Introduction to gravitational wave detection.

Shematic view of Laser Interferometrer Gravitational Wave Detector.

Interferometric detectors are regarded as promising devices for gravitational wave detection. Since the effects of gravitational waves appear as a fluctuation of optical path length, it is required to detect the phase differences between two orthogonal light paths of a Michelson type interferometer. To achieve a sensitive detection, a method called "RF Dark Fringe Locking" is generally used. Phase modulation applied by Electro-Optic(EO) modulators the interferometer move the measurement band to high frequencies. To realize a long optical path length in the interferometer, a multi-pass geometry called optical delay-line or Fabry-Perot cavity is used. One of the interfering output beams is detected by a photo detector, and its intensity is held to a minimum of interference(dark fringe) by a servo system.