After our PSL work, we measured the cross-over frequency between PZT ans EOM loops to check the effect of the new amplifer. Fig.1 shows the Cross-over frequency, dark curve is the TF before the gain compensation, and bright curve is after compensation. Before the gain compensation, the cross-over frequency is about 9 kHz. According to klog35090, the original cross-over frequency was 10 kHz. However, this frequency is determined so that the 150 kHz peak in the OLTF of the IMC loop across the 0dB line. Now, the 150 kHz peak is already reduced thanks to the preper notch filter implementation. Therefore, we attempted to restore the value of the cross-over frequnecy to the one when we used a fiber amlified laser, 14 kHz by adjusting the related gains, IMC-SERVO_{IN1, FAST}GAIN. The bright curver in fig.1 is after adjustment. the current cross-over frequency is 14 kHz.

And then, we measured the OLTF of IMC loop (fig.2). the current UGF is around 150 kHz this value is higher than the previous value, 134 kHz, according to klog35177

we compensated IMC-SERVO_IN2GAIN and LSC-MCL gain to keep the cross-over frequency. However, the cross-over frequency between PZT and MCE is several dB higher than before although it is compensated, according to Ushiba-san.  Then, Ushiba-san adjusted the cross-over frequency. Fig. 3 is the cross over frequency after the adjustment.

After that, we confirmed that IFO can reach PRFPMI_RF_LOCKED state. However, the lock duration seems to be shorter than before.