Scattered light noise due to dust particles contamination in the vacuum pipes of the Einstein Telescope

TL;DR

This paper investigates how dust particles on vacuum pipe surfaces cause scattered light noise in the Einstein Telescope, offering guidelines to control particle contamination for optimal detector sensitivity.

Contribution

It provides a detailed analysis of light scattering by particles on surfaces and establishes cleanliness standards for the Einstein Telescope's vacuum pipe assembly.

Findings

Quantified the impact of particle size and refractive index on scattered light.

Determined maximum particle density limits for the Einstein Telescope.

Proposed cleanliness guidelines for vacuum pipe assembly.

Abstract

High-sensitivity optical measurements such as those performed in interferometric gravitational wave detectors are prone to scattered light noise. To minimize it, optical components must meet tight requirements on surface roughness and bulk defects. Nonetheless, the effectiveness of these measures can be undermined by other sources of scattered light. In this article, we examine scattered light noise caused by particles deposited on surfaces, especially on the baffles inside the vacuum pipes of the Einstein Telescope's interferometer arms. First, we study light scattering by particles deposited on a surface and having diameters from about one tenth to hundred times the light wavelength: we discuss its angular distribution and dependence on particle size and refractive index, and on polarization. Then, we specialize to the case of the Einstein Telescope arms and quantify the maximum allowed density of particles on each arm baffle. We conclude with cleanliness guidelines for the assembly of the vacuum pipes, including the required cleanliness class of the installation environment.