misalignment and angular perturbation impact

participant: Tomura, yuhang

We measured the misalignment again by changing the driving frequency of AOM. The measurement shows it is around 0.168. And the standard deviation is 0.0165.(See attached picture 5) So the residual misalignment is 17% (+/-2%) .

Besides, we injected a sine-wave noise into the local control of optical lever. We choose the frequency of 20Hz, 200Hz and 500Hz. The amplitude is 1V. The noise is injected into EM (yaw and pitch). The 20Hz is appreciable on the transmission of green.(See attached picture 1)We are sure the noise is injecting to EM.(We can see it from the local control like picture2) And the frequency of the noise we are injecting is the same with the frequency we can see in the transmission signal of green light. At the same time, we measured the noise spectrum of error signal. We found it has no difference from the case without noise injecting.(For all the test, they have no difference. See picture 3 and 4)

This perturbation test may tell us that the angular to length coupling is low, so that its affect for error signal is below the present noise level.