The SBox cavity setup was changed to have only 2 mirrors M1 plane and M2 spherical, both from ThomX

Distance between the mirror ~ 72 cm , increased from 70 cm to take into account the thickness of the ThomX mirrors

Two lenses (300 mm @ 50 cm , 200 @ 104 cm) were placed to have the beam radius ~ 0.55 mm.

The cavity was locked with a coupling of 60 %, for Finesse measurement the sweep was taken over 100 KHz of 2 seconds.

FSR ~ 210.00 MHz, line width ~ 8.56 KHz, Finesse ~ 24 500 .

The cavity was realigned using irises instead of pinholes, gave a better alignment.

The inside of the box, the spherical and the injection mirror were cleaned and placed back inside the box.

we see beating of fundamental mode, previously at the transmission point we placed a wedge to split the beam which resulted in an elliptical mode

we removed it and placed a very thin beam splitter, the beam is circular now.

The cavity was locked in air at a coupling of ~ 60-70 %

Finesse and line width measured five readings with a Finesse average 25095.08884  of a Gain ~ 8000

FWHM (KHz) = 8.2928
Finesse = 25323.0544

FWHM (KHz) = 7.9202
Finesse = 26514.4395

FWHM (KHz) = 8.5834
Finesse = 24465.8636

FWHM (KHz) = 8.4571
Finesse = 24831.2419

FWHM (KHz) = 8.6275
Finesse = 24340.8448

Theoretical and expected Finesse for the 2 mirror setup with the losses is calculated by Ronic for comparison between four and 2 mirror setup.

Update for Finesse measurement, The cavity was put under vacuum ~ 1.1*10^-1 mbar

and the alignment and coupling improved.

FSR = 210.1 MHz

Average Finesse = 25686.46222

 FWHM (KHz) = 8.2387
Finesse = 25501.5659

FWHM (KHz) = 8.2028
Finesse = 25613.2858

FWHM (KHz) = 8.0978
Finesse = 25945.3289

FWHM (KHz) = 8.1744
Finesse = 25702.3142

FWHM (KHz) = 8.1847
Finesse = 25669.8163

Concluded from Ronic's calculations, this could be the maximum finesse we might be able to obtain with this setup

with Gain ~ 8000

On Monday we adjust the frequency to match 2160.66 MHz and lock the Pulsed,

at the same time start we start with the CELIA amplifier.

The FSR of the 2 mirror (plan-spherical) Cavity was adjusted from 210 MHz to reach 216.643 MHz

it was done by having two reference irises, one at the injection point and one at the reflection 

then changing the position of injection plan mirror to slightly closer distance and monitoring the reflection on the oscilloscope to be max.

The cavity modes were still seen, and we had to only improve the injection alignment after.

Me and Ronic locked in air and measured the Finesse, which was bigger by ~ 20%

average Finesse = 30208.53614

FWHM (KHz) = 7.0179
Finesse = 30869.9522

FWHM (KHz) = 7.1257
Finesse = 30403.005

FWHM (KHz) = 7.1287
Finesse = 30390.4014

FWHM (KHz) = 7.2884
Finesse = 29724.5531

FWHM (KHz) = 7.3055
Finesse = 29654.769

Yesterday evening the cavity was Vacuum pumped up to pressure of 5.5*10^-2 and locked 

changed FSR to be 216.662 MHz and alignment a little and measured the Finesse

in Vacuum we have average Finesse = 30341.6265

FWHM (KHz) = 7.0592
Finesse = 30692.1961

FWHM (KHz) = 7.2186
Finesse = 30014.556

FWHM (KHz) = 7.1051
Finesse = 30493.7635

FWHM (KHz) = 7.1079
Finesse = 30481.9812

FWHM (KHz) = 7.1413
Finesse = 30339.2695

FWHM (KHz) = 7.1624
Finesse = 30249.776

FWHM (KHz) = 7.0239
Finesse = 30846.2719

FWHM (KHz) = 7.2614
Finesse = 29837.6477

FWHM (KHz) = 7.1935
Finesse = 30119.1768

a Finesse of 30k with the present mirrors :

T1=120 ppm ;A1=(2.6+1) ppm;
T2=1.5 ppm ;A2=(4.5+0.27) ppm;

corresponds to 39 ppm of additional losses for each mirror and a theoretical gain of about 11k.

