Kerr nonlinearity effect on femtosecond radiation pulse filamentation in air
N.G. Ivanov1, V.F. Losev1,2
1High Current Electronics Institute of the Siberian Branch of the RAS, 634055, Tomsk, 2/3, Academichesky ave.
2National Research Tomsk Polytechnic University, 30, Lenin Avenue, Tomsk, 634050, Russia
Keywords: керровская нелинейность, филаментация, фокусировка, суперконтинуум, Kerr nonlinearity, filamentation, focusing, supercontinuum
Abstract
The filamentation conditions of a femtosecond laser pulse by its focusing in air are investigated experimentally and theoretically. A good agreement is observed between experimental and calculated data when neglecting the filament plasma. It is shown that at low numerical aperture (NA ≤ 2.15 x 10-3), a Kerr nonlinearity plays a fundamental role in the formation, existence, and termination of a filament. At the initial stage, the Kerr effect leads to the beam self-focusing and emergence of the filament; at the final stage, to radiation defocusing and sharp decrease in its axial intensity due to the beam wave front distortions. In the case of aberration focusing, a spatial quasi-soliton is formed after a visible filament due to the balance between Kerr self-focusing and diffraction extending. The quasisoliton is a source of the directional white supercontinuum.
|
