# A Proposed Method for a Photon-Counting Laser Coherence Detection System to Complement Optical SETI

## TL;DR

This paper proposes a photon-counting laser coherence detection system to improve the sensitivity of optical SETI searches, capable of distinguishing laser signals from natural emissions using coherence properties.

## Contribution

It introduces a novel coherence-based detection method employing photon-sensitive detectors and an asymmetric interferometer, enhancing sensitivity over traditional spectroscopic techniques.

## Key findings

- Detection sensitivity exceeds current methods for continuous laser sources
- Threshold sensitivity of less than 1 photon per second per square meter
- Effective against background spectral bandwidth of 0.1 nm

## Abstract

The detection of laser radiation originating from space is a positive indicator of Extra Terrestrial Intelligence (ETI). Thus far the optical search for ETI (OSETI) has looked for enhanced brightness in the form of either narrow-band spectral emission or time correlated photons from laser pulses. In this paper it is proposed to look for coherence properties of incoming light in a manner that can distinguish against atomic emission lines. The use of photon sensitive detectors and a modulating asymmetric interferometer has been modelled. The results suggest that the sensitivity of detection for continuous laser sources would be better than current spectroscopic approaches, with detection thresholds of $<$1 photon s$^{-1}$m$^{-2}$ against a background with a spectral bandwidth of 0.1nm over an observation time of 750s.