I changed the lenses' position to modify the beam profile for HOMs, especially to make the beam width larger.
The target beam width was 500um though the initial beam width was ~200um.
To ahieve this beam size, I changed the lenses and their position as attached by monitoring beam profile.
I put f=-75mm and f=200mm lenses instead of f=-50 and f=150mm ones.
Then the beam width around AOMs became about 500um and it was beam waist.
After that, I played with STMs and maximize the diffraction efficiency (but not adjusted the alignment of AOM itself).
Eventually, the input power to AOM was 5.7mW and the 1st order diffraction power was 4.5mW which corresponded to ~80% diffraction efficiency.
Actually, the lens position was slightly disturbed when I clamped them.
So I will tune their position and adjust the alignment to maximize diffracted beam power as a next step.
Then I will put a PBS, QWP, and mirror to compose double-pass AOM configuration.
I tuned the lens position and alignment, then the diffracted beam power became 5.0mW which seemed to be enough (input power was 5.7mW).
Then I installed a PBS in front of the AOM, and adjusted the alignment.
At this moment, still the diffracted beam has 5.0mW.
Tomorrow, I gonna install convex lens and re-align the double-pass AOM.