Length sensing and control strategies for the LCGT interferometer

The optical readout scheme for the length degrees of freedom of the LCGT interferometer is proposed. The control scheme is compatible with both the broadband and the detuned operations of the interferometer. Interferometer simulations using a simulation software Optickle show that the sensing noise couplings caused by the feedback control can be reduced below the target sensitivity of LCGT with the use of feed-forward. In order to improve the duty cycle of the detector, a robust lock-acquisition scheme using auxiliary lasers will be used. (paper)