Lunar Laser Ranging with High-Power CW Lasers

TL;DR

This paper introduces a high-power continuous-wave laser technique for lunar laser ranging, significantly enhancing measurement precision and enabling advanced lunar and planetary studies.

Contribution

It develops a detailed link budget and noise analysis for CW laser LLR, demonstrating potential for millimeter to sub-0.1 mm accuracy with next-generation retroreflectors.

Findings

Achieves sustained millimeter-level ranging with high-power CW lasers.

Mitigates common-mode errors through differential measurements.

Enables sub-0.1 mm precision with atmospheric turbulence averaging.

Abstract

We present a high-power continuous-wave (CW) lunar laser ranging (LLR) technique that has the potential to significantly improve Earth--Moon distance measurements. Using a 1 kW CW laser at 1064 nm and a 1 m-aperture telescope as an example, we develop a detailed link budget and analyze the prevailing noise sources to assess system performance when ranging to next-generation ~10 cm corner-cube retroreflectors (CCRs). Unlike legacy arrays, these smaller CCRs are designed to yield lower intrinsic range errors, yet their reduced reflective area results in lower photon return rates, posing challenges for pulsed LLR systems. The photon-rich CW approach, by providing continuous high-power illumination, overcomes this limitation, reducing shot noise and enabling sustained millimeter-level ranging with a pathway to sub-0.1 mm precision. Furthermore, by alternating measurements between widely separated lunar reflectors, differential LLR mitigates common-mode station errors to achieve tens-of-micrometer precision, limited primarily by uncorrelated atmospheric turbulence. This scalable approach -- integrating high-power CW lasers, narrowband filtering, and rapid atmospheric turbulence averaging -- enables next-generation gravitational tests, precision lunar geodesy, and improved lunar reference frames in support of planetary exploration.