(Daniel, Alexa)
Today we measured the EY cavity length. We repeated the technique described in alog 9626. We ran the measurement three times. And got the following results:
| Offset | Zero Crossing (MHz) | Length (m) |
| 0.0V | 24.992280 | 3994.4690 |
| 0.0V | 24.992281 | 3994.4688 |
| -2.5V | 24.992277 | 3994.4695 |
where the offset refers to the common offset in the PDH REFL servo board. The results of each attempt is plotted respectively. (I have also attached the data and the matlab script that creates the plots and gives the values listed in the above table). This gives:
Zero crossing freq = 24.992280MHz ± 5Hz
EY Arm Cavity Length = 3994.4691m ± .7mm
If we compare this to the result for EX, we find that the cavity lengths differ by 1 ± 1mm.
The nominal y-arm length according to Jason is 3994.4728 ± 0.004 m, about 3.7 mm off the measured value and well within the error bar.
The x-arm length can be found in alog 9626.