Ultra-broadband enhancement of nonlinear optical processes from randomly patterned super absorbing metasurfaces

Abstract

Broadband light trapping and field localization is highly desired in enhanced light-matter interaction, especially in harmonic generations. However, due to the limited resonant bandwidth, most periodic plasmonic nanostructures cannot cover both fundamental excitation wavelength and harmonic generation wavelength simultaneously. Therefore, most previously reported plasmonic nonlinear optical processes are low in conversion efficiency. Here, we report a strong enhancement of second harmonic generation based on a three-layered super absorbing metasurface structure consisting of a dielectric spacer layer sandwiched by an array of random metallic nanoantennas and a metal ground plate. Intriguingly, the strong light trapping band (e.g. >80%) was realized throughout the entire visible to near-infrared spectral regime (i.e., from 435 nm to 1100 nm), enabling plasmonically enhanced surface harmonic generation and frequency mixing across a broad range of excitation wavelengths, which cannot be achieved with narrow band periodic plasmonic structures. By introducing hybrid random antenna arrays with small metallic nanoparticles and ultra-thin nonlinear optical films (e.g. TiO2) into the nanogaps, the nonlinear optical process can be further enhanced. This broadband light-trapping metastructure shows its potential as a building block for emerging nonlinear optical meta-atoms.

Superabsorbing Metasurfaces with Hybrid Ag–Au Nanostructures for Surface‐Enhanced Raman Spectroscopy Sensing of Drugs and Chemicals

“…This is due to the nanocavity‐induced absorption enhancement with engineered optical constants, as we reported in refs. . By changing the shapes of randomly distributed NPs deposited under different conditions, the effective optical constants of surface nanoparticle layer can be tuned to control the bandwidth and amplitude of the absorption of the three‐layered nanocavity structure.…”

“…Based on this experimental characterization, one can see that after the second‐step fabrication process, the metasurface structure still preserves the broadband light trapping feature with slightly shifted resonant wavelengths. These smaller gaps are promising to obtain stronger localized field, which is highly desired for enhanced light–matter interaction (e.g., SERS and surface‐enhanced nonlinear optics), as will be discussed below.…”

Superhydrophobic 3D‐Assembled Metallic Nanoparticles for Trace Chemical Enrichment in SERS Sensing

“…Although hot spots are highly desired for enhanced light‐matter interaction (e.g., SERS and surface‐enhanced nonlinear optics [ 18 ] ), a major challenge is how to introduce the analytes into the nanovolumes to interact with the boosted localized field. [ 11 ] To overcome this challenge, realizing a superhydrophobic surface is an effective strategy to concentrate and localize analytes at a specific position.…”

Semiconductor Thin Film Based Metasurfaces and Metamaterials for Photovoltaic and Photoelectrochemical Water Splitting Applications

“…For a periodic pattern of nanoplasmonic units, this enhancement has a narrow spectral coverage and this is not desired for photoconversion applications. However, in the random nanopatterns (such as colloidal assemblies or dewetted particles) with multiple gap distances, this light confinement can be achieved in a broad wavelength range . Hence, in such designs, the incident power will be efficiently coupled into the semiconductor layer rather than being lost in metal.…”