Direct measurement of the scattered light effect on the sensitivity in TAMA300

Laser interferometer gravitational wave detectors need vacuum tubes through which the laser beams pass. The light scattered from the arm cavity mirrors will make multiple reflections from the inside wall of the polished tube back onto the mirrors causing phase noise on the interferometer output beam. The TAMA300 has two 300 m length arms enclosed by vacuum tubes. By vibrating one of the tubes of the TAMA300, we directly observed the effect of the scattered light on the displacement sensitivity. It was found that a tube vibration amplitude of 5.6 {mu}m at 776.5 Hz increased the mirror displacement noise by 1.2x10{sup -17} m. This noise level is consistent with the calculated noise due to the scattered light effect.