Participaint: Aritomi, Chienming Eleonora, Shurong and Yuhang

Since I reported the beam parameter has been changed after we did the mode matching of SHG. So we measured the beam coming out again and we decided to recover the beam before BS to recover the situation as before. (The BS we talk here is where the beam is seperated and goes to FC or GRMC seperately)

We put a 150mm lens 9 holes before the first measurement point(3, 17).(now between SHG and measurement point, there is a 200mm 13.8 holes before the first measurement point already there). We dismounted the second lens after SHG to have space measuring beam parameter. The measurement region is between a steering mirror and EOM. The measurement result is shown below.

326, 588, 914, 1165, 1477, 1779, 2090

364, 676, 1018, 1296, 1623, 1921, 2210

The fit result is shown in the first attached figure. Then we use this result to trace back beam to SHG. This trace back process is shown in the attached figure 2. This is an important result, the beam waist size is 36um inside SHG.

Then we used this SHG new waist size and the current set-up to propogate it to the waist around BS. Because we have the measurement we did before to compare. We found the beam waist before was 26um. But now according to the measurement and some necessary simulation, the waist size now is 32um. Since it is close to our good value, we foresee the recover of mode matching by moving only the second lens.

The recover is done by looking at camera image and pd spectrum together. At the beginning, we found the pitch alignment is quite large, we recovered this degree of freedom first. Then we clean and center all the steering mirrors and lenses going to mach-zender. By keeping the TEM00 on camera and maximazing it, the alignment is recovered. Now the green mode cleaner is recovered.