Wave-front distortion in laser-interferometric gravitational-wave detectors

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Abstract
We discuss the limitations placed upon the sensitivity of laser-interferometric gravitational-wave detectors by imperfections in the shape or alignment of the optics, for various different detector configurations. Wave-front distortion is seen to be a serious problem for interferometers which recycle only the light power. We suggest that the use of dual recycling can confer greater tolerance of distortion, and therefore better gravitational-wave sensitivity, upon an interferometer. This suggestion is backed up with results from an experimental implementation of dual recycling. However, in its simple form, dual recycling only helps significantly when the signal bandwidth is narrowed. We propose a new optical arrangement, dual recycling with a compound mirror, which gives greater tolerance of distortion without restricting the bandwidth. This may improve the sensitivity of future gravitational-wave detectors by a factor as high as 5, while at the same time improving their operational flexibility.