To prepare for the amplifier. I installed the D-shapped mirrors after cleaning (using aceton and ethanol) between the cavity 2 mirrors.

Before closing, I observed the back reflection from M1 (injection mirror). both the injection and reflection lines were off, due to that there was an internal reflection hitting the walls of the cavity.

I tried to correct it by slightly adjusting on M1 without losing the mode, but unfortunately we lost it. 

Tried to go back to the original position using the reflection iris reference, with no success.

Cavity axis is lost, and we need to align again.

The D-shaped mirrors are installed properly and not cutting the path of the beam.

The cavity has been aligned again and 00 modes beating observed, and external reference points has been placed.

Adding information about the 2 mirror cavity setup (plan - spherical) that is currently installed.

From Aurélien at the start of the manipulation.

@ 0 is where the injection mirror is located

In preparation to measure the output beam profile from the amplifier at high power, I have placed two wedge mirrors just before the beam dump to be able to extract the beam.

One of the wedges was taken from ThomX bunker, also the HR and AR mirrors were taken to plic room in case we might need them

an updated setup is attached  

Beam divergence after amplifier 4.46 mrad

Before injecting into the amplifier, the pulse needs to be stretched using a CVBG, type attached.

the CVBG is to be used at a small angle, the beam shape and spectrum after the PBS is attached.

After measuring the beam profile, a mirror was placed to direct all the power for fiber injection

power before the fiber is 13 mW and the power injected is 6.19 mW

closing series

The current setup of the optical table attached.

The cavity is aligned and the lock of the fundamental mode has been attempted, but the mode is drifting too quickly to be able to follow.

I have placed the cavity under vacuum for a better stability.

a simple telescope for the CW was adjusted to having 2 lenses of 300 mm placed ~ 250 mm away from the colimator and 200 mm lens placed after it with 510 mm.

closing series

The amplifier was installed on the optical table next to SBox table.

The CVBG that will be used for stretching before amplification needs cleaning (they are very fragile, 'ask victor for best method')

The software to drive the diodes of the amplifier we have is not the compatible one.

Amplifier placed next to the pulsed laser on the table under the airflow

The output is in free space with height from the table of about 10 cm, note the injection height into the cavity is between 14 - 15 cm.

a power cable is placed but not plugged.

Connection to the computer is made using USB B on amplifier to USB A  (note need a longer cable, the available on is too short)

The cooling, to be connected to an outside chiller, will use the bottom one shown in the image attached.

The two water tubes, from chiller to amplifier,  has been marked. The size of the tubes from the amplifier fit inside the tubes from the chiller.

The software to control the CELIA amplifier is on the laptop that was placed in ThomX bunker.

I have placed it in the PLIC room next to the SBox table.

it is called 'Alphanov Control Software'

Closing series

The "ThomX" CELIA amplifier is installed on the optical table.
I added all the rubber pieces available between the 2 racks to isolate as best as possible the top rack, which embeds some fans, from the bottom rack from which the laser beam is going out to the FP cavity.

1ST STAGE
-----------------

if I put 1mW (minimum input power) on the input fiber of the amplifier and I switch ON the first stage, one can measure 7mW on the 5% output tap on the front panel.
then it is mandatory to check this power before swtiching ON the other stage.
this 5% output tap on the front panel MUST BE ABOVE 7mW

input power : 1mW => 5% output tap : 7mW => amplifier output : 260µW

with the present setup, I can reach 6.8mW of input power, but the 5% output tap seems to saturate at ~ 8mW.
in this condition, the amplifier output is around 800µW

the SMA connector on the rear panel does not output any signal with the 1st stage ON.

