Ultrafast excitation of nonequilibrium carriers under intense pulses offers unique opportunities for controlling the optical properties of semiconductor materials. In this work, we propose a scheme for ultrafast generation of surface plasmon-polaritons (SPPs) via a transient metagrating formed under two interfering optical pump pulses in a thin film of the semiconductor $\mathrm{Ga}\mathrm{As}$. The grating is formed due to modulation of the refractive index associated with the nonequilibrium carrier generation. The temporal grating structure formed enables the generation of SPP waves at the $\mathrm{Ga}\mathrm{As}$/$\mathrm{Ag}$ interface via weak probe pulse excitation. We propose a theoretical model describing nonequilibrium carriers formation and diffusion and their contribution to permittivity modulation via Drude and band-filling mechanisms. We predict that by tuning the parameters of the pump and probe, one can reach the critical coupling regime and achieve efficient generation of SPPs on timescales of 0.1–1 ps.

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• Carrier dynamics
• Photonics
• Plasmonics
• Surface plasmon polariton
• Ultrafast optics
• III-V semiconductors
• Metasurfaces
• Ultrafast pump-probe spectroscopy