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.

References in corpus (6)

• Ultrashort filaments of light in weakly-ionized, optically-transparent media
• Measurement of the nonlinear refractive index of air constituents at mid-infrared wavelengths
• Boosting terahertz generation in laser-field ionized gases using a sawtooth wave shape
• Generalized Miller Formulae
• Theory of terahertz emission from femtosecond-laser-induced micro-plasmas
• Sensitivity of propagation and energy deposition in femtosecond filamentation to the nonlinear refractive index

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• Enhancing terahertz generation from a two-color plasma using optical parametric amplifier waste light
• High order Brunel harmonics and supercontinuum formed by a weak optical pump in presence of a strong terahertz field
• Air-photonics terahertz platform with versatile micro-controller based interface and data acquisition