Virgo Logbook

Reports 1-1 of 1

AdV-COM (AdV commissioning (1st part) )

Allocca, Hardwick - 23:03 Monday 25 June 2018 (41984)

Cavity scans

In order to better analyze the arms mode content, we performed a cavity scan for each arm in "cold" mirror condition: indeed, the two arms have been unlocked for the whole weekend. Today, we only had a 1 hour-ish lock in dark fringe, and during this time the TMs didn't have the time to fully thermalize. So we can consider the mirrors "cold" enough.

Moreover, in order to better highlight HOMs, we intentionally misaligned a bit the cavity, and we reduced the 6MHz modulation depth as much as the RFC lock allowed (3dBm).

GPS North arm: 1213982458

GPS West arm: 1213981652

Analysis will follow

Comments to this report:

Allocca - 16:38 Thursday 26 July 2018 (42224)

From a closer look to the cavity scans, it seems that the main HOMs visible in the FSR belong to the sidebands, mostly from the 8MHz, whose modulation depth had not been decreased. In figure 1, one FSR of the North arm is shown: first subplot is the transmitted power, following subplots are 8MHz, 6MHz and 56MHz respectively. In figure 2, the same plot for the West arm is shown.

To measure the carrier HOMs ALL the modulation depth must be decreased (as much as possible, as not to unlock the RFC), and the mutual misalignment between arm cavity and input beam has to be further increased in order to enhance HOMs.

Images attached to this comment