Abstract

We analyse the response of laser interferometric gravitational wave detectors using the full Maxwell equations in curved spacetime in the presence of weak gravitational waves. Existence and uniqueness of solutions is ensured by setting up a suitable boundary value problem. This puts on solid ground previous approximate calculations. We find consistency with previous results obtained from eikonal expansions at the level of accuracy accessible to current gravitational wave detectors.

Highlights

  • The geometric optics equations arise at first order in eikonal expansions, where one explicitly introduces a frequency parameter ω and an eikonal function ψ, seeking solutions possessing a series expansion of the amplitude in inverse powers of ω [13]. The validity of such high-frequency approximations in the considered context has been questioned in [14], and some previous attempts to obtain formulae applicable for all incidence angles of the gravitational wave have led to expressions which are undefined if the gravitational waves (GWs) propagates parallelly to one of the interferometer arms [15, 16]

  • We confirm that a calculation of the interference pattern based on eikonal expansions, and on geometric optics, is consistent with Maxwell equations within the model analysed here, and provides the key information needed for current experiments

  • If there exists a corresponding solution of the Maxwell equations, this solution is unique and independent of the coordinates by an identical argument

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Summary

Introduction

Interferometric gravitational wave detectors are the only instruments so far that have been able to directly detect gravitational waves (GWs). The geometric optics equations arise at first order in eikonal expansions, where one explicitly introduces a frequency parameter ω and an eikonal function ψ, seeking solutions possessing a series expansion of the amplitude in inverse powers of ω [13] The validity of such high-frequency approximations in the considered context has been questioned in [14], and some previous attempts to obtain formulae applicable for all incidence angles of the gravitational wave have led to expressions which are undefined if the GW propagates parallelly to one of the interferometer arms [15, 16]. We confirm that a calculation of the interference pattern based on eikonal expansions, and on geometric optics, is consistent with Maxwell equations within the model analysed here, and provides the key information needed for current experiments.

A Boundary Value Problem for Maxwell’s Equations
Coordinate-Independence
Justification of Eikonal Expansions
The Setup
Scalar Waves
Emission From a Laser
General Expression for Emitted Waves
Emitted Scalar Wave
Reflection At a Mirror
General Expression for Reflected Waves
Reflected Scalar Wave
Maxwell’s Equations
The Unperturbed Field
Boundary Values
The Emitted Wave
Result
Reflection at a Mirror
The Reflected Wave
The Returning Field
Non-Polarising Beam Splitters
Output Field
Output Power
Low Frequency Limit
Comparison with Fibre Optics
Discussion

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