Development of a plasma waveguide for high-intensity laser pulses

Abstract

We present a comprehensive report on recent experiments [Durfee and Milchberg, Phys. Rev. Lett. 71, 2409 (1993); Durfee, Lynch, and Milchberg, Opt. Lett. 19, 1937 (1994)] in which the channeling of intense laser pulses over distances much greater than a Rayleigh length was demonstrated using a two-laser-pulse technique. The first pulse creates a breakdown spark in a gas target, and the expansion of the resulting hot plasma forms a channel which guides a second pulse, injected into the channel after an appropriate delay. Data are presented for channels of 24 Rayleigh lengths (0.7 cm), while pulses have been channeled up to 70 Rayleigh lengths (2.2 cm), with up to 75% of the energy in the injected pulse focal spot coupled into the guide. In spite of the high intensities of the channeled beam (here up to ${10}^{14}$ W/${\mathrm{cm}}^2$), the propagation is linear and should remain so at even higher intensities. Single-mode, multimode, and leaky mode propagation of the channeled beam is observed, with the mode structure depending on the delay and the gas density. Along with these experimental results, we present a model of the laser-gas interaction and the resulting plasma hydrodynamics and calculate beam propagation and mode structure in plasma waveguides. A special property of a plasma waveguide is that the mode structure is wavelength independent, resulting in a wavelength-independent guiding condition.