A couple people asked today if Pcal calibration lines could be contributing to any of the noise humps. We have tested this previously, (recent LHO aLOGs 31101 and 31035). I looked at the time last night when we shuttered the Pcal Y laser (LHO aLOG 31991).

Attached are power spectra from a few minutes before shuttering, and just after shuttering for the four Pcal Y lines. In blue is the reference time just before shuttering, while red is the time just after shuttering. Observe that the blue Pcal line frequencies (7.9 Hz, 36.7 Hz, 331.9 Hz, and 1083.7 Hz) disappear, but the noise humps around 330 Hz and 1080 Hz remain.

In addition, as noted in LHO aLOG 31991, the glitch rate remained the same during this test.

Conclusions: Pcal does not contribute to the glitching observed in DELTAL_EXTERNAL, and Pcal does not contribute to noise humps at ~330 Hz and ~1080 Hz (laser on versus off comparisons again confirm these).