The Extremely Large Telescope Interferometer

TL;DR

The ELTI concept proposes using advanced SPAD imaging sensors and the ELT's large aperture to enable visible-light intensity interferometry with unprecedented angular resolution, opening new frontiers in high-resolution optical astronomy.

Contribution

This paper introduces a novel interferometry approach combining segmented sub-pupil beam combination, megapixel SPAD arrays, and high-dispersion spectroscopy for the ELT, enabling new observational capabilities.

Findings

Enables milliarcsecond imaging of stellar surfaces

Probes extreme-gravity environments around compact objects

Potential detection of Earth-sized exoplanets

Abstract

The ELTI concept capitalizes on recent breakthroughs in large-format SPAD (Single-Photon Avalanche Diode) imaging sensors, combining them with the unprecedented collecting area and segmented architecture of the ELT to deliver a fundamentally new observational capability for the 2040s: visible-light intensity interferometry with ELT-scale angular resolution and quantum-limited temporal sampling. By uniting three transformative innovations - segmented sub-pupil beam combination, megapixel SPAD arrays with picosecond time resolution, and high-dispersion spectroscopy - ELTI opens an entirely new region of observational parameter space in angular resolution, spectral bandwidth, and temporal precision. This capability enables true milliarcsecond imaging of stellar surfaces, direct probes of extreme-gravity and strong electromagnetic-field environments around compact objects, precision studies of accretion physics, and even the potential detection of Earth-sized exoplanets through minute visibility modulations. ELTI thus positions the ELT as the world-leading facility for ultra-high-resolution optical astronomy in the coming decades.