2ND STAGE
-----------------

then, one can switch ON the 2nd stage : amplifier output is around 1.4 W (without any iris or dichroïc mirror).

the SMA connector on the rear panel does not output any signal with the 2nd stage ON.

Beam size at the amplifier output:

to make this measurement, I switched ON only 1st and 2nd stage.

the dichroïc mirror seems to work the best in reflection at normal AOI !!!
it's strange as most dichroïc mirrors seem to be specified at AOI = 45° ! => to be checked ! => the dichroïc mirror was set on its wrong face !!! => problem solved

the 2 images correspond to the beam measured at 24cm from the amplifier output.
we cannot use the gaussian fit due to the pump beam shape which perturbate the measurement.
I used the FWHM measurement => DX = 2.6 mm, DY = 1.8mm

Pulse shape model:

dP(x,y,t) = DP * exp( - ln(2) * ( (x/DX_fwhm)² +  (y/DY_fwhm)² ) * sech²( t / tp )

=> can we use safely the Newport 20Z40DM.10 mirrors to transport the amplifier beam ?
they are specified for 500 W/cm² CW and 4 J/cm² for 10 nsec pulses @ 1064 nm.

• if I am correct, for the previous shape model, the average power is :

Pmoy (W) = 2pi / ln(2) * tp * DP * DX_fwhm * DY_fwhm * Frep

with DP=500W/cm2, DX_fwhm=2.6mm DY_fwhm=1.8mm, tp=77ps, Frep=216MHz => Pmoy = 3.5 W !!!
this means that we should not exceed this average power with these mirrors !?!

• if I am correct, for the previous shape model, the maximal energy density (in the pulse center) is :

DE (J/cm2) = tp * DP => Pmoy = 2pi / ln(2) * DE * DX_fwhm * DY_fwhm * Frep

with DE= 4J/cm2, DX_fwhm=2.6mm DY_fwhm=1.8mm, Frep=216MHz => Pmoy = 366 MW !!!
if one applies a safety factor due to the pulse duration ratio (77ps / 10ns) => Pmoy = 2.8 MW !
this specification seems much less restrictive !

=> can we use safely the Thorlabs BB1-E03 mirrors to transport the amplifier beam ?
they are specified for 10 kW/cm CW (linear power density) and  0.5 J/cm² for 10 nsec pulses @ 1064 nm.

• the linear power density (LPD) is defined as the average power divided by the beam diameter (1/e²)

LPD = Pmoy / DXY = Pmoy / (1.7 DXY_fwhm) => Pmoy = LPD * 1.7 DXY_fwhm

with LPD=10kW/cm and DY_fwhm=1.8mm => Pmoy = 3 kW

• for maximal energy density:

with DE= 0.5J/cm2, DX_fwhm=2.6mm DY_fwhm=1.8mm, Frep=216MHz => Pmoy = 45 MW !!!
if one applies a safety factor due to the pulse duration ratio (77ps / 10ns) => Pmoy = 350 kW !

this afternoon, with Fabian, we did some measurements on the 3rd stage.

finally we used the Dichroïc mirror at AOI=45°C as first mirror and a Thorlabs BB1-E03 as 2nd mirror to send the beam to the powermeter.
we put an iris to cut the pump beam part.

with only the 2nd stage ON, the dirchroïc mirror and the iris : P=0.4W

3RD STAGE
-----------------

IT IS MANDATORY TO SWITCH ON THE CHILLER

once the Alphanov software is launched, 4 windows appears on the screeen, one for each diode.
once the chiller temperature reach the set value (23°C in our case), one can start to increase the pump current.
(set "voltage adj." to AUTO)

the TEC of the first diode is not operative, then we decided to stop its current to 4A to avoid a too large temperature (in this condition, the temperature of the diode reach ~45°C !)
the other diodes temperatures are stabilized around 25°C

