Wavefront tilt correction system for MIRA-I.2

The outline and the performance of the wavefront tilt correction system for the Mitaka optical and InfraRed Array, MIRA-I.2, is reported. The tilt control system consists of quadrant detectors and PZT-driven tilt mirrors. These components are controlled by three computers connected via local area network system. The control loop frequency of 2660Hz is achieved and this high loop frequency enables the stable operation of the control system with a bandwidth of approximately 80Hz in open loop at 0dB. Preliminary results of one night observation of α Lyr showed that this system suppress the relative wavefront tilt of incoming lights to 0.46 arcsec while it is 1.9 arcsec without control. With an aperture size of 90 mm and the wavelength of 750 nm, this means the tilt control system improves the visibility loss to 9% while it is 89% without control.