Dramatic enhancement of supercontinuum generation in elliptically-polarized laser filaments

TL;DR

This paper demonstrates that elliptical polarization states can dramatically enhance supercontinuum generation in laser filaments, with the effect driven by the medium's delayed rotational response, offering new control over broadband laser sources.

Contribution

It reveals that specific elliptical polarizations induce anomalous spectral broadening in filamentation, linked to the medium's rotational response, providing a novel method to control supercontinuum generation.

Findings

Spectral broadening is enhanced for certain elliptical polarizations.

The phenomenon is linked to the medium's delayed rotational response.

Filament length and polarization state are modified by elliptical polarization.

Abstract

Broadband laser sources based on supercontinuum generation by femtosecond laser filamentation have enabled applications from stand-off sensing and spectroscopy to the generation and self-compression of high-energy few-cycle pulses. Filamentation relies on the dynamic balance between self-focusing and plasma defocusing, mediated by the Kerr nonlinearity and multiphoton ionization respectively. The filament properties, including the supercontinuum generation, are therefore highly sensitive to the properties of both the laser source and the propagation medium. Here, we report the anomalous spectral broadening of the supercontinuum for filamentation in molecular gases, which is observed for specific elliptical polarization states of the input laser pulse. The resulting spectrum is accompanied by a modification of the supercontinuum polarization state and a lengthening of the filament plasma column. Numerical simulations confirm that the anomalous behavior originates from the delayed rotational response of the medium, demonstrating a new parameter to control supercontinuum generation.