An optical cavity consisting of optically trapped mirrors makes a resonant bar that can be stiffer than diamond. A limitation of the stiffness arises in the length of the optical bar as a consequence of the finite light speed. High laser power and li
ght mass mirrors are essential for realization of a long and stiff optical bar that can be useful for example in the gravitational-wave detector aiming at the observation of a signal from neutron-star collisions, supernovae, etc. In this letter, we introduce a parametric signal amplification scheme that realizes the long and stiff optical bar without the need to increase the laser power.
The third generation of gravitational wave observatories, aiming to provide 100 times better sensitivity than currently operating interferometers, is expected to establish the evolving field of gravitational wave astronomy. A key element for achievin
g the ambitious sensitivity goal is the exploration of new interferometer geometries, topologies and configurations. In this article we review the current status of the ongoing design work for third-generation gravitational wave observatories. The main focus is set on the evaluation of the detector geometry and detector topology. In addition we discuss some promising detector configurations and potential noise reduction schemes.
