Beam Combining and Atmospheric Propagation of High Power Lasers
Interim rept. May-Sep 2011
NAVAL RESEARCH LAB WASHINGTON DC BEAM PHYSICS BRANCH
Pagination or Media Count:
Solid state lasers are one of the candidates for efficient and compact directed energy systems. To achieve the necessary power levels many laser beams must be combined to form a single focused beam. We discuss coherent and incoherent combining of multi-kW, high quality lasers and the effects of atmospheric turbulence and aerosols on the propagation of the combined beams. We analyze the beam centroid wander and spreading contributions to the spot size and obtain the power on target for a range of turbulence levels. We find that there is virtually no difference in the power on target between coherently combined and incoherently combined beams. We also find that for km-range propagation in moderate turbulence, there is a maximum intensity that can be propagated to the target which is independent of initial beam size and beam quality. In addition, due to turbulence, it is not necessary to have extremely high quality beams, i.e., M2 3 is sufficient. For low levels of turbulence, tip-tilt corrections can be used to reduce the beam centroid wander contribution to the spot size. The HELCAP laser propagation code is used to compare the propagation efficiency of coherently and incoherently combined beams for various levels of turbulence and propagation ranges.
- Lasers and Masers