[Shih-Hong Hsu, Chia-Jui Chou, Hirotaka Yuzurihara, Yi Yang]

    In klog-33681, which was uploaded on 05/06, Ushiba-san updated the BS_TM_ACTALIGN matrix and thus reduced the MICH error signal between 4 Hz to 20 Hz.

    Also on 05/06, we found scattered light noise appearing in the MICH signal. The scattered light noise appeared in the frequency range below 20 Hz (Fig. 1). However, the typical scattered light noise in MICH signal was only seen above 20 Hz (Fig. 2). The occurrence of the arch-shape from scattered light noise is related to the motion of the noise source. The occurrence of the arch-shapes of scattered light noise on 05/06 MICH signal is about 0.436 Hz, which is close to the typical value of 0.43 Hz. (Fig. 3) 

    From the previous report, klog-33668, there may be a positive correlation between scattered light noise occurrence and the magnitude of seismic motion in 0.3 Hz to 1.0 Hz. The magnitude of seismic motion on 05/01 and 05/06 are similar (Fig. 4), but the amount of scattered light noise in 05/06 (~27 [labels/hr in lock]) is higher than in 05/01 (~6 [labels/hr in lock]). Also, from the fitted curve of April scattered light data (klog-33668, Fig. 1), the magnitude of seismic motion in 0.3 Hz to 1.0 Hz in 05/06 was about 0.1~0.15 um/s. The corresponding scattered light noise labels should be below 10 per hour.

    This may suggest that MICH signal could be more sensitive to the scattered light noise contamination in lower frequencies.

Fig. 1: GauCh of 05/06 16:00~17:00 MICH & an example of scattered light noise in 05/06

Fig. 2: GauCh of 04/29 03:00~04:00 MICH & an example of scattered light noise in 05/06

Fig. 3: Scattered light noise occurrence frequency calculated by the method mentioned in JGW-G2416109-v1

Fig. 4: Seismic motion in 033 Hz to 1 Hz for 05/01 and 05/06