[Ushiba, Yokozawa, Komori]

Abstract:

For the first time in KAGRA, we estimated the Q-values of two violin modes through ringdown measurements.
Both Q-values were found to be approximately 1.7e4, consistent with estimates derived from the line width in the DARM spectrum (Q=1.5e4).

Details:

We performed ringdown measurements to estimate the Q-values of violin modes and confirm that they are approximately 1e4, as expected due to thermo-elastic loss.
This estimation aligns with previous measurements based on the line width in the DARM spectrum.
As a first trial, we selected two violin modes of the ETMY.
Details of the excitation channel, the amplitude, the duration, and the measured channel will be reported later.

The resonant frequencies of the measured modes are 187.337 Hz and 189.716 Hz.
Figures 1 and 2 show the raw measured data (blue), the calculated envelope (red), and the fitted curve (green) for each mode.
From the fitted curves, both Q-values were estimated to be 1.7e4.

Figure 3 shows the DARM spectrum (blue) and the fitted curve (red).
Using the line width measurement, both Q-values were estimated to be 1.5e4, which is in good agreement with the results of the ringdown measurements.

Discussion and Future Plans:

The agreement between the ringdown and line width measurements is within 10% accuracy, suggesting that ringdown measurements may not be necessary for estimating violin Q-values.
Instead, these values can reliably be determined from the line width in the DARM spectrum.
To validate this conclusion, we plan to perform ringdown measurements for additional violin modes in the near future.