As I replaced a lens in double-pass AOM path, I tweaked the position of the lens and the mirror.
Current lens is f=70mm one.
Since the transmitted flash could not see due to the poor mode matching, I tried to improve the mode matching.
The lenses were replaced and f=-75mm and f=300mm ones are put now.
Their positions are about 0.226m and 0.659m from the beam waist, respectively.
After that I could get beam size about 65um at its waist where it is reasonable position for the apex mirror of folded cavity.