Ellie, Evan and Dave It has been noticed that the H1 Inteferometer has a tendency to spatial mode-hope between TEMOO and TEMO1 modes whilst L1 does not have this tendency. We have been setting up to characterize the SRC cavity length and Gouy phase to see whether it differs from the design settings. To do this we set-up the auxillary laser and improved the focusing of the light onto the high speed 1611 diode of ISCT6 on the OMC_REFl_Air periscope. As a first step we repeated the previous measurement describe in AlOG 16084 with considerably higher signal to noise. With a bright Michelson lock we observed the reflection maximum on the either side of the Michelson. By eyeballing this data we can see that these occurred at -790+/-10 MHz and 905 +/- 10 MHz. Assuming that these are difference because of an offset in lock. The Michelson Reflection Dip is peaked at 847 MHz +/- 7 MHz. This corresponds to a Schnupp Asymetry = 8.9 cm +/- 1mm. A more rigorous analysis of this data will follow.
Here is a simple parabolic fit to the data, which sets the Schnupp asymmetry to 8.7cm (with an error of +/- 0.2mm. This error is calculated using error propagation of least-squares fitting with cross-correlation terms included, but it seems likely this statistical analysis underrepresenting the true error.) The upper- and lower- zero crossings are at 806MHz and 917MHz. Last December we measured Scnipp asymmetry at 9.05cm.
Improvements to this could be made by: -Measureing cable loss/frequency response (the beat note on IOT2R is fed to ISCT6 with a looong cable), -Correcting for photodiode frequency response curve, -Checking if auxiliary laser power has a frequency dependence.
We have removed the 1611 photodiode frequency response from the data and refitted the beat-note minima. We calculate a revised Schnupp asymmetry of 8.9cm (with an error of 0.1mm, which was calculated using least squares fitting error propagation with cross-correlation terms included).
