Classical ground based interferometry

The current ground based interferometic gravitational-wave detectors are Michelson type interferometers with arm lengths in the km range. The sensitivity is limited by influences that either change the real physical arm length (typically seismic noise moving the mirrors or thermal noise moving the mirror surfaces) or by by noise sources that cause an apparent change of the arm lengths (e.g., shot noise). The first generation of most detectors is built on prototype-tested technology, using power and signal recycling, active damping and multiple-stage pendulum suspensions. Over the last decades ground-based interferometric gravitational-wave detectors have evolved to sensitivities where extended periods of data taking yield realistic chances to find gravitational waves within the data.

Current and future experimental laboratory work will be devoted to the next generation of more sensitive interferometric gravitational wave detectors. To reduce shot noise, one has to increase the light power in the interferometer which creates problems with transmissive optics. One solution to this problem could be reflective interferometer topologies where micro- and nano-structured optics like gratings offer new potential. Substrates can then be chosen from a much wider variety of also opaque materials. Then laser powers of 1 MW may be coupled into arm cavities built from mirrors at cryogenic temperatures. The goal of this research is to fabricate and prototype grating optics of gravitational-wave detector scale as well as to demonstrate servo control schemes of supended grating coupled cavities.