Researchers report broadband tip-enhanced nonlinear optical response in a plasmonic nanocavity

Squeezing gentle past the diffraction restrict and controlling the optical processes brought on by nano-confined gentle are central problems with nanophotonics. Particularly, localized and enhanced gentle on the plasmonic nanogaps in scanning probe microscopes supplies us with a singular platform for acquiring site-specific optical info on the molecular/atomic scale.

Very just lately, not solely linear but additionally nonlinear optics have been utilized to such tip-enhanced nanoscopy to realize increased sensitivity and spatial decision. On this context, understanding the intrinsic nonlinear optical properties of plasmonic nanocavities is of rising significance in controlling nanosized nonlinear optics extra exactly.

Researchers led by Toshiki Sugimoto, Affiliate Professor on the Institute for Molecular Science, succeeded in elucidating the intrinsic nonlinear optical properties of tip-substrate plasmonic nanocavities. Combining a wavelength-tunable femtosecond pulse laser system with a scanning tunneling microscope and specializing in the tip-enhancement of second harmonic era (SHG), they reported an unexpectedly broad tip-enhanced nonlinear optical response in a plasmonic nanocavity (see determine 1).

They demonstrated that the tip-enhancement of SHG is maintained over the seen to infrared wavelength vary (see determine 2a–c). Furthermore, the distinguished geometrical results of plasmonic suggestions dominating this broadband enhancement capability have been additionally verified; the broadband nonlinear optical property of tip-substrate nanocavities is considerably influenced not solely by the buildings of nanosized tip apexes but additionally by micrometer dimension tip shafts (see determine second–i).

The origin of those geometrical results was unveiled by exact numerical simulations of plasmonic fields inside tip-substrate nanocavities. They theoretically demonstrated that broadband tip-enhanced SHG properties will be considerably altered in response to nanometer- and micrometer-scale tip buildings. The simulations incorporating this structural info excellently seize the experimentally noticed habits (see determine 2j–l).

Extra detailed evaluation of those simulated outcomes revealed the origin of geometrical results on tip-enhanced SHG; whereas the micrometer-scale tip shafts prolong the spectral vary of the sphere enhancement to the near- and mid-infrared areas, the nanometer-scale tip apexes primarily contribute to boosting seen/near-infrared gentle. This means that the micrometer-scale tip shafts and nanometer-scale tip apexes collectively allow the simultaneous enhancement of each mid/near-infrared excitation and visual/near-infrared radiation processes, respectively, realizing the strongly enhanced SHG over the seen to infrared broadband area.

This demonstration of the numerous broadband enhancement capability of plasmonic nanogaps supplies a brand new foundation for intentional management of site-specific nonlinear optical phenomena which can be essentially accompanied by drastic wavelength conversion. Furthermore, the group’s findings pave the way in which for creating next-generation tip-enhanced nanoscopy by exploiting varied nonlinear optical processes.

Primarily based on these new strategies, correlated chemical and topographic info can be efficiently addressed with final spatiotemporal decision, selling cutting-edge microscopic analysis in a wide range of bodily, chemical and organic processes occurring in heterogeneous environments.