Performance of a 1200m long suspended Fabry-Perot cavity

TL;DR

This paper reports on the successful construction and stabilization of a 1200m long Fabry-Perot cavity using GEO600 components, demonstrating stable operation and effective frequency stabilization for gravitational wave detection.

Contribution

First implementation and testing of a 1200m long Fabry-Perot cavity with stable control systems in a gravitational wave detector setup.

Findings

Achieved residual mirror displacement of about 150 nm rms.

Reached an error point frequency noise of 0.1 mHz/√Hz at 100 Hz.

Demonstrated stable operation over multiple 10-hour periods.

Abstract

Using one arm of the Michelson interferometer and the power recycling mirror of the interferometric gravitational wave detector GEO600, we created a Fabry-Perot cavity with a length of 1200 m. The main purpose of this experiment was to gather first experience with the main optics, its suspensions and the corresponding control systems. The residual displacement of a main mirror is about 150 nm rms. By stabilising the length of the 1200 m long cavity to the pre-stabilised laser beam we achieved an error point frequency noise of 0.1 mHz/sqrt(Hz) at 100 Hz Fourier frequency. In addition we demonstrated the reliable performance of all included subsystems by several 10-hour-periods of continuous stable operation. Thus the full frequency stabilisation scheme for GEO600 was successfully tested.