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'

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.

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

The previous Sbox telescope was dismantled and the mechanical components cleaned.

its lenses are still in the mounts, it looks that two of them are spherical and two are cylindrical

2 are -100 mm and 2 are +150 mm, there is also a box containing fused silica lenses that could be used.

Note: at high power use only fused silica lenses not BK7 type

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 was measured using a method called  "Focal Length Divergence Measurement Method"

Where a lens of a known focal length is placed on the beam path and the beam waist is measured at the focal distance using a beam profiler.

We ramped the power up to 10 W

for a focal length = 400 mm,

we measured a FWHM = 2.1 mm,

corresponding to a divergence = 4.45 mrad (edit : wrong software use)

for comparison, we measured the FWHM 8.1 mm  @ 1.55 m and extracted the divergence directly 4.46 mrad  (edit : this measurement is wrong - wrong use of the software) 

Note: better to use a lens of a focal lens higher than 100 mm (to reduce the error in the distance measured)

I placed a periscope to adjust the high of the beam from the amplifier output from ~ 10 cm from the table to ~ 15 cm

a dichroic mirror placed after it to reject the pump laser, all the mirrors on the path to the cavity were replaced with dielectric mirrors BB01-E03

the length of the path from the amplifier output to the cavity coupling mirror ~ 2 meters

setup defines the different optics placed in the path

Note: the beam goes all the way to the cavity, put it is not yet optimized to the irises.

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 .

Beam divergence was measured using a method called  "Focal Length Divergence Measurement Method"

Where a lens of a known focal length is placed on the beam path and the beam waist is measured at the focal distance using a beam profiler.

We ramped the power up to 10 W

for a focal length = 400 mm,

we measured a FWHM = 2.1 mm,

corresponding to a divergence = 4.45 mrad  (edit : wrong software use)

for comparison, we measured the FWHM 8.1 mm  @ 1.55 m and extracted the divergence directly 4.46 mrad  (edit : this measurement is wrong - wrong use of the software)

Note: better to use a lens of a focal lens higher than 100 mm (to reduce the error in the distance measured)

Here is a view of beam propagation in the optical software : GaussianBeam

the red filled shape is the model of the CELIA amplifier beam propagation with a divergence of 4.46 mrad
(the 2 black dots is the measurement of the beam size without any lens to change the beam propagation).

the 2 black lines have been put at the input and output cavity mirrors position relative to the CELIA amplifier position, respectively 2m and 2.7m roughly.
the cavity mode radius should be 0.55mm and 0.7mm respectively.
the cavity mode shape is represented by the 2 red lines (very close to the red filled shape which is the beam).

the most simple working telescope could be a +250 lens at 280mm from the CELIA amplifier.
it gives a beam radius of 0.53mm at the input mirror and 0.64mm at the output mirror.
the overlapping is more than 99%

the 2nd file is the GaussianBeam file.
 

Note the correct beam divergence is approximately ~ 2.3 mrad

M2 = 1.1 in this fit, but it is not yet optimized !!!!! could be reason for not accurate telescope reading.

Have tInstalled a new telescope with lenses

250 mm @ 86.8 cm from amplifier ,

-150 mm @109 cm (~ 22 cm between lenses)

the beam waist measured at a point on the reflection which is relatively the same distance to the injection mirror and the beam was much smaller than before

@ ~ 2 meters from amplifier + telescope ,  FWHM = 1.2 mm ,  waist = 0.85 * FWHM = 1.02 mm

Am adjustment on the lenses position to have a smaller waist.

+ 250 mm @ 88 cm from amplifier

-150 mm @ 111 cm from amplifier

the overlap with this placement is ~ 91%

the measured beam FWHM at the injection point M1 estimated to be ~ 0.94 mm

waist = 0.85*0.94 = 0.79 mm , it is still much larger than the needed 0.58 mm radius waist.

There is an improvement in reducing higher order modes, but the fundamental is still too weak to see, we observe higher order even modes 11 , 44 , ...

Today we managed to observe the fundamental mode and stabilize the scan on it until we improved the alignment enough.

We see some coupling, but it is very week < 5% , We improved the alignment and the polarization, but there is still no explanation to why it is very low.

The mode shape is circular with radius = 0.89 mm at transmission point, ~ 40 cm from circular mirror.

One EOM was installed along the injection into the amplifier, we saw a drop in the power measured by the first stage monitor from ~ 8.2 mW to 7.2 mW

we improved the injection up to 7.6 mW, but it still fluctuates a lot. We need to be careful about it.

The error signal looks clean, but it is very week which is due to the weak coupling.

Today, we played on the CEP but using the I-tune input of the Menhir Laser (+/- 5V maximal range).

unfortunately, one only saw a very weak improvement of the transmission by 10-20%... and the coupling improvement is almost zero.

the best improvement was for the maximal I-tune range (+5V) which maybe means that we could improve more the effect if were able to get a full range of 2pi for the CEP (instead of the present pi/2 range).