Now the Faraday is located 10~14 holes after PBS, according to the measurement of beam parameter we could predict the beam size at both ends of this Faraday isolator. The result is shown in the attached figure 1. I also checked the aperture of FI(IO-3-1064-VHP), which is 2.7mm in diameter.

In this case, the FI aperture and beam size ratio is minimum as 2.7/0.945/2 = 1.4286. We could calculate the Gaussian beam power through an aperture is P/P0 = 1-e^(-2*(1.4286)^2) = 0.98. So in our current case, even the best-aligned beam will loss 2% of the incident power. Also, I remember that we achieved almost 97% of power transmission of FI even in the case of this beam clipping issue.

Usually, we make the beam five times smaller than the aperture. But it is really difficult to have space and meet this usual requirement. However, if we move this beam one and a half hole backward, the power cut by aperture will be 0.5%. This can be realized by moving the fork of green injection mirror (the last green mirror before going inside the chamber). Because this is blocking the way of moving backward.