Today a second reading of the beam profile was done , with Victor ,Ronic, Aurlien and Manar

an additional set-up was made using two 4 deg wedges instead of High reflecting (HR) and Anti-reflecting (AR) mirrors.

Two reading were taken:

• at the output of the compressor with a NE30A filter on the beam profiler
• at the output of the amplifier with NE30A + NE10A filter on beam profiler

Readings of the beam shape and horizontal (upper plot) and vertical (lower plot) axis fit at the direct output of the amplifier.

The beam shape relatively shaped like an egg.

Readings of the beam shape and fit at the output of the compressor

differance from previous reading is that here we used wedges instead of HR mirrors.

Similar to previous readings, the beam shape deforms and the Gaussian fit is bad after 50% amplification

Adding the readings  20% , 30% ,  40%  for output of amplifier after the compressor

This Morning, another reading was taken for the output of the amplifier after the compressor using 2 wedge mirrors.

In addition, a start of the calibration of a PulseCheck "Autocorrelator" to measure the pulse duration. 

note, the pulsed laser used is OneFive 133.33 MHz

The pulse duration from the amplifier compressor output will be measured using PulseCheck autocorelator

a first alignment of the device was done, continuation in the afternoon.

YouTube link attached of the general operation of pulse check < 5 min :  https://www.youtube.com/watch?v=J1pNHYySSYg

Measurement of the pulse was done at the end of the afternoon, Pulse Duration FWHM = 12.9 ps

After a long process of adjusting the alignment and angle of the crystal inside the device

The power input on the PulseCheck device should be above the sensitivity, in our case we had 1 mW input.

To reach it, we removed one of the wedge mirrors and used dielectric mirrors with an amplification of 20% ~ 25 W direct output power.

The input to the pulsecheck must be horizontally polarized, which is why we used a polarizing beam splitter (PBS).

For a better pulse shape, Victor adjusted the "beam distance" and  "beam focus" nobs on the device.

Pulse Duration FWHM = 12.9 ps

Victor, Ronic, Manar

Today  was dedicated to the study of the CVBG, and it's effect on the beam profile

we opened the box containing the 2 CVBGs : The 2CVBG are glued from the bottom on a copper surface .

Using the beam viwer, the beam line inside the two CVBG is not at the exact center but not at the edges too and not hitting the boarders.

From the sides you see two lines, one is reflection on the metal.

To observe the effect of the first CVBG by itself, we blocked the second reflection into the 2nd CVBG.

By placing the D-shaped mirror just at the entrance of the 2nd CVBG (there was just enough space to put it)

Beam Profiler + OD 10E + OD 30E + OD(not known) placed at ~ 1 m from the output of compressor.

We see clearly a much better circular shape of the beam and a better Gaussian fit,

only above 90% where we see the fit percentage going down to ~ 86% and on just the Horizontal Axis.

For better comparison ,

the measurements done previously with 2 CVBGs was done at ~ 30 cm and the one done on Friday was for 1 CVBG is at 1 m

so we did additional measurement for 2 CVBGs at 1 m, for 20 , 50 and 70 % amplification 

we clearly see the similar deformation at high power.

Conclusion : the effect is most likely coming from the 2nd CVBG

At 70 % victor optimized the horizontal axis for the injection mirror into 2nd CVBG , we see an improvement in the Gaussian fit on Horizontal and vertical axis of ~ 2%

Adding the schematic of the measurements.,

the 4° Beam Deviation, AR Coating ( B coating)

The 3 data points taken of the beam profile are fitted in Gaussian Beam with taking the beam waist at the output of the compressor box.

Background is subtracted for all data points, the fit is more than 90% for all points.

a reading was observed with distance less than 200 cm before the periscope and the fit starts to degrade

reason probably be related to the bump beam !!! To be investigated by placing an iris.

This Morning with Victor the amplifier was turned on @ 20% amplification (output ~ 9 W ) for approximately 3 hours and no error appeared.

I took data of the beam profile at different points without a lens after the 2 wedges 

@ 0% (only pump beam), output ~ 300 mW (taken from previous data) , output after 2 wedges 2.2 uW  

@ 20% amplification , output ~ 9 W (taken from previous data) , output after 2 wedges 58.6 uW

fit to be added after processing the Beam Profiles data files.

Data with the lens to be taken !!

This morning, with Ronic, we opened the compressor box to observe if there is any misalignment of the mounts or the CVBG's

This morning we took data of the beam profile at 4 different points to see the evolution of

• the beam shape
• divergence

over distance for all amplification percentages

Data plotted for the distance vs radius for all and divergence in rad is extracted and plotted as a variation of amplification power.

Added is the Excel file with all the details and the PowerPoint for referance

Information about today's work is added to logBook !!

Today we tested a mirror from one patch

image is for the front face of the mirror

PowerPoint has more details about the images

Last week, with Ronic and Victor we aligned the cavity using CW laser (Koheras)

• we have also installed 4 mirrors in the cavity with the best theoretical qualities (serial number and images included)
  • The Plan ULE mirror P4 thickness was not compatible with the piezoelectric mount. We had to install a metal spacer behind the mirror to be able to fix it. the metal spacers in from ThorLabs made from INOX, It is 1 inch diameter (25.4 mm), we drilled a hole in the middle of 15 mm in the Workshop in bat 200. Then cleaned it using an ultrasound bath in pure water, using a small Ultrasound bath machine in Maverics platform Vide and Surfaces next to ThomX eglo.
  •  
  • This gives some difficulties in imaging the transmission at P4. To help with the imaging, we used the plastic #D printed irises that Yann made long time ago
  • we took images of the mode inside the cavity at P4 transmission.

• We also observed some oxidization on the metal bars of the controllers, more on the side of S2 and P4. we are yet to test the motion of the motors in the z-axis.
• Friday evening we closed the windows using a new copper rings (last one we have, Ronic placed a new order).
• The pump was turned on by Bruno and Eric yesterday afternoon. The current vacuum level is 6-7*10^-6 mbar

the pre and the turbo pimps are on so still too noisy to work, we have access all day tomorrow.

Today, we prepared lenses for a telescope for the CW laser injection into the cavity, yet to be installed

Image of the transmission at P4 attached, an estimation of the beam size of the mode see is ~ 5.5 mm 

The vacuum in the 2 optical cavities is decreasing but slowly. today it is 2.6 - 2.4 * 10^-7 mbar

Yesterday morning we locked the cavity on a strange mode in the cavity (we call it mode, but not sure what it is ??)

we also managed to lock on a higher order mode 02

we get an estimated 30% coupling (expected value), and note that we have not installed a telescope yet.

This morning with Daniele and Viktor,

- we confirmed the "potato" mode was well centered on the injected beam and was not due to some misalignment of the injected beam compared to the cavity axis.
we look at the reflected beam during a lock. we can see the direct reflected beam superposed with the cavity mode (cf attached image).

- then we assumed the "potato" mode problem could come from the too short distance between spherical mirrors which introduces ellipticity and finally can lead to some instability.
we manage to move further spherical mirrors S2 and S3 by moving them from 1 350 000 to 800 000 steps.
=> we increased the distance by 2x 550 000 steps (with 6µm for 1000 steps) => we increased the distance between spherical mirrors by 6.6 mm
the new mode shrinked a lot and at the end was spherical at 73%.
the mode size is now about 4400 x 6000 µm but with the major and minor axis still at 45° !