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.