title: Spectral dynamics of THz pulses generated by two-color laser filaments in air: the role of Kerr nonlinearities and pump wavelength.
abstract: We theoretically and numerically study the influence of both instantaneous and Raman-delayed Kerr nonlinearities as well as a long-wavelength pump in the terahertz (THz) emissions produced by two-color femtosecond filaments in air. Although the Raman-delayed nonlinearity induced by air molecules weakens THz generation, four-wave mixing is found to impact the THz spectra accumulated upon propagation via self-, cross-phase modulations and self-steepening. Besides, using the local current theory, we show that the scaling of laser-to-THz conversion efficiency with the fundamental laser wavelength strongly depends on the relative phase between the two colors, the pulse duration and shape, rendering a universal scaling law impossible. Scaling laws in powers of the pump wavelength may only provide a rough estimate of the increase in the THz yield. We confront these results with comprehensive numerical simulations of strongly focused pulses and of filaments propagating over meter-range distances.
authors.forename: A
authors.initials: A
authors.lastname: Nguyen
authors.forename: P
authors.initials: P
authors.lastname: González de Alaiza Martínez
authors.forename: J
authors.initials: J
authors.lastname: Déchard
authors.forename: I
authors.initials: I
authors.lastname: Thiele
authors.forename: I
authors.initials: I
authors.lastname: Babushkin
authors.forename: S
authors.initials: S
authors.lastname: Skupin
authors.forename: L
authors.initials: L
authors.lastname: Bergé