Using the Ward-Fricke variant* of the Sigg-Frolov method, we found the length of the mode cleaner to be 27.0934020183 meters, a difference of -2.7mm from Andrey,
Keita, and Rana's measurement on August 30th.
The updated RF frequencies are:
3 fsr = 33 195 439 Hz
12 fsr = 132 781 756 Hz
15 fsr = 165 977 195 Hz
18 fsr = 199 172 634 Hz * We did the usual scheme of connecting a 20mVpp, 2 kHz sinusoid into MC AO. Instead of scanning the RF frequency by turning the dial on the 166 MHz signal generator ("marconi"), we connected a DAC channel into its external modulation port (set to 5000 Hz/volt FM deviation). We then scanned the RF frequency from the control room, minimizing the height of the 2 kHz line in LSC-PD11. In principle one could write a little dither servo to lock onto the 15fsr, but in practice simply cursoring the slider bar around while watching a dtt display worked just fine. |