Ultrafast excitation and current-induced amplification of terahertz plasma waves in bilayer two-dimensional electron gases

Plasma wave generation in two-dimensional electron gases (2DEGs) offers a promising platform for studying collective electron dynamics and developing coherent terahertz (THz) radiation sources. This work proposes a new scheme for generating THz plasma waves by combining ultrafast optical excitation with current-driven instability in a coupled bilayer 2DEG system. We show that an obliquely incident femtosecond laser pulse can effectively seed broad-spectrum plasma waves, which are subsequently amplified via the two-stream instability arising from the relative motion between the two electron layers. Specifically, a self-consistent hydrodynamic model is employed to derive the dispersion relation, and particle-in-cell simulations are performed to characterize the wave growth. The results show good agreement between the dispersion theory and simulations. The mode with the highest theoretical growth rate dominates the output spectrum, confirming the instability-driven amplification. The influences of laser and 2DEG parameters on the spectrum are also analyzed. This study provides fundamental insights into plasma instabilities in coupled low-dimensional systems and offers a viable pathway toward tunable on-chip THz sources.