Letters from Readers
Self-guiding of laser beam has been known for decades
Regarding the article "Self-guiding trick works in solids as well as gases," (January, p. 54), contrary to the statement in the first sentence, self-guiding of a high-power laser beam in air was known in 1966 and given a thorough theoretical treatment in a paper by Keith Brueckner that appeared in AMRAC Proceedings, a classified journal with a highly restricted circulation published by ARPA (now DARPA; "AMRAC" stands for "Anti-Missile Research Advisory Council"). His paper was motivated by the discovery of the carbon dioxide laser in 1965, since that was the first type of laser that promised high output powers, and therefore looked like it might have weapons applications. His paper was the first to consider in detail thermal-blooming and hole-boring phenomena.
Brueckner, with whom I was working at the time, also mentioned in a private conversation that thermal blooming and electrostriction should produce similar guiding effects in dielectrics but I know of no work that was done on that aspect back then. His work remained unknown to workers outside the ABM community for nearly 20 years, but formed the basis for intensive work on the propagation of laser and charged-particle beams through the atmosphere that was far advanced by the early 1980s.
I mention this for your readers' edification, since I doubt that many of them are aware of how long ago it was that the basic ideas of beam self-guidance originated.
Roger P. Main
Roger P. Main Consulting