I tested the status of several EOMs by injecting them with the CW OEWaves laser. Its power is of 15.37mW. 

With the viewer one can see where losses are located. For 3 of them, there is no power at output (nW).

for S/N 11419-12 and 10305-09 some losses are visible at the splicing point (IN side) of the EOM metallic case. 

for S/N 12487-02 some losses are visible at the input connector of the fibre. Maybe soldering a new connector may fix the issue. To be tested.

for S/N 2559-22, 6mW are observed at output. Slightly more losses than the design but may not prevent regular operation with it.

Yesterday evening, we closed Cavity Box and placed it under the primary pump for ~2 hours. then for lack of time we switched it off (did not want to leave it overnight as it could heat up).

After closing the valve connecting the pump with the cavity and switching the pump off, a slight increase in pressure happened and then a very small increase over time (can be seen in plot attached )

today we turned it on again until we reached a stable value , took ~ 3 hours

min value reached with pump on = 6.4*10^-2 mbar

value after switching pump off = 6.5*10^-2 mbar

at the end of the day ~ 7 hours after stopping, the pump value = 1.8*10^-1 mbar

The 5 prefilters for the SBox have been changed and at the same time a cleaning of the visible part of the motor was done using tissue and alcohol.

For a start they were cleaned using Vacuum cleaner , to be cleaned later using water

A timetable was placed with the date of the change and the next expected one.

On Friday, when placing the mirror in the mount inside the cavity, the mirror is fixed using a ring with 3 screws

one of the screws fell through the holes connecting the breadboard to the box (managed to remove it, but there was a lot of dust and metal particles left after)

cleaned the inside of the box, careful in the future.

There are only 3 for each mirror, it seems there are no spares. Careful not to lose them

this morning, the photodiode from the fiber coupling was only at 17mV (it was 40mV before the Christmas holidays).
after global realignment (infjection and CVBG !) we are back to 40mV which corresponds to 0.83mW into the 1st stage of the amplifier.

one added a photodiode (with one ND) after the OneFive, using a parasitic reflexion of the 1st PBS (the one used to work as an isolator), to monitor its power.
2.6V on 1Mohms <=> 47mW directly at the output of the OneFive

the beam coming back from the CVBG seems badly aligned with the 2nd PBS... its realignement could be a way to gain a little power for the future
 

The fiber connected to the 2nd stage photodiode was broken.
Thus, one connected the Auxilary output which is placed on the front cover, coming from a 10% tap of the 2nd stage, with a fiber to this photodiode.
for that, one drilled a small hole on the side to the crate to let the fiber in.

as the power is quite big, the 2nd stage photodiode is used with a filter to avoid its saturation.
one used also a 1kohms resistor to connect it to the scope.
one get more than 65mV when the output of the amplifier with only 2nd stage is about 350mW.
after about 30 minutes, the power increases slowly to more than 550mW.

summary :
- photodiode from the fiber coupling should read more than 60mV on 1kohms
- photodiode from the 1st amplifier stage should read more than 200mV on 50ohms
- photodiode from the 2nd amplifier stage should read more than 65mV on 1kohms

Today with Titouan, we installed a 10-90% fiber coupler between the EOM and the amplifier to have a diagnostic of the fiber injection power level.

65mV on 1kohms on the diagnostic photodiode is equivalent to 1.3mW injected to the 1st stage of the amplifier.
One has to get at least 50mV on the photodiode to inject 1mW to the 1st stage of the amplifier.

we used the included 1st stage photodiode which has to be above 200mV on 50 ohms.
one has 250mV on this photodiode

the 2nd stage photodiode seems to be broken.
one can use an internal tap for diagnotic or open the amplifier box and try to fix the photodiode.
to be done...

Yesterday, we installled again the chillers for the 2nd and 3rd stages of the 50W laser amplifier.

We changed the 2nd stage chiller tube connections by a press-fit connection which is almost leakage-free and much more convenient.

We shortened also the tubes and set the temperature to 19°C.

We tested that the setup is ok for temperature and leakage free.

