Second harmonic generation spectroscopy on hybrid plasmonic/dielectric nanoantennas

• Published in: Light, science & applications Vol. 5; no. 1; p. e16013
• Main Authors: Linnenbank, Heiko, Grynko, Yevgen, Förstner, Jens, Linden, Stefan
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01-01-2016; Springer Nature B.V; Nature Publishing Group
• Subjects: 639/624/399/1015; 639/624/399/354; 639/624/400/1021; 639/624/400/385; Antennas; Applied and Technical Physics; Atomic; Classical and Continuum Physics; Dielectrics; Gold; Harmonic analysis; Harmonics; Lasers; Molecular; Nanoparticles; Nanoscience; Nanostructure; Nonlinearity; Optical and Plasma Physics; Optical Devices; Optics; Original; original-article; Photonics; Physics; Physics and Astronomy; Plasmonics; Spectroscopy; Spectrum analysis; nanoantennas; plasmonics; second harmonic generation
• ISSN: 2047-7538; 2095-5545; 2047-7538
• DOI: 10.1038/lsa.2016.13

Plasmonic nanoantennas provide unprecedented opportunities to concentrate light fields in subwavelength-sized volumes. By placing a nonlinear dielectric nanoparticle in such a hot spot, one can hope to take advantage of both the field enhancement provided by nanoantennas and the large, nonlinear optical susceptibility of dielectric nanoparticles. To test this concept, we combine gold gap nanoantennas with second-order, nonlinear zinc sulfide nanoparticles, and perform second harmonic generation (SHG) spectroscopy on the combined hybrid dielectric/plasmonic nanoantennas as well as on the individual constituents. We find that SHG from the bare gold nanoantennas, even though it should be forbidden due to symmetry reasons, is several orders of magnitude larger than that of the bare zinc sulfide nanoparticles. Even stronger second harmonic signals are generated by the hybrid dielectric/plasmonic nanoantennas. Control experiments with nanoantennas containing linear lanthanum fluoride nanoparticles reveal; however, that the increased SHG efficiency of the hybrid dielectric/plasmonic nanoantennas does not depend on the nonlinear optical susceptibility of the dielectric nanoparticles but is an effect of the modification of the dielectric environment. The combination of a hybrid dielectric/plasmonic nanoantenna, which is only resonant for the incoming pump light field, with a second nanoantenna, which is resonant for the generated second harmonic light, allows for a further increase in the efficiency of SHG. As the second nanoantenna mediates the coupling of the second harmonic light to the far field, this double-resonant approach also provides us with control over the polarization of the generated light.
Plasmonic nanoantennas: second harmonic generation in gold nanoantennas and dielectric nanoparticles
Enhanced second harmonic generation (SHG) is studied in hybrid systems consisting of plasmonic nanoantennas and dielectric nanoparticles. Such systems could potentially exploit the field enhancement of the nanoantennas and the high nonlinear susceptibility of the dielectric nanoparticles. Heiko Linnenbank and co-workers in Germany tested this concept by performing linear extinction and SHG spectroscopy measurements on gold gap nanoantennas and nonlinear zinc sulphide nanoparticles or lanthanum fluoride nanoparticles for which second-order processes were nominally forbidden due to symmetry. They found that SHG was highly sensitive to changes in the nanoparticles’ environment but independent of the nonlinear properties of the nanoparticles. By using two nanoantennas – one resonant for the pump field and the other resonant for the SHG light – the researchers were able to achieve a high SHG conversion efficiency.