等离激元增强的石墨烯光吸收

石墨烯中等离激元具有特殊的光电性质,其和入射光的强烈耦合可以引起光吸收的增强.本文基于时域有限差分法和多体自洽场理论研究了等离激元对处于光学谐振腔中的石墨烯光吸收的影响.由于石墨烯中等离激元与入射光动量和能量不匹配而不能直接相互作用,因此石墨烯上施加了金属光栅结构.研究发现光栅结构能够对入射光进行动量补偿并且能够引起其下石墨烯中的电场强度产生很大程度增强,从而导致在该石墨烯结构中太赫兹等离激元和入射光发生强烈耦合而产生太赫兹等离极化激元,同时引起石墨烯光吸收的增强.希望本文能够加深对石墨烯光电特性的理解以及可以为基于石墨烯的太赫兹光电装置提供一定的理论依据.

Enhanced optical absorption of graphene by plasmon

The plasmons in graphene have the superior properties to metal surface plasmons,such as high field confinement,low Ohmic loss and long wave propagation,highly tunable via electrostatic.More importantly,the frequency of plasmons ranges from terahertz to infrared which indicates that graphene is an ideal candidate for terahertz plamsonics.On the other hand,the strong coupling between incident photons and plasmons in graphene can lead the optical absorption to be enhanced.However,it is difficult for light to couple directly with plasmons in graphene,for the momentum of incident photons cannot match the plasmons in graphene.A metal grating can be used to compensate for the momentum of photons so that it can match that of plasmons in graphene.In this work,we theoretically investigate the effect of plasmons on the terahertz optical absorption of graphene with grating based on finite difference time domain.A great enhancement of electric field component of light field can be obtained near the gold grating strip in the sheet of graphene.Thus,the photons,of which the momentum is compensated for by the grating,can strongly couple with plasmons in graphene.An obviously decrease of the transmission of the graphene structure can be seen at the resonant frequency.The transmission peak corresponds to the resonant frequency spliting into two peaks due to the fact that two plasmon polariton modes are formed by the coupling of photons and palsmons.So we also study the plasmon polariton modes made by coupling photon with palsmon based on the many-body self-consistent method.Two plasmon polariton modes are obtained and an obviously splitting at the resonant frequency can be seen due to the coupling between photons and plasmons.The work conduces to deepening the understanding of the photoelectric properties of graphene and the terahertz plasmonics based on graphene.