Komori, Ushiba, Tanaka

### Abstract

We measured the IMC FSR by tuning the MIF sideband LO frequency.

The measured the FSR was 5.624378633 MHz and the estimated IMC absolute length was 53.302325(8) m

### What we did

• Following the procedure in klog23115, we set up the measurement configuration. Then we injected the excitation signal (1023 Hz, 1000 cnts) from DGCARM filter bank. We found the IMC transmitted power seems to fluctuate. So we decreased the excitation amplitude to 100 cnts.
• We tweeked LO frequency to find the best frequency where the peak in I signal was minimum for each REFL PD for each 1f sideband. The results were summarized in the following table.

• 	best
  REFL 45I	5.6243755500 MHz
  REFL 56I	5.624378400 MHz
  REFL 17I	5.62438200 MHz
  average	5.624378633 MHz

• Simirarly to klog23115, the difference of best frequencies for each sideband are larger than the measurement errors, we used the average value this time.
• Fig. 1 shows the spectra of I and Q signal from each sideband.

From each best frequency, we estimated each IMC absolute length and averaged them. We obtained the length = 53.302325(8) m