The power reflected by the CVBG after the PBS is measured at 8.16mW (powermeter without AA-OD1 filter)

The power injected in a unpolarized fiber is about 5.4mW

The power injected in the EOM fiber (to be directly connected to the amplifier) is 1.5mW (1.72mW if a lambda/2 is added and 1.76mW if both lambda/2 and lambda/4 are added)

One has to check the spectrum after EOM to be sure it is clean (without CW peak)

Frep et CEP motors action has no effect on the spectrum central wavelength.

See the plot of the total OneFive spectrum (in black) and the part reflected by the CVBG (in red)
only 9.38% is reflected.

Thus, with 54mW of power for the total spectrum, one can expect no more than 5.06 mW before injecting in fiber and go through EOM.
One has to get more than 1mW before the amplifier.

CVBG has been installed but reflected power is much lower than before (new power in black with OD1 filter, old power in red... see attached fiber injection scheme)

it seems the OneFive spectrum shifted a lot with 40mW of output power. the center wavelength is roughly 1028.5 nm, thus the CVBG reflection is lower than before as it is much more shifted than before.

as the OneFive output power is low AND wavelength shifted, one used the IACT potentiometer to adjust the pump current.
the voltage at the begining of the operation was 0.35V and it is now 0.6V
the output power is now around 70mW as before.

One has to measure the optical spectrum...

the optical spectrum was exhibiting a strong peak... so one reduced the IACT value to remove the peak... the output power is about 54 mW but the spectrum is still shifted.
one has to use the Frep and CEP motors to see if we can recenter the spectrum.

No optical isolator available.
One used a half waveplate, a PBS, a faraday rotator and a PBS on a rotating mount to build an optical isolator.
the global transmission measured with powermeter equiped with AA-OD1 filter is 3.68 mW

One has to find a way the measure the isolation efficiency !

SBOX table cleaned and Origami 133MHz laser installed.

power measurement with powermeter and AA-OD1 filter (factor 10 of attenuation) = 3.88 mW

Electronic:
EOM photoline NIR-MPX-LN-10, S/N: 2559-22 x1
EOM newfocus free space 5 MHz IR, model H063-M x1
DET 25 AL/M x1
DET 10 C/M x1
DET 10 A/M x3
DET 36 A/M x4

Mirrors:
Output coupler 1/2 inch PR 99% MINICAV x10
Output coupler 1/2 inch PR 99.9% MINICAV x9
Fused silica plane 1/2 inch PR >99.997% MINICAV x9
Fused silica pl-cc 1/2 inch PR >99>997% MINICAV x8
Melles Griot trans=134 ppm, R>99.5% (plan?) Optics & Photonics x1
Melles Griot  trans=134ppm, R>99.5% (concave?) Optics & Photonics x2
Mirrors finesse 40k (old S-BOX ?) x3
Mirrors ThomX x4
Mirrors finesse 3k x4
Mirrors KEK
Mirror mighty laser spherical 0.5m trans=19ppm @1035ppm x1
Mirror mighty laser spherical 0.5m trans=10ppm @1035ppm x1

Other optics:
Window @1030 nm x6
Fiber pump diode 3rd stage amplifier S-BOX ~8m
MIR pick-up type 1 HR, AR x3
MIR pick-up type 2 no coating x4
Pulse picker SiO2 high damage threshold1030-1064nm x1
Lambda/2 HP @1030nm x2
Glan laser HP @1030nm x1
Lambda/4 HP @1030nm x 4
Large Bragg grating + mount v1000
+ several basic optical mounts

Mounts:
Aluminium S-BOX mounts
KEK mounts

Electronic:
EOM photoline NIR-MPX-LN-10, S/N: 2559-22 x1
EOM newfocus free space 5 MHz IR, model H063-M x1

the attched image is the plot of the datas from two high power experiments,

- the blue curve is from the high power experiment on 12/09/2018, injecting laser power is 27W, power inside cavity dropped from 157kW to 138kW in 33 min, during the 33min, no high order mode appeared, the two zooms of the blue curve just to show that they are un lock of the cavity but not high order mode;

- the red curve is from the high power experiment on 14/09/2018, we increased injecting laser power to 41W, the power inside cavity dropped from 205kW to 197kW in 30min, no un lock and no high order mode appeared.

first entry in logbook