The Speed-Meter Experiment

We are currently setting up a proof-of-principle experiment for a speed-meter, aiming to demonstrate that a Sagnac interferometer can outperform a Michelson interferometer with similar design parameters (such as mirror mass and optical power).

Comparison Michelson Sagnac

The plot on the right hand side shows the top level noise budgets of a Michelson and a comparable Sagnac interferometer, both featuring 1 gram test masses, arm cavities and a circulating optical power of 1kW. The plot illustrates the improvement in overall sensitivity (green area) that can be achieved by the Sagnac speed-meter over a Michelson interferometer with comparable parameters.

The optical layout of our Sagnac speed-meter interferometer consists of three main building blocks: The input and detection optics including homodyne detection (shown in green in the schematic drawing below), a central Sagnac interferometer (blue) and two high-finesse arm cavities (orange).

Schematic 1x

The experiment will be operated at room temperature, with fused-silica optics and a laser wavelength of 1064nm. The interferometer will be housed in two GEO-style vacuum chambers in which the two triangular arm cavities of the Speed-Meter interferometer will be aligned in parallel. The cavities will be approximately 1.3m long, featuring a 1.6 gram curved input mirror with a diameter of 0.5" and two plane far mirrors with a diameter of 1.5" each. The targeted circulating light power of 1kW in each arm cavity will be achieved by choosing a finesse for the arm cavities of approximately 10000. The planned core optics suspension design is based on double pendulum stages with a monolithic fused silica last stage for horizontal isolation and blade springs for vertical isolation. To avoid sensitivity of the interferometer to rotations, it will be arranged for the effective area enclosed by the beam paths to be zero. For signal readout, it is planned to employ balanced homodyne detection.

For more information, please contact Stefan Hild.