Theodosi Anna, Tsilipakos Odysseas, Soukoulis Costas M, Economou Eleftherios N, Kafesaki Maria
Opt Express. 2022 Jan 3;30(1):460-472. doi: 10.1364/OE.445751.
Graphene is an attractive two-dimensional material for nonlinear applications in the THz regime, since it possesses high third order nonlinearity and the ability to support tightly confined surface plasmons. Here, we study 2D-patterned graphene-patch metasurfaces for efficient third harmonic generation. The efficiency of the nonlinear process is enhanced by spectrally aligning the fundamental and third harmonic frequencies with resonances of the metasurface, leading to spatiotemporal energy confinement in both steps of excitation at ω and radiation at 3ω. This precise resonance alignment is enabled by the 2D-patterning; it is achieved by modifying the dispersion of the underlying plasmons and, thus, the spectral positions of the supported standing wave resonances. Efficiencies as high as -20dB (1%) for input intensity 0.1 MW/cm are achieved. Moreover, we verify that the efficiency does not deteriorate when finite-size metasurfaces are used in place of ideal periodic systems. Our results highlight the potential of graphene-based metasurfaces for nonlinear applications.
石墨烯是一种在太赫兹波段非线性应用中颇具吸引力的二维材料，因为它具有较高的三阶非线性以及支持紧密受限表面等离子体激元的能力。在此，我们研究二维图案化的石墨烯贴片超表面用于高效的三次谐波产生。通过将基频和三次谐波频率与超表面的共振进行光谱对准，非线性过程的效率得以提高，这导致在ω激发和3ω辐射的两个步骤中都实现了时空能量限制。这种精确的共振对准是由二维图案化实现的；它是通过改变底层等离子体激元的色散，进而改变所支持的驻波共振的光谱位置来实现的。对于0.1 MW/cm的输入强度，实现了高达-20dB（1%）的效率。此外，我们验证了当使用有限尺寸的超表面代替理想周期系统时，效率不会降低。我们的结果突出了基于石墨烯的超表面在非线性应用方面的潜力。