1A for all diodes       =>   1 W
2A for all diodes       =>   10.7 W
3A for all diodes       =>   22 W
4A for all diodes       =>   33 W
5A for diodes 2-3-4  =>   40.5 W
6A for diodes 2-3-4  =>   48.1 W

we stopped the measurement at 6A and we did not notice any change in the optical spectrum

During the optical spectrum measurement we tried to use a NDUV20 Thorlabs reflective filter to reflect the high power beam to the powermeter and let a few power part be transmitted to the spectral measurement.
unfortunatelly, the ND filter coating has been completly removed => DO NOT USE Thorlabs ND filters at high power !

this morning, I locked the FP cavity with the OEwaves CW laser and the "Fred fiber amplifier" used at 500mA of pump current.

the lock was much more easy than with the Koheras.

I had to change the 10GHz EOM which seems damaged as the modulation depth is very low and does not allow a Finesse measurement by modulation technique.
I changed it by a recently buyed 2GHz EOM... the modulation depth is large enough and we can make the Finesse measurement.

I took several sets of data and the average Finesse is 25.5k !

I locked the Koheras CW on the FP cavity but the lock was pretty noisy and very difficult to acquire.

I tried to produce some modulation sidebands close to 216MHz to measure the Finesse but the power loss was very small so, the signal to extract the Finesse would be unreadable !
(generator voltage was at maximum Vout = 0.5Vrms on 50 ohms... is it normal ? or the used 10GHz EOM suffers some problems ?)

At one moment, I lost the lock and was not able to find it again... it seems the Koheras is too noisy for this cavity (may be is it a good news for the Finesse ?).
Tomorrow, I will try to use the OEwave + amplifier to lock the cavity.

I recorded the pulse shape of the MENHIR 216MHz in its fiber injection setup.
the fiber is then connected to the Labbuddy photodiode (~ 15GHz BW) and then to the R&S RTO2000 4GHz scope (~ 100ps rise time).

1) I put a mirror just before the CVBG.
I'm able to get >8mW in the fiber.

as the pulses coming from the laser are not streched, they should be close to Menhir pulse width (~ 200fs).
then, what I measure here is only the pulse response of the measurement system.

2) I remove the mirror before the CVBG to stretch the pulse inside the CVBG
I'm able to get >6mW in the fiber.

the 1st plot is the comparison of the 2 measurements:
in blue, the pulse measurement w/o the CVBG
in red, the pulse measurement with the CVBG

the 2nd plot is the comparison of the pulse streched by the CVBG with the pulse w/o CVBG convoluted with a tp=77.4ps sech² pulse (sech²(t/tp)).
in red, the pulse measurement with the CVBG
in dashed black, the convolution.
(as the spectrum is changed by the CVBG, it is normal that both pulse shapes are not exactly the same).
tp=77.4ps corresponds to t_FWHM = 1.76*77.4ps = 136 ps

both pulses exhibit a FWHM duration of 194 ps.

with the present spectrum after CVBG (see 3rd plot), if the pulse was Fourier Transform limited (no stretched), the product of the FWHM (BW x duration) should be 0.315 (for sech² pulses).
FWHM BW wavelength ~ 1.1nm => FWHM BW ~ 311GHz => FWHM Tau ~ 0.315/311GHz ~ 1 ps
with 136 ps of FWHM duration, one can consider the CVBG has properly streched the pulse.

The chiller of CELIA amplifier has been moved from the corridor to the changing room in front of PLIC. 

It was not functionning well (quick drop of flow below 0.9l/min). After several cleanings of the filter, shorting the water circuit a stable 2.1l/min flow was obtained. Then the water circuit was elongated to go close to the amplifier but not into it. Allowing to get about 1.3l/min stable. Now the amplifier is conencted, the filter has been cleaned again twice and the flow seem stable with 1.4l/min. New filters have been ordered and must arrive quickly. Changing it is necessary I think. 

today, temperature of the chiller has been set to 23°C.

measured temperature in the chiller reaches 23°C after approximatively 10 minutes

Under the microscope,

the spherical mirrors show the deposit of metal dots on the reflecting surface and not on the back of the mirrors

The mirror with fewer spots near the center was used in the setup.

