How an interferometer extracts and amplifies power from a gravitational wave

The operation of an interferometric gravitational wave detector is described in terms of the power flow through the device. I show how to identify the mechanical power absorbed by the interferometer from the gravitational wave and describe the power gain provided by the interferometer using the classical theory of parametric transducers. I discuss the power relationships involved in the optical heterodyne process at the output photodiode. I compare various possible definitions of the cross section of an interferometer with the definition used in the description of a resonant-mass gravitational wave detector.