The plethora of nonlinear optical phenomena can provide an innovative route for developing subwavelength-scale functional optical devices. One of the examples may be the nonlinear mixing of low energy photons (of which the wavelength is a few hundred micrometers) in atomically-thin materials. Here,the experimental proof on the optically-induced nonlinear mixing of terahertz resonances in graphene-integrated metadevices will be presented. Upon ultrafast optical excitation, the conductivity of graphene is reduced for a few picoseconds due to the increase in the Dirac-fermion scattering rate. This fast temporal change of graphene conductivity provides time-varying perturbation to the graphene-integrated metadevices and generates a difference frequency component by the mixing of meta-atoms’ two electric dipole resonances. Ultrafast terahertz spectroscopy corroborates that the characteristic difference-frequency resonance indeed originates from the coupled interaction between graphene and meta-atoms. Further elaborating this concept, it will be shown that the sudden merging of distinct meta-atoms’ resonances by ultrafast optical excitation can also result in frequency conversion.
Bumki Min, "Frequency conversion in optically-excited active metadevices
(Conference Presentation)," Proc. SPIE 9918, Metamaterials, Metadevices, and Metasystems 2016, 99181P (Presented at SPIE Nanoscience + Engineering: August 31, 2016; Published: 9 November 2016); https://doi.org/10.1117/12.2239401.5159519585001.
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