We have two iris inside filter cavity arm to check the direction of green laser beam. To make sure the beam can arrive at the filter cavity end mirror, we need to make the green beam hit on a point checked in the past when filter cavity is aligned.

Remember that, for the first step, we should make the green beam hit on several reference points on PR and BS chambers.

The first attached picture shows the beam position on the first iris. In this case, the iris needs to be rotated so that the stick is not visible (hidden on the back side of iris). At this moment, the beam position should be just above the hole.

For the first iris, when the stick is visible, the situation is shown in Fig. 2. At this moment, the beam is above the hole and located a bit the left side.

If the beam hits on the first iris like what is shown here, it should be not diffcult to find the green beam on the second iris. If not visible on the second iris, we should move the green beam around with little adjustment. Then what we need to do is to just make the green beam go through the hole of it.