Characteristics of Local Electric Field Excitation in the Asymmetric Nanostructure Illuminated by Ultrafast Laser Pulse

Boyu Ji Department of Physics, Changchun University of Science and Technology, Changchun, China Zuoqiang Hao Department of Physics, Changchun University of Science and Technology, Changchun, China Jingquan Lin Department of Physics, Changchun University of Science and Technology, Changchun, China

Localized surface plasmon resonances has been widely used in the field of chemosensing，surface enhanced Raman scattering, biomedicine and near-field control[[1]]. Nanoscale symmetric structure is an ideal for obtaining local surface plasmon resonance while illuminated with ultrafast linear polarization laser pulse. In many applications, especially for the cases of illumination source are white light, or femtosecond laser that has a wide spectral bandwidth, a significant drawback of the symmetric geometric nanostructure is their narrowband response, the narrow structure with dual or multiple bands are desirable for a number of promising applications[2]. Adoption of the asymmetric nanostructure can result in multiple resonant peaks and greatly enhance the spectral absorption, which may find applications in such as selective optical fibers, multiple detector array. In this paper, to the best of our knowledge, systematical research of excitation and dynamic response of the plamon resonance of asymmetric structure under ultrafast laser excitation will be firstly presented. Extinction spectrum, local electric field intensity, current density distribution and temporal response of the local electric field for the asymmetric nanocross are simulated using FDTD method. It is found that, in addition to arms that are parallel with the laser polarization occur strong local plasmonic resonance, perpendicular arms (vertical to laser polarization) can get large local electric field enhancement as symmetry of the nanocross is broken. For the asymmetric nanocross extinction spectra show red-shift as arm length increases and simultaneous multiple resonant wavelength peaks appear. Current density distribution of the nanocross further supports the result of the local electric field enhancement. Temporal response of electric field in arms of the asymmetric nanocross shows that the parallel arms start to oscillation under the ultrafast laser illumination, followed by oscillation of local electric field of the perpendicular arms. Underneath physics of the perpendicular arm excitation is given. The results obtained in this paper are important to the field that using plasmon effect as perfect absorber and also to the field of optical near-field coherent control.

 

  1. F. J. Rodriguez-Fortuno, M. Martínez-Marco, B. Tomas-Navarro, et al., Applied Physics Letters 98(13), 133118-133118-3 (2011)
  2. J. Homola, Chemical reviews, 2008, 108(2): 462-493

        

linjingquan@cust.edu.cn

 

 









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