Prospects for High-Frequency Gravitational-Wave Detection with GEO600

We investigate whether the GEO600 interferometer can be sensitive to gravitational waves in the kilohertz frequency range. Typically, most ground-based interferometers are optimized for sensitivity around 200 Hz. Interferometric detectors also feature narrow bands of strong sensitivity where the sideband fields created by a GW are resonant in the optical system. GEO's short arms and lack of Fabry-Perot cavities make it a sensitive interferometer at high frequencies. With just small changes to system parameters, such as the detuning of the signal recycling mirror, the narrow band of high sensitivity can be scanned over a much larger range of frequencies. Using Finesse 3.0, we compute a noise budget for GEO600 across a frequency range from several kHz to tens of kHz for various detuning angles. We investigate the sensitivity of GEO600 to ultralight boson clouds and sub-solar mass primordial black hole mergers, and compare its ability to detect these sources to that of other ground-based interferometers.