# Influence of non-uniformity in sapphire substrates for a gravitational wave telescope

## TL;DR

This paper investigates how non-uniformities in sapphire substrates affect the performance of a cryogenic gravitational-wave telescope, using simulations based on measured optical maps.

## Contribution

It introduces a simulation approach to assess the impact of sapphire substrate non-uniformity on gravitational-wave detector performance.

## Key findings

- Non-uniformity causes characteristic structures in transmission maps.
- Simulations show potential influence on interferometer sensitivity.
- Results inform substrate quality requirements for detectors.

## Abstract

Construction of a large-scale cryogenic gravitational-wave telescope KAGRA has been completed and the four sapphire test masses have been installed in cryostat vacuum chambers. It recently turned out that a sapphire substrate used for one of the input test masses shows a characteristic strcuture in its transmission map due to non-uniformity of the crystal. We performed an interferometer simulation to see the influence of the non-uniformity using measured transmission/reflection maps.