title: The effect of standing acoustic waves on the formation of laser-induced air plasmas.
abstract: The expected location of an air plasma produced by a focused YAG laser pulse has been found to be influenced by the acoustics of the surrounding environment. In open air, the expected location of a laser-induced air plasma is centered close to the focal point of the lens focusing the laser beam. When confining the same beam coaxially along the interior of a quartz tube, the expected location of the air plasma shifts away from the focal point, toward the focusing lens, in a region of less laser fluence. This shift is caused by an interaction between standing acoustic waves (formed from sound waves produced by previous laser-induced plasmas) and the impinging laser pulse. Standing acoustic waves in a tube produce areas (antinodes) of slightly higher and slightly lower pressure than ambient atmospheric conditions, that in turn have a noticeable affect on the probability of creating an air plasma at a given location. This leads to two observed phenomena: Increased probability of air plasma formation before the optical focal point is reached, and the formation of distinct (separate) air plasmas at the antinodes themselves.
authors: College of the Holy Cross, Worcester, MA 01610, USA.
authors: Stephanie M
authors: SM
authors: Craig
authors: Kara
authors: K
authors: Brownell
authors: Brendon
authors: B
authors: O'Leary
authors: Christopher
authors: C
authors: Malfitano
authors: Jude A
authors: JA
authors: Kelley