Filamentation of ultrashort pulse laser beams resulting from their propagation over long distances in air

Abstract

The propagation of high-power short-pulse laser beams over considerable distances in air is studied both experimentally and via numerical simulations. Filaments are formed after 5–10 m and their propagation over distances in excess of 200 m is reported for the first time. The lateral dimensions of the filaments are found to range from about 100 μm to a few millimeters in diameter. The early values of plasma electron density have been inferred to be a few times 1016 cm−3 using longitudinal spectral interferometry. For 500 fs pulses and a wavelength of 1053 nm, the energy in the filament can be quite high initially (∼8 mJ) and is found to stabilize at about 1.5–2 mJ, after about 35 m. A simple model based on the nonlinear Schrödinger equation coupled to a multiphoton ionization law appears to describe several experimental results quite well.

Optimal laser-pulse energy partitioning for air ionization

“…An interplay between focusing by the Kerr effect and defocusing effects including ionization and the saturation of the Kerr effect [18,19] ensures intensities in the range of several tens of TW/cm 2 over long distances [20,21].…”

Femtosecond Filamentation in Air

“…Several groups gave persistent reports on multifilamentary structures propagating over several hundreds of meters [9,29,64,92]. The formation of filaments at kilometric distances in the sky was also reported from the detection of the supercontinuum by a telescope [70,89].…”

“…Yang et al [92] measured the phase contrast and obtained similar results. Several groups announced the presence of filaments with a millimeter size after a propagation over several tens of meters [9,29,56]. In these filaments, the intensity of the pulse is lower than the ionization threshold, but the optical Kerr effect still plays its role.…”

“…For ultrashort pulses, multiphoton absorption therefore occurs in steps of small amount of energy. This explains the propagation over long distances of an intense fs laser pulse, To summarize, the most spectacular properties of light filaments are: a) Their propagation over long distances from the meter scale in the laboratory to the kilometric scale outdoor [29,52,54,70].…”

Laser femtoseconde, filamentation, nuage et orage

“…Certes, les filaments peuvent se propager sur de longues distances [10], et leur formation aété détectéeà une distance de 2 km [11]. Cependant, hormis les limitations issues de la durée de vie du plasma (quelques microsecondes pour les ions O -2 [12]), une question pertinente concerne la possibilité de produire de longs filaments continûment ionisés, non pas dans une atmosphère claire, mais sous l'orage : les nuages comme la pluie constituent alors un obstacle majeurà la propagation du laser.…”