Abstract

Very high peak power and ultrashort pulse duration result in various nonlinear effects when fs-TW laser pulses propagate through air. In addition to linear diffraction, self-focusing as well as local plasma-induced defocusing has to be taken into account. Self-guided filaments can take place when a dynamic balance between the above mechanism is established. Such filaments remain confined for distances much longer than the Rayleigh length, reaching several tens of meters under well chosen circumstances. The spatial confinement in the filaments provides a long interaction path, which enhances the nonlinear frequency conversion processes by self phase modulation, stimulated Raman scattering and four-wave-mixing. The spectral content of the filaments observed in a 2-TW laser beam propagating in atmospheric-pressure rare gases has been investigated in the visible and the UV ranges [1]. A so-called hypercontinuum has been measured from 150 nm to 900 nm.

© 2000 IEEE