stefan.ballmer@LIGO.ORG - posted 17:45, Saturday 06 July 2013 - last comment - 18:42, Saturday 06 July 2013(6994)
Will the true 00-mode please stand up!
(Daniel, Stefan) Based on yesterday's mode scan we identified where the 00 mode should be (tiny peak, with transverse modes spaced at 17890Hz to the right). We did a dither alignment, first green (moving TMSY, ITMX and ETMX), then locked on the now identified 00-mode (moving PR2 and IM4). That gave us 500 cts in the transmission quad sum (up from 250 counts). Attached is the mode scan after the alignment.
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We also used the opportunity of having measured the 00 mode offset frequency in a grossly misaligned state. We can set a limit on the effecy of alignment on frequency offsets. 00-mode in grossly misaligned state (yesterday): -22842Hz 00-mode in aligned state (today): -22856Hz The difference is only 14Hz. Given that both numbers were derived by finding the top of the fringe with about 10Hz RMS fluctuations, the error in that measurement is also about 14Hz.