Mirror images in the previous log showing the metal deposit of the coating of the spherical mirrors

(not sent by mail due to large size of images)

The Sbox currently has the injection from ThomX installed T ~ 120 ppm , M2 planar from Sbox spare and M3 / M4 spherical mirrors from Sbox installed.

The last finesse measurement that was done gave a Finesse of ~ 19300 (After cleaning M2 using ethanol + aceton + pure water)

on Friday the whole optical table was cleaned again and the inside of the box was cleaned (even with a lot of dust inside the box the Finesse was 19300 )

all the mirrors were cleaned after using the three steps, M3 and M4 had clear visible dust on them.

D-shaped mirrors were installed again between M1 and M2

The alignment was redone and the beating observed ,  There is still a need for alignment improvement.

the cavity is under vacuum ~ 4.8*10^-2 mbar on Friday evening (~ 19h00) , The cavity is yet to be locked and to measure its Finesse

A PowerPoint showing the last finesse measurement and the error signal of the menhir laser lock

Max Finesse obtained @ 4 mirror setup was ~ 19 300 

With M1 from ThomX , M2/M3/M4 from SBox

Divergence of the CW beam out of the collimator measured after 1 meter to be 

• 2 x = 0.7425  mrad  --> x = 0.37125  mrad
• 2 y = 0.7115  mrad  --> y = 0.3575    mrad

two lenses were placed to decrease the diameter of the injected beam

Closing the series of the telescope for the beam @ 133.33 MHz

The current setup for the SBox has a beam viewer and 2 photodiodes placed at reflection and transmission.

The CW laser piezoelectric crystal was driven using the lase lock system to observe the 00 mode.

Mode Observed and has no reflection (from what was previously seen)

higher order modes are resonating with 00 mode , example 11 mode (shown in image attached)

the coupling is yet to be seen and measured.

Adding images from the transmission after the spherical mirrors M3 and M4 window for a resonating mode inside the cavity.

There appears to be some misalignment from the center of the mirror ???

Images of the Transmitted beam at M2 mirror at different days. 

The first one was from last week, the second from yesterday.

There is misalignment (drift due to temperature) from the position where the beam was initially. ( reference taken between centers of mode and direct injected beam) 

it is most clear in the vertical position.

Closing series of 00 mode for FSR @ 133.33 MHz

Start with the cavity lock images attached, taken from last week, at start we have a coupling ~ 5%  and started improving on the alignment .

The image of 00 modes attached corresponds to the coupling seen on the oscilloscope.

We have a higher coupling with the 11 mode due to the size of the injected beam in comparison to mode

lenses were added to improve it.

Current setup at SBox for locking the cavity

After spacial matching, the coupling increased to ~ 15 - 20 % 

The locking was done for the fundamental mode, tried to improve the coupling with the motors, but the lock is very unstable to be investigated. (Note: the cavity in under normal pressure)

Cavity locked today under vacuum and no airflow, it is stable over a long time

the alignment was improved and an increase of the transmission by 20 % from its original value

unfortunately,  data from the oscilloscope was saved, but it was not in the correct format (image) to show.

Attached ; the mode shape, the new motor positions. 

Closing the series for the setup

The cavity was only locked @ 133.33 MHz but the Finesse was not measured

The FSR was changed to match the new laser MENHIR 216.6625 MHz 

The SBox Length (FSR), was changed to match the repetition rate of the Menhir pulsed laser Frep = 216.6625 MHz

It was changed by removing the 2 D-shaped mirrors placed between M1 and M2, distance between M1-M2 ~= 169 mm 

it was still needed to be adjusted with M1 motor to reach the correct FSR.

