some inspection, and the mirrors seem properly installed in the mounts.

In some rare cases (last picture), the "instability" effect is not dominant, and we are able to maintain a quasi-lock during some 1- 2ms.
But it is still impossible to lock the cavity.

(We did a test with a vacuum in the SBOX at ~2mbar, but the problem is the same.)

After installing the 2nd EOM, we had some trouble to be able to lock again.
One possible reason was the very low signal level in transmission, which is important to trigger the locking system (and stop it).

See the Alice post for details, but we were able to measure only once the Finesse of the cavity at around 2600.

After the Finesse measurement, we opened the box to change the M1 mirror... so the box is at ambient pressure now.

I took back the avalanche photodiode from the Minicav room and installed it on the setup to replace the FPC transmission photodiode.
Now, the transmission peaks are at the 1V level, and it's very easy to trigger on...
The system locked very easily, even without being under vacuum.
It will help if we need to inject very low power laser (e.g. OEwaves after 2x EOM and AOM).

• Thursday 10 December 2020:   First Test Measurement - Inside Box
  •  The transmission ( T ) for the mirrors of SBOX and ThomX was measured over a range from the center of the mirror up to 5mm.
  •  
  • The first setup was initially done while the mirrorr is installed inside the metal box, when measuring T we observe that there is an erregular  change in the power measured as we move azay from the center of the mirror, this was due to reflection of light inside the box. The reflection from the mirror was reflected on the metal inside the box and it was measured by the power meter.

               (so for this setup we only took measrements for T along the center of the mirror)

The file stating the measurements is : Test Cavity _ Mirrors transmission _ Inside box

=======================================================================

• Tuesday 15 December 2020 :  Second Test - Outside Box
  • The setup for T test was moved outside the metal box with the same distances between the injection beam and mirror ~ 50 cm. and the distance between the injection laser and the mirror next to it ~ 9 cm.
  •  
  • Observation for T is done at full angle and at half angle of reflection ( the mirror was tilted to achive this )
  •  
  • we observed that after each change in the distance from the center the power meter needed to be aligned to have the max power.
  • after doing all the measurements for the range from the center we made it again for the center only and the consistance of the transmission was good.

The file stating the measurements is : Test Cavity _ Mirrors transmission _ outside box

note: the laser used for the test is the Koheras

details on the pwer used, mirrors, power meter, filters, ....etc are shown in the Excel data sheets

Done By : Loic , Manar and Ahmed

• We started measuring the phase noise on the OEwaves CW laser.
  • Class 3b
  • wavelength 1.5 um
• The procedure is done using self coupling of the laser
  • splitter 50%-50%\
  • delay line 100 m 
  • all fibers are PM type (polarity maintained)
  • Photodetector is "lab buddy", very fast diode.
  • Note: différance from schematic (we did not use a low pass filter)

a correction on the wavelength of the laser  it is 1030 um 

correction on unit 1030 nm

An Initial cleaning of the KBoX outside was done, All the optics and mechanics placed that were on the table were removed.

Only the old Mitylaser amplifier remains on the table.

Since we will be using the ThomX Celia amplifier, we will remove it and place it in a secure location (to be decided).

Tomorrow a cleaning of the inside of the cavity box is to be done.

The cleaning was done twice with half an hour interval between the two times
reading on the dust meter was taken after each time, and it was zero averaged over a 10-min

Migthylaser amplifier has been moved from the SBox table to the PLIC table.

In preparation for cleaning the mirrors.

The spincoater has been moved with its bump into the sas of the SBox.

The pure water used will be provided by Alice, as the previous source in the workshop is not available.

The inside of the cavity was cleaned today. It was very dirty and had big dust particles and fibers inside.

Cleaning was done for everything; wall, floor, fixed mounts, wires (still have some dust difficult to remove), edges.

The dust meter average was measured outside the cavity (2471 p/m3 av 6 min)  and inside after cleaning (1424 p/m3 av 10 min).

The cavity was left open under the clean air flow, will observe it under UV, clean and measure Dust tomorrow.

Images attached are after cleaning.

Objects inside the cavity at the moment :

• 4 main mirror mounts
• 4 mirror fixers on mounts and 3 screws each (total 12)
• 2 reflecting mirror mounts
• 2 dielectric mirrors (mounted and to be cleaned)
• two mounts for D-shaped mirrors.
• 2 D-shaped mirrors (unmounted, and they will need cleaning)
• 2 metal irises (pinholes)

After an overnight where the cavity box was left open, a measurement of the Dust meter was taken:

Outside on the optical table on direct air flux (1701 p/m3 Av 10 min) and

Inside the cavity box (998 p/m3 Av 10 min)

The dust inside the cavity has decreased by ~ 30 % for 0.3 u particles.

Note: the cavity box is still open.

The dust meter cap was cleaned using Alcohol, and using the filter white cap the dust count was (0 Av. 10 min)

After the dust counter was hand held in direct airflow, it counted (1581 p/m3 Av. 2 min).

I tested the count also in the SAS, and it counted twice the amount ~ 4500 p/m3

Note: discussion on the next steps to take for the airflow filtering !!!!!!!!