M.Yamamoto,Sato,K.Yamamoto,and Tanaka

Now we are investigating the Q-value of the elastic vibration in the Test Masses.

As a start, we re-measured the Q-value of the excited drumhead mode of ETMX.

(previous results: https://klog.icrr.u-tokyo.ac.jp/osl/?r=22780)

・Procedure

We sent the 24kHz excitation signal from the 64kHz DGS model to ETMX to excite ETMX drumhead mode.
and We connected a FFT analyzer to the monitor port of IQ demodulator of AS RFPD to measure the resonance of the excited drumhead mode
(The SR560 was inserted between the FFT analizer and the IQ monitor to clarify 
the drumhead mode peaks. 3kHz-30kHz Band pass filter and 10x gain were set with the SR560.).
After confirmed the peak of the resonance at drumhead mode,
We connected a lock-in amplifier to the IQ monitor to record the exact resonance frequency and decay time of the resonance
(the time constant of the lock-in amplifier was set to 50 ms and the sensitivity to 100 μV and the dynamic reserve to high).
The decay of the resonance was recorded from an oscilloscope connected to the output of the lock-in amplifier.

・Result

We confirmed a resonance peak at 23.6904 kHz.

We also confirmed that the resonance decays after turning off the drumhead mode excitation signal.

From fitting, the decay time was 1.5 seconds. And,From the ring-down method, the Q value of drumhead mode of ETMX was estimated to be 1.1×10^5.

The Q value of ETMX was 2.1×10^5 in the measurement on 2022/11/2.

We confirmed the same Q value as the previous measurement.

(The decay of the resonance with time and the fitting results(semilog graph)  are attached as figures.)

As a next plan, we would like to measure the Q value of the elastic vibration mode of other test masses other than ETMX.