Large-scale self-phase-modulation of picosecond visible pulse under conditions of self-guided propagation in air

Summary form only given. The self-guiding of an intense laser pulse in gaseous media is a result of a balance between two competing nonlinear effects: Kerr effect leading to self-focusing, and defocusing effect of the electron plasma created by the multiphoton ionization. We present a study of the large-scale self-phase-modulation of a moderate-power laser pulse, which exhibits self-guided propagation in air. The picosecond laser pulse [/spl tau/ = 1 ps, /spl lambda/ = 527 nm, second-harmonic of Nd:glass] was slightly focused by an f = +8 m lens in air at atmospheric pressure. With an energy of E = 3.6 mJ, we observed the formation of the single filament of 3 m length which contained almost 50% of the incident pulse energy. The spectral content of the filament was recorded by an OMA III spectrograph.