The response of laser interferometric gravitational wave detectors beyond the eikonal equation

The response of Michelson interferometers to weak plane gravitational waves is computed at one order accuracy beyond the eikonal equation. modulation electromagnetic field amplitude and polarisation are taken into account by solving transport equations geometrical optics with boundary conditions adapted laser interferometry. Considering both DC balanced homodyne readout schemes, explicit formulae for interferometer output signals derived. These comprise perturbations optical path length, frequency amplitude, shown be insensitive perturbations.