Optimal spectral combination of spectrally combined laser beams in the turbulent atmosphere.

The optimal spectral combination of spectrally combined laser beams (SCLBs) propagating from the ground to orbit in the turbulent atmosphere is studied, where the atmospheric effects (e.g., turbulence, extinction and nonlinear self-focusing) are considered. The analytical propagation formulae are derived. It is found that there exists the intensity maximum at the target when the optimal central wavelength λc-opt arrives, and λc-opt is always located around 3.8µm, 8.9µm, or 10.6µm. The λc-opt depends on the spectral width, the initial beam size, and the turbulence strength. Based on λc-opt, the beam quality may be further improved by the method of removing sub-beams with low atmospheric transmittance. However, this method is invalid when the self-focusing is strong enough, while it can significantly improve the beam quality for the large initial beam size.