Fig. 2: Time-domain evolution of harmonic generation.
From: Milliwatt terahertz harmonic generation from topological insulator metamaterials
a Time-domain dynamics (normalized) of a typical fundamental pulse, as measured through electro-optic sampling. b, c Time-domain dynamics (normalized) of generated third-harmonic signal for graphene (b) and Bi2Se3 (c), for four different incident peak field strengths. Both samples are measured in the region with a metal grating for field enhancement. Graphene displays complex dynamics because of the interplay between electronic and phononic heat accumulation and heat-induced (near-)complete THz transparency, which leads to saturation of harmonic generation. Due to the efficient surface-to-bulk dissipation of electronic heat in Bi2Se3, no heat accumulation occurs, and therefore the envelope of the time-domain signal basically follows that of the incident, fundamental waveform. d, e Schematic illustration of heat accumulation in graphene (d) and efficient surface-to-bulk dissipation in the TI (e)
