Recent progress in sodium beacon development

Researchers at the Starfire Optical Range have been researching laser beacons for AO for nearly 30 years. We developed four different sodium-wavelength lasers, all of which were based on diode-pumped, sum-frequency Nd:YAG oscillators. In 2016, we combined light from two commercial, 22 W, sodium-wavelength lasers to form a single beacon. These lasers, which use resonant-frequency doubling of light from a Raman fiber-amplifier, were built by MPB Communications and Toptica Photonics, under a contract from the European Southern Observatory. In 2019, we started to develop and procure a 75 W sodium-wavelength laser to enable better correction of turbulence in poor seeing. In conjunction with ESO, we have also started work to increase the return flux from sodium beacons by shifting or chirping the laser wavelength to compensate for recoil of optically pumped sodium atoms. Initial tests have demonstrated that chirping can increase beacon brightness by 10–20 percent.