Shishido, Hasegawa, Miyakawa, Kokeyama, Tomaru, Nakano, Enomoto, Capocasa, Yamamoto T, Yamamoto K, Izumi,

Today we succeeded in locking the (half) cryogenic Michelson interferometer for the first time.

The ETMY mirror was at the cryogenic temperature whereas the ETMX mirror was at the room temperature.

Configuration:

• REFLAIR_A_RF17_Q fedback to BS TM.
  • See the 2nd attachment.
• ETMY control:
  • MN oplev loop for YAW
  • MN T photo sensor damping
  • BF YAW control
• ETMX control:
  • BF YAW control only
• PR3 optical lever control was intentionally off (4768)
• Both ETMs had an angular fluctuation less than 1 urad today for both pitch and yaw.
• ETMX optical lever
  • P = 12 urad
  • Y = 1 urad
• ETMY optical lever (which was re-centered today at around noon)
  • P = 30
  • Y = -35

Some observations:

• We could hold the Michelson for 10 minutes.
• The lock stretch often ended with saturation in the BS DAC.
  • The rms is largely dominated by the 1.6 Hz component (see the 3rd attachment) which had high coherence with the ETMY pitch and yaw.
  • Once saturates, it causes a large angular kick on the BS leading to momentary unlock.
• The UFG for the moment was measured to be approximately 8 Hz as seen in the 4th attachment.
• The visibility [ (Cmin-Cmax) / (Cmin +Cmax) ] at the REFL port was found to be about 70%. See the 1st attachment.
  • Note that the EX gate valeve is still closed.

Next things:

• More precise analysis of the open loop transfer function.
• Measurement of the IM longitudinal response of the BS.
• Design of the hierarchical control with the IM and TM stages.