Triple Michelson Interferometer for a Third-Generation Gravitational Wave Detector

The upcoming European design study ‘Einstein gravitational wave Telescope’ represents the first step towards a substantial, international effort for the design of a third-generation interferometric gravitational wave detector. It is generally believed that third generation instruments cannot be installed into existing infrastructures but will require a new search for optimal detector sites. Consequently, the detector design will be subject to fewer constraints than the ongoing design of the second generation instruments. In particular, it will be prudent to investigate alternatives to the traditional L-shaped Michelson interferometer. In this article, we review an old proposal to use three Michelson interferometers in a triangular configuration. We use this example of a triple Michelson interferometer to clarify the terminology and will put this idea into the context of more recent research on interferometer technologies. Furthermore the benefits of a triangular detector will be used to motivate this design as a good starting point for a more detailed research effort towards a third-generation gravitational wave detector. PACS numbers: 04.80.Nn, 07.60.Ly, 95.75.Kk, 95.55.Ym