The pulsed laser is placed on the able with injection into a fiber

The Finesse of the cavity has progressed from ~2500  to ~ 18 000

** Note: PowerPoint attached shows the progress over the last two weeks on the laser and 

Starting with the alignment of the KBox using CW Koheras.

The size of the CW output from the collimator at 1 meter from is ~ 2.4 mm, to be adjusted with lenses to match the cavity !!! (attached image)

For the 2 alignment mirrors, I am only able to control 3 axes for now (motor issue for the fourth to be fixed !!) , Horizontal and vertical for Ma1 and Horizontal for Ma2(closes to injection window).

Started with only irises placed on both the M1 and M2. Placed a beam profiler at the window behind M2 to observe an output beam.

Motors position for the 3 axes and beam shape and position after M2 attached.

SBox alignment, using CW laser Koheras power 1 mW

• Finished M1 and M2 alignment using the diffraction patterns seen on the beam profiler,  the beam fit is not very good ?? (image taken)
• Positions of Ma1 and Ma2 motors are registered (image taken)
• Placed Fixed 2 irises at M1 window and M2 window (Image taken while both are closed)
• Distance between the collimator and beam profiler ~ 2 m
• Distance between collimator and M1 diaphragm   ~ 1 m
• Distance between collimator and M2 diaphragm ~ 1.6 m 

After pointers and Advice from Aurélien,

improvement of the beam alignment through M1 and M2 irises was done.

To improve the image on the beam profiler, I cleaned the alignment mirrors and the windows using pure ethanol and optical lens cleaning tissue,

a significant improvement after cleaning the inside of M2 Window. Images have less dust diffraction rings.

Attached new images of the beam:

• New Ma1 and Ma2 motor position
• After M1 pinhole optimized (saturated)
• After M2 and M1 pinhole optimizing (saturated and not)

Remember to update the position of the reference Irises tomorrow !!!!

• Adjust the placement of the Irises  (done at the start of the day, adjusted at the end when M1 mirror was placed)
• Improvement on the Ma1 and Ma2 (The Alignment Mirrors)
  • Improves the alignment a bit. There is an observation where there is no symmetry in the image, concluded to be because of the pinholes that are usually used for the alignment the circle cut is not symmetric (took images on phone of pinholes)
  • This explains why, for the pinhole used on M1, we see a little more symmetry than the pinhole used on M2. 
  •  
  • Placed M1 mirror from Sbox (with damage spot in the middle), after cleaning it using the spincoater, only used to adjust the injection into the mirror where it will give Horizontal displacement due to the thickness of the mirror.
  • Last position of the motors attached
• Installed the 2 dielectric mirrors for the reflection line
• Did a rough alignment for the reflection line to have it exit through the reflection window.

Note about mirrors : They were cleaned a year a go and placed in the boxes. When opened the box and seen under microscope they were very dirty with dust particle 

Specially from the back, I believe the boxes have dust in them (to be verified under the UV light /  Microscope  !!!!!!!! )

Finished the alignment of the SBox with M1 of SBox placed, to be changed to gamma factory mirror later

Observed what seems to be transmission through M2 mirror, to be confirmed. image attached shows it

a PowerPoint attached showing the details of today's work.

Last week In FP cavity we had all SBox mirrors including the damaged M1 mirror.

The beating was observed with just a slight adjustment on M4 alignment.

In addition, it was also observed while driving the piezo of the CW laser.

In the attached image of the beam at transmission point at M2 mirror, the shape of the beam is deformed.

one of the factors could be related to the damaged spot on M1 mirror. The deformation position can also be seen in the higher order modes.

after changing the injection mirror to Gamma factory M1, this deformation should disappear.

Today; replaced the M1 SBox mirror with M1 from gamma factory , following the previous alignment.

Removed all mirrors and cleaned them one by one.

Started with no M1, placed M2 did its alignment through M3 pinhole, then placed M3 aligned it through M4 pinhole, then placed M4 aligned it through M1 pinhole.

