From : "...Optics.org News"
Dayton OH March 11,2014 – The US Defense Advanced Research Projects Agency (DARPA) says that a developmental laser weapon has precisely hit a target from 7 kilometres, thanks in large part to a 21-element optical phased array (OPA) that maintains good beam quality over such large stand-off distances. Although the latest demonstration was not with the kind of high-power beam that would ultimately be needed for such weapons - a ramp to 100 kilowatt is envisaged over the next three years - it does show that optics are able to compensate for the distortion caused by atmospheric turbulence, a key technical challenge for laser weapons.
Joe Mangano, the program manager within DARPA's "Excalibur" project, says that the recent demo shows that the OPA-corrected laser can outperform conventional systems that suffer from reduced beam quality. Maintaining a good beam shape is critical to ensure that sufficiently concentrated power is delivered to a target to destroy it. The 21-element OPA used by DARPA, which was made by Ohio-based Optonicus, comprised three identical clusters of seven fiber lasers. Each cluster measures 10 cm across.Combined with an "ultra-fast" algorithm, the OPA is said to be able to correct for atmospheric turbulence within a millisecond.