Design study of the KAGRA output mode-cleaner

TL;DR

This paper presents numerical simulation results verifying that the KAGRA gravitational-wave detector's output mode-cleaner design meets the stringent filtering requirements, especially considering the minimal reference light used to reduce quantum noise.

Contribution

The study demonstrates that the current OMC design for KAGRA satisfies filtering requirements through detailed numerical simulations with realistic mirror surface maps.

Findings

The OMC design meets filtering requirements for KAGRA.

Simulations used realistic mirror surface quality.

The design effectively balances filtering and signal transmission.

Abstract

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 asymmetric 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.