Understanding the physics of coherent LiDAR

TL;DR

This paper explains the fundamental physics of coherent LiDAR, highlighting its advantages, detection sensitivity, and factors affecting signal strength, with rigorous derivations from first principles.

Contribution

It provides a detailed theoretical analysis of coherent LiDAR physics, including photon detection sensitivity and collection efficiency, which enhances understanding of its performance.

Findings

Photon detection sensitivity depends on the number of photons needed for robust detection.

Signal strength is highly dependent on laser beam focusing quality.

Coherent LiDAR offers immunity to ambient light and precise velocity measurements.

Abstract

Coherent LiDAR (Light Detecting And Ranging) is a promising 3D imaging technology that provides significant advantages over more traditional LiDAR systems. In addition to being immune to ambient light, it directly measures the velocity of moving objects by sensing Doppler shift of light, and can achieve exceptional depth accuracies. The goal of this manuscript is to explain the basic physics of coherent LiDAR with rigorous derivations from first principles. We first discuss the sensitivity of coherent detection, and derive the number of photons needed to robustly detect a LiDAR return. We then turn our attention to the collection efficiency of coherent LiDAR, and show that signal strength is strongly dependent upon how well the laser beams are focused.