Quantum Multiphysics Modeling of Metallic Surfaces and Nanostructures under Femtosecond Laser Illumination

Femtosecond lasers can strongly interact with metallic surfaces and nanostructures leading to surface processing and hot electron generation. Recently, we theoretically studied (L. Khosravi Khorashad and C. Argyropoulos, “Unraveling the temperature dynamics and hot electron generation in tunable gap-plasmon metasurface absorbers,” Nanophotonics, vol. 11, issue 17, pp. 4037-4052, Apr. 2022) the non-equilibrium dynamics of hot electron relaxation processes in metallic (plasmonic) metasurface absorbers when excited by femtosecond lasers. Strong light–matter interactions combined with quantum effects at the nanoscale are dominant in these nano configurations. A quantum hydrodynamic nonlocal model approach was employed to accurately predict the induced electric field distribution confined in the ultrathin dielectric nanogap. The utilized hydrodynamic model considered electron-electron repulsion which resulted in quantum electron pressure in the system. This approach led to a more accurate calculation of the induced electric field in the dielectric spacer nanogap considering the electric field spillage into the metallic sections of the metasurface. Additionally, we calculated the hot electron generation rate (non-thermalized electrons) using a formula based on the quantum dynamics of equation of motion and the density matrix theory. We utilized the two-temperature model (TTM) coupled with the nonlocal model for the first time to compute the time dependent electron and lattice temperature ultrafast non-equilibrium dynamics. The TTM allowed us to demonstrate temperature dynamics of hot electrons and their transition into thermal carriers at various laser illumination timescales from femto to nano seconds. We further demonstrated the resulted tunable ultrafast transient absorption response as a function of wavelength and time which can be useful in the emerging field of time-variant nanophotonics.