Armin Zach, TOPTICA Projects; Martin Enderlein, TOPTICA Projects; Manuel Brekenfeld, TOPTICA Projects; Dominik Lentrodt, TOPTICA Projects; Leonid Yatsenko, TOPTICA Projects; Sebastian Hepp, TOPTICA Projects; Georg Heinze, TOPTICA Projects; Konstantin Holzner, TOPTICA Projects; Bernhard Ernstberger, TOPTICA Projects; Bernward Dimke, TOPTICA Projects; Philipp Putzer, TOPTICA Projects; Alexander Niggebaum, TOPTICA Projects; Tobias Mayer, TOPTICA Projects; Christopher Renkl, TOPTICA Projects; Frank Lison, TOPTICA Projects; Thomas Tongue, TOPTICA Photonics Inc
https://doi.org/10.64861/BWWF2983
Keywords: sodium, guide star, laser, coherent combining, polychromatic, tip, tilt, daytime operation, FSOC, SDA, SSA, uplink, adaptive optics,
Abstract:
Sodium laser guide star (LGS) systems have become foundational for adaptive optics (AO) in large ground-based telescopes and are emerging as enabling infrastructure for uplink free-space optical communications (FSOC), laser-based space debris tracking, and future debris-maneuvering concepts. As these applications expand beyond classical astronomical use, guide star laser systems must simultaneously deliver higher output power, superior spectral control, long-term operational robustness, and new functionality that addresses fundamental limitations of conventional sodium LGS techniques.
We present a modular, power-scalable sodium guide star laser platform built around a single-frequency 1178 nm distributed-feedback (DFB) seed laser, a narrow-linewidth Raman fiber amplifier (RFA) pumped by a 1120 nm ytterbium (Yb) fiber laser, and second-harmonic generation (SHG) to 589 nm. The standard configuration delivers up to 75 W of single-frequency 589 nm output with a 5 MHz linewidth, ±40 MHz long-term frequency stability, and diffraction-limited beam quality, but higher powers have been demonstrated in the laboratory. Coherent beam combination (CBC) of two Raman-amplified channels at 1178 nm, with a demonstrated combining efficiency exceeding 92%, yields record single-frequency output powers greater than 140 W at 589 nm.
Beyond power scaling, we address the long-standing tip/tilt indeterminacy of sodium LGS by implementing a high-power polychromatic laser guide star (pLGS) based on two-step excitation. A second laser at 569 nm, together with the 589 nm beam, populates a higher-lying sodium energy level whose decay produces return flux at multiple wavelengths, most notably at 330 nm. Density-matrix simulations and sodium vapor cell experiments confirm the two-step excitation scheme. Technology transfer of the RFA and SHG technology from 1178 nm and 589 nm to 1138 nm and 569 nm was demonstrated with high conversion efficiency and stability.
We discuss the implications of this platform for next-generation adaptive optics, high-bandwidth uplink beam correction, and precision laser-based space domain awareness.
Date of Conference: September 15-18, 2026
Track: SDA Systems & Instrumentation