On 9 December 2018, the research group headed by Professor Yongsheng Zhao from Institute of Chemistry, Chinese Academy of Sciences has constructed hybrid plasmonic structures based on the 3D spiral WSe2 for achieving highly efficient second-order nonlinear parametric processes below the diffraction limit. The research article entitled “Hybrid Three-Dimensional Spiral WSe2 Plasmonic Structures for Highly Efficient Second-Order Nonlinear Parametric Processes” has been published in Research (Research 2018, Article ID: 4164029 DOI: 10.1155/2018/4164029). https://spj.sciencemag.org/research/2018/4164029/.
Broadband tunable coherent light sources with small footprint and low power consumption have attracted great attention because of their potential applications ranging from high-throughput sensing to on-chip photonic communication. Second harmonic generation (SHG) and sum frequency generation (SFG), which are based on the second-order nonlinear optical parametric processes (which utilizes nonlinear dielectric materials as media to convert electromagnetic wave of frequency ω1 and ω2 into a new wave with the frequency ω3), are emerging as ideal alternatives to nanoscale lasers due to their wide wavelength modulation range. Transition metal dichalcogenides, with broken inversion symmetry structure in the monolayer limit which brings about nonvanishing second-order nonlinear susceptibility, have been widely applied for obtaining SHG at nanoscale size. Unfortunately, the atomic thickness of TMDC leads to weak light-matter interaction owing to the nearly 1 nm interaction length. Meanwhile, due to the diffraction limit of light, the small sizes (at subwavelength scale) of TMDC lead to poor field confinement, which results in low nonlinear optical conversion efficiency. Thus, thicker TMDC nanostructures with effective subwavelength electromagnetic field confinement are needed for highly efficient nonlinear optical applications.
Recently，The research group headed by Professor Yong Sheng Zhao from Institute of Chemistry, Chinese Academy of Sciences has constructed hybrid plasmonic structures based on the 3D spiral WSe2 (Fig. a) for achieving highly efficient second-order nonlinear parametric processes below the diffraction limit. Owing to the AA lattice stacking structure (Fig. b), the second-order nonlinear polarization of the adjacent layers would have the same orientation under the linearly polarized laser excitation. This would lead to the constructive interference between them, which is conducive for efficient SH radiation. In addition, compared with the atomic thickness of monolayer WSe2, the 3Dspiral WSe2 flakes with the increase of thickness have much longer light-matter interaction length, which is beneficial for the enhancement of light-matter interaction and thus the enhanced SHG. Moreover, the 3D spiral WSe2 structures were transferred onto the top of a smooth silver film with a 10-nanometer magnesium fluoride (MgF2) insulating gap to construct hybrid 3D spiral WSe2 plasmonic structures for further enhancing the light-matter interaction (Fig. c). As a result, extremely high external SHG conversion efficiency is achieved (Fig d, e). Meanwhile, the SHG and SFG are realized simultaneously when the hybrid 3D spiral TMDC plasmonic structures were excited by two separated fundamental waves (980 nm and 1064 nm laser) (Fig. f).
Figure. (a, b) Schematic illustration of a spiral WSe2 structure (a) and the corresponding basal planes stacking (AA stacking) order (b); (c) Schematic illustration of a hybrid spiralWSe2 plasmonic structure where a singleWSe2 sits on top of the MgF2 layer near the Ag film; (d) Spatial resolved spectra collected from the hybrid spiralWSe2 structure shown in the inset. Inset: SH image of a single hybrid spiralWSe2 structure excited with a CW laser (1064 nm); (e) Spectra of SHG and FW from hybrid spiralWSe2 plasmonic structure excited with 1064 nm CW laser; (f) The spectrum collected from the hybrid spiral WSe2 plasmonic structure excited with 1064 nm and 980 nm CW laser simultaneously.
The enhanced light-matter interaction and extremely high nonlinear optical conversion efficiency below the diffraction limit would lay the foundation for the construction of typical devices with specific functions based on the nonlinear optical processes. Such as, optical switches, optical logical gates and optical transistors.
Tag: Emerging materials research