Found the reason of astigmatism

Today the beam seems pretty low on the PR mirror, so we moved the pitch of the 2inch mirror first and aligned the beam everywhere, then we moved the input mirror bench about 2cm right to put the mirror in the right position.

With putting two aperture on the bench (pic 1), we set the position of the beam, and started to move the lens, at first when we just turn the screw in horizontal direction to center the beam on the lens, the beam is still elongated. Then we tried to turn the lens a little bit,then we found out the elongated changed to the vertical direction. If look at picture 2, it is not very obvious, but when we tried to send the beam far away, the beam is longer in the vertical direction a lot. We thought the reason of the beam shape is because of the large beam and short focal length(150mm), since the spherical aberration, when the beam pass the spherical surface, the light away from the axis does not focus on the same point as the light along the axis, so the more we off the center of the lens, the beam elongated more. So then we will try to center the beam better on the lens.

But the other strange thing is that the beam at 290m target is still elongated on horizontal direction(pic 3), this situation is the same when we tried to use the aperture to force the beam to beam round, then at the first target it looks good, but then on the second target it is pretty long in horizontal. We need to have a better beam and then try to find the possible reason of this.

The other things we discovered on Friday is that why when we center on all the mirror and also second target, we were off center of the first target. Then first target has a axial precession like the Earth's axis, so if we turn it to the other face it will be well centered also.