Preserving High‐Q Lattice Plasmon Resonances for Poor Spatial Coherence of Light: Application in Enhanced Second Harmonic Generation

Abstract

Surface lattice plasmon resonances (SLPR) in periodic arrays of metal nanostructures can feature a narrow spectral linewidth in case of the spectral overlap between the localized plasmons and Rayleigh anomalies. However, because of strong angular dispersion in experimental realizations, the excitation of SLPR requires collimated light, which has high spatial coherence. Here, excellent quality (Q)‐factor preservation in 1D all‐metallic nanograting metasurfaces due to the unique angular dispersion is reported. A high Q‐factor around 400 is obtained even when poor collimation, a numerical aperture (NA) objective with NA = 0.4, is employed for focusing the excitation light. With the advantages of highly focused excitation and high Q‐factor of the SLPR, a strong enhancement of second harmonic generation is realized from the proposed metasurface integrated with a few‐layers of GaSe flake. The results demonstrate that a 1D all‐metallic nanograting metasurface can overcome the demand for collimated light for the SLP resonances and manipulate focused light beams. The avenue of research proposed in this paper can open the door for the use of plasmonic metamaterials with SLPRs in many practical applications involving poorly coherent light sources, like the optoelectronic devices utilizing solar and daylight illuminations.

Plasmonic Metasurfaces with Quality Factors Up to 790 in the Visible Regime

“…[3,4,22] Since the early experimental observations of SLRs in 2008, [23][24][25] of which the Q-factors were found to be only ≈60, continuous efforts have been devoted to improving the Q-factor and great progress has been achieved. [3,22,26] To date, the highest measured Q-factor of SLRs is 330 in the visible [27] or 2340 in the near-infrared regime. [28] However, all these records are achieved by using the in-plane SLRs, which are usually excited under normal incidence.…”