Laser guide star return-flux gain from frequency chirping

ABSTRACT Spectral hole burning reduces sodium laser guide star efficiency. Due to photon recoil, atoms that are initially resonant with the single-frequency get Doppler shifted out of resonance, which return flux. Frequency-chirped (also known as frequency-swept) continuous-wave lasers have potential mitigate effect spectral and even increase efficiency beyond theoretical limit a laser. We investigate flux frequency-chirped stars its dependence on environmental chirping parameters. On-sky measurements frequency-chirped, performed at Roque de los Muchachos Observatory La Palma. A fast photon-counting receiver system is employed resolve return-flux response during frequency sweeps gaining insights into population dynamics layer. At launched power 16.5 W, we find maximum gain in 22 per cent compared fixed-frequency amplitude order 150 MHz rate 0.8 µs−1. Time-resolved period confirm our understanding These first enhancement for excited by single-frequency-chirped For higher powers, effectiveness expected increase, could be highly beneficial telescopes equipped high-power adaptive optics systems.