Placed M1 Gamma factory at the end

Note: mirror is new was not used before, took image on microscope there was no dust in the center, but there was little on the edges (cleaned it using spin-coater)

beating of fundamental mode observed (at M2 transmission) immediately with very higher order modes, slight adjustment on M4 suppressed them.

The beam is not circular and still has some deformation, M1 was changed, so it could be a damaged point at one of the other mirrors (to be investigated tomorrow)!!

No significant damage seen on the other mirrors.

Yesterday, to find the source of why the mode is deformed, I tried to rotate the mirrors to see if there is a change.

I started with M2 and rotated it by ~ 90 degrees, there is a change in the shape of the beam.(image attached)

Will see if changing M2 to the spare M2 from SBox can fix the issue.

At the end of the day, alignment was lost.

will be redone today while changing M2 mirror.

M2 Sbox changed to spare. Alignment of M2 was redone. 

With the help of Ronic , We observe fundamental mode of the cavity with higher order modes. A frequency scan on the piezo was done to find the beating frequency , the shape is elliptical with no clear deformation.

The beam seems to be hitting something, which causes a reflection seen on the beam profiler.

We started a slow scan to improvement of the outside alignment.

At the end of the day, I can only get the TM01 and TM10 modes,

alignment to be continued tomorrow + the scan offset

Note: observation on TM01 and TM10 modes, we clearly see that the beam position is different from the mode center position !!

The external and internal alignment was redone.

External Alignment : the collimator position moved so in order to have a good start I placed 2 metallic mirrors and did a rough retrace of it's line through the cavity box.

It helped as I did not have to do a lot of adjustment on Ma1 and Ma2 position (new position attached)

Internal Alignment: I replaced the 2 pinholes inside the cavity box with another set where the holes are more symmetric, it shows in the alignment.

Images attached of the beam diffraction pattern after each mirror pinhole.

The injection mirror was placed at the end of the alignment.

Alignment Done !!!!!!!!!!!!!

Closing Series for Alignment.

Beating observed, beam is in the locking stages

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.

Used the spincoater and pure water to clean dielectric mirrors which will be installed inside the SBox for directing the reflection line.

The method : place pure alchole on mirror - wipe it using white sterile tissue (in one direction) - clean with pure water in spincoater suing cotton swap .

After multible rounds, the result in the images was obtained. there is still a significant amount of dust particles (not all could be dust!!).

Not sure if the reason is the cleaning method ?? will invistegate it more !!!

Images of the SBox mirrors cleaned at the same time when the cavity was aligned.

Directly from the spincoater to the SBox directly.

PowerPoint attached shows details

PowerPoint shows the detailed images of all the mirrors before and after cleaning.

Images of SBox mirrors and M1 from Gamma factory attached only for the front after cleaning

the lines showing are on the back of the mirrors, they come from the spinning mount the mirrors are fixed on in the spin-coater.

Naming code :

               M#BB - M# mirror Back Before cleaning

               M#BA - M# mirror Back After cleaning

               M#FB - M# mirror Front Before cleaning

               M#FA - M# mirror Front After cleaning

               G : Gamma factory

Following the observation that when rotating M2 plan mirror of SBox the deformation position of the mode changes.

M2 was replaced with M2 spare of SBox

images of the mirror front side attached before and after cleaning, no spots at the center, but there seems to be 2 spots far from the center of the mirror.

After comparing with old images of M2 SBox spare, they do not appear to be damages, but dust !! (old image attached, taken on 10/12/2020, was never opened after)

While repeating the alignment, the mirrors were cleaned using the spin-coater and placed again.

The current mirrors placed in the SBox are

M1 plane injection from Gamma factory

M2 plane from SBox spare

M3/M4 spherical from SBox main set

no visible damage seen on the mirrors with the microscope

no images of the surfaces were taken due to time constraint.

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 !!!!!!!!

Dust measurement done today on  top of the SBox average 10min

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

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.