Abstract
Black phosphorus surface plasmon (BPSP) is a new promising candidate material for electromagnetic field confinement at the subwavelength scale. Here, we theoretically investigated the light confinement, second-order nonlinearity and lifetimes of tunable surface plasmons in nanostructured black phosphorus nanoflakes with superstrates. The grating structure can enhance the local optical field of the fundamental wave (FW) and second harmonic wave (SHW) due to the surface plasmon resonance. Based on the coupled mode theory (CMT), a theoretical model for the nanostructured black phosphorus was established to study the spectrum features of FW. The lifetimes of the plasmonic resonant modes were investigated with the finite difference time domain (FDTD) simulations and CMT. Since the permittivity of black phosphorus depends on its Fermi energy and electron scattering rate, the lifetimes of plasmonic absorption modes are tunable with both the Fermi energy and scattering rate. The intensity, wavelengths and spectral width of BPSP resonance modes and their lifetimes can be precisely controlled with the Fermi energy, scattering rate, side length and refractive index of the superstrate. The sensitivity is described by varying the refractive index of the superstrate such as an aqueous solution. We have introduced a second-order nonlinear source to investigate the SHW of nanostructured black phosphorus. This paper presents the corner/edge energy distribution and the tunable lifetime of BPSP as well as their unprecedented capability of photon manipulation for second-order nonlinearity within the deep subwavelength scale. The configuration and method are useful for research of the absorption, lifetime of light and nonlinear optical processes in black phosphorus-based optoelectronic devices, especially the modulation and sensing applications.
Highlights
Black phosphorus surface plasmon (BPSP) is a new promising candidate material for electromagnetic field confinement at the subwavelength scale
The lifetimes of plasmonic absorption modes are tunable with the Fermi energy, the scattering rate, side length of black phosphorus and refractive index of the superstrate
With the introduction of the second-order nonlinear source, we investigate the second-order nonlinearity such as second harmonic generation (SHG), sum frequency generation (SFG) and difference frequency generation (DFG)
Summary
Paper mental wave and second harmonic wave has been observed in metallic structures and nanostructured metal or graphene. Experiments and theories have shown that linear transmission through arrays is sensitive to many factors such as array periodicity, hole shape and size, incidence angle, and film thickness. Methods of enhancing the SHG were widely studied by double plasmonic resonance, Fano resonance, and even nanocup structure.31 They measured the SHG from a periodic array using femtosecond laser pulses and observed the SHG signal intensity. We numerically analyze the confined surface plasmon of the fundamental wave and the second harmonic wave in the nanostructured black phosphorus nanoflake, which forms a grating to enhance the light–matter interaction. The linear absorption spectra for various Fermi energies, the electron scattering rate, side length of black phosphorus and the refractive indexes of superstrates with the FDTD method agree well with the theoretical description. The lifetimes of plasmonic absorption modes are tunable with the Fermi energy, the scattering rate, side length of black phosphorus and refractive index of the superstrate. The methods are useful for investigating the lifetime of light and nonlinear optical processes in black phosphorus-based optoelectronic devices, especially the black phosphorus modulation and sensing applications.
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