Ultrafast dynamics and surface plasmon properties of Silicon upon irradiation with mid-infrared femtosecond laser pulses

Abstract

We present a theoretical investigation of the yet unexplored ultrafast processes and dynamics of the produced excited carriers upon irradiation of Silicon with femtosecond pulsed lasers in the mid-infrared (mid-IR) spectral region. The evolution of the carrier density and thermal response of the electron-hole and lattice subsystems are analysed for various wavelengths λL in the range between 2.2 μm and 3.3 μm where the influence of two and three-photon absorption mechanisms is explored. The role of induced Kerr effect is highlighted and it manifests a more pronounced influence at smaller wavelengths in the mid-IR range. Elaboration on the conditions that leads to surface plasmon (SP) excitation indicate the formation of weakly bound SP waves on the material surface. The lifetime of the excited SP is shown to rise upon increasing wavelength yielding a larger than the one predicted for higher laser frequencies. Calculation of damage thresholds for various pulse durations τp show that they rise according to a power law (~τ_p^{ζ(λ_L) ) where the increasing rate is determined by the exponent ζ(λ_L). Investigation of the multi-photon absorption rates and impact ionization contribution at different τp manifests a lower damage for λL=2.5 μm compared to that for λL=2.2 μm for long τp.

arXiv commentarXiv admin note: text overlap with arXiv:1807.11422

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• Ionisation processes and laser induced periodic surface structures in dielectrics with mid-infrared femtosecond laser pulses
• Modelling ultrafast non-equilibrium carrier dynamics and relaxation processes upon irradiation of hexagonal Silicon-Carbide with femtosecond laser pulses
• Tailoring surface topographies on solids with Mid-IR femtosecond laser pulses
• Ionization dynamics and damage conditions for transparent materials irradiated with Mid-Infrared femtosecond pulses
• Ultrafast laser welding of silicon