Most second-generation gravitational-wave detectors employ an optical resonator called an output mode-cleaner (OMC), which filters out junk light from the signal and the reference light, before it reaches the detection photodiode located at the asymm
etric port of the large-scale interferometer. The optical parameters of the OMC should be carefully chosen to satisfy the requirements to filter out unwanted light whilst transmitting the gravitational wave signal and reference light. The Japanese gravitational-wave detector KAGRA plans to use a very small amount of reference light to minimize the influence of quantum noise for gravitational waves from binary neutron stars, and hence the requirements to the OMC are more challenging than for other advanced detectors. In this paper, we present the result of numerical simulations, which verify that the OMC requirements are satisfied with the current design. We use the simulation program FINESSE and realistic mirror phase maps that have the same surface quality as the KAGRA test masses.
A comparison of analytic calculations and FINESSE simulations of interferometer responses to gravitational wave strain. The response to a gravitational wave is gradually built up from the effect of modulating a space by a gravitational wave to Sagnac
and Michelson interferometers with and without arm cavities. This document details the steps necessary to perform such simulations in FINESSE and explicitly derives the interferometer response equations.
Finesse is a fast interferometer simulation program. For a given optical setup, it computes the light field amplitudes at every point in the interferometer assuming a steady state. To do so, the interferometer description is translated into a set of
linear equations that are solved numerically. For convenience, a number of standard analyses can be performed automatically by the program, namely computing modulation-demodulation error signals, transfer functions, shot-noise-limited sensitivities, and beam shapes. Finesse can perform the analysis using the plane-wave approximation or Hermite-Gauss modes. The latter allows computation of the properties of optical systems like telescopes and the effects of mode matching and mirror angular positions.
Several km-scale gravitational-wave detectors have been constructed world wide. These instruments combine a number of advanced technologies to push the limits of precision length measurement. The core devices are laser interferometers of a new kind;
developed from the classical Michelson topology these interferometers integrate additional optical elements, which significantly change the properties of the optical system. Much of the design and analysis of these laser interferometers can be performed using well-known classical optical techniques; however, the complex optical layouts provide a new challenge. In this review we give a textbook-style introduction to the optical science required for the understanding of modern gravitational wave detectors, as well as other high-precision laser interferometers. In addition, we provide a number of examples for a freely available interferometer simulation software and encourage the reader to use these examples to gain hands-on experience with the discussed optical methods.
