Dramatic enhancement of supercontinuum generation in\n elliptically-polarized laser filaments

Broadband laser sources based on supercontinuum generation by femtosecond\nlaser filamentation have enabled applications from stand-off sensing and\nspectroscopy to the generation and self-compression of high-energy few-cycle\npulses. Filamentation relies on the dynamic balance between self-focusing and\nplasma defocusing, mediated by the Kerr nonlinearity and multiphoton ionization\nrespectively. The filament properties, including the supercontinuum generation,\nare therefore highly sensitive to the properties of both the laser source and\nthe propagation medium. Here, we report the anomalous spectral broadening of\nthe supercontinuum for filamentation in molecular gases, which is observed for\nspecific elliptical polarization states of the input laser pulse. The resulting\nspectrum is accompanied by a modification of the supercontinuum polarization\nstate and a lengthening of the filament plasma column. Numerical simulations\nconfirm that the anomalous behavior originates from the delayed rotational\nresponse of the medium, demonstrating a new parameter to control supercontinuum\ngeneration.\n