[Nakano, Aso, Lucia, Okutomi]

• We once lifted up the height of the payload by moving the F3 GAS fishing rod.
  • Other fishing rods in F1 and F2 seems not so smooth compared to the F3 GAS in the lifting-up operation.
• But after the height adjustment raising by 2 mm, we found a strange fluctuation in TM_OPLEV_{LEN, TILT}_SUM.
  • This 2 mm was confirmed in the BF V DC readout.
  • The fluctuation in the oplev sums looks oscillating at a suspension-like frequency such as ~ 1 Hz.
  • At this moment, the amplitude of the sum fluctuation was a few tens of counts in peak to peak.
  • This fluctuation was not resolved even at the height of 1 mm from the initial position.
  • It was difficult to accomplish the interferometer lock in this situation.
• In order to avoid this strange oplev behavior, we finally recover almost the original height of the payload.
  • To say exactly, the height was slightly raised by ~ 200 um.
  • Now it looks the fluctuation of the oplev sum decreased to a reasonable level like less than 10 counts in its amplitude.