Sheila, Stefan

The low-finesse cavity made it non-trivial to set the demod phase correctly. Today we used the trick that any Q-signal disappears when the side-band is exactly anti-resonant. We then made an interpolation table to set the phase accurately within about 0.5nsec (~5deg) at any frequency.

1) First we identified the frequencies at which side-band and carrier are co-resonant (no demod signal):
   The 621st co-resonance we found experimentally at 23'303'644Hz, the 681st co-resonance at 25'555'116Hz. Fitting this to line up we get an FSR of about 37525.93Hz +-0.1Hz, or an arm length of 3994.47m +-1cm. Compare this to Daniel's alog: 3994.485m. (And I swear I did the error analysis before seeing Daniel's number.)

2) Next we hit the frequencies where the side-band is exactly anti-resonant, and phased the signal there. The delay numbers correspond to the phase shifter setting, assuming the delay is in with the switch up (i.e. 16.5nsec = 16sec and 1/2nsec switches up, rest down).
   23.922799MHz    31.5000nsec
   24.147946MHz    26.5000nsec
   24.260520MHz    23.3125nsec
   24.373093MHz    20.0000nsec
   24.448142MHz    18.1875nsec
   24.560716MHz    15.5000nsec
   24.785863MHz    10.5000nsec