Notes on the OMC cavity alignment strategy
- x3=1.17 γ + 1.40 δ, x4=1.40 γ + 1.17 δ
- This means that the effect of the two curved mirrors (i.e. gouy phases) are very similar. To move x3 and x4 in common is easy, but to do differentially is not simple.
- 1div of a micrometer is 10um. This corresponds to the angular motion of 0.5mrad (10e-6/20e-3 = 5e-4). ~0.5mm spot motion.
- ~10um displacement of the mirror longitudinal position has infinitesimal effect on the FSR. Just use either micrometer (-x side).
- 1div of micrometer motion is just barely small enough to keep the cavity flashing. => Easier alignment recovery. Larger step causes longer time for the alignment recovery due to the loss of the flashes.
- After micrometer action, the first move should be done by the bottom mirror of the periscope. And this is the correct direction for beam walking.
- If x3 should be moved more than x4, use CM2, and vise versa.
- If you want to move x3 to +x and keep x4 at a certain place, 1) Move CM2 in (+). This moves x3 and x4 but x3>x4. 2) Compensate x4 by turning CM1 in (-). This returnes x4 to the original position (approximately), but leave x3 still moved. Remember the increment is <1div of a micrometer and everytime the cavity alignment is lost, recover it before loosing the flashes.