Ultrashort, ultraintense laser pulses undergo competing interactions: The nonlinear Kerr effect self-focuses the beam, while multiphoton ionization generates a plasma that defocuses the beam and prevents it from collapsing. The result is a self-channeled, nondiffracting beam with a tight core, termed a filament, consisting of the intense laser field and the generated plasma (see Physics Today, August 2001, page 17). Filaments are self-healing and emit broadband light in the forward direction, properties that yield a variety of applications, including remote atmospheric sensing and spectroscopy. Recent work by Pavel Polynkin (University of Arizona), Demetrios Christodoulides (University of Central Florida), and colleagues has put a new twist on the filaments. Unlike earlier studies, which relied on Gaussian or other axially symmetric beam profiles, Polynkin and company used axially asymmetric beams: With a phase modulator, they shaped the transverse profile of their femtosecond pulses into the form of a two-dimensional Airy...

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