Lens adjusted and cavity locked again

After adjusting the second and third lenses little by little, we found out in the range they can move now is impossible to have a better mode matching for the cavity. Before the second lens there was a aperture to filter the other orders from AOM that we don't need, I tried to remove it and move the second lens towords the AOM, this time although the reflection beam still larger than the injection one, it has a reasonable size. So I left the lens there and tried to see if can use other apertures to cut the other orders.

So the aperture before the FI, the orders are not seperated enough there, the aperture after the FI, we can open a bit to let the beam go through it, but then the reflection beam will be cut. So finally we used the diaphragm we put in front of the window to do the fitler job, showed in the first picture.

One problem of this configuration is that all the orders pass through all the optics after AOM, actually since all the optics are aligned with the first order, so I think for the beam deformation maybe there will be no problem, but I am not sure if this will affect the FI.

After aligning everything and having a reasonable beam, we tried to lock the cavity again. Using the Stanford to amplify the PDH signal with gain of 10, the cavity can be locked again(pic 2), but not very stable. The alignment seems cannot improve more, so I think it is still have something to do with the mode matching.