Unveiling the Origin of Third Harmonic Generation in Hybrid ITO–Plasmonic Crystals

Abstract

The advent of novel lithographic techniques enabling the shaping of noble metals at the nanoscale is offering unprecedented opportunities for generating and manipulating light within subwavelength regions [1][2][3] . In recent years, the development of functional nanoscale elements such as plasmonic antennas, transducers between free radiation and localized energy [4,5] , has led to major advances in various research fields including single molecule detection [6][7][8] , directive nanosources of light [9][10][11] , vibrational spectroscopy [12][13][14] and nonlinear interactions at the nanoscale [15][16][17] . For the latter, while the enhanced local fields created by plasmonic structures can be exploited for upconverting light at the nanoscale and for ultrafast processing of optical signals [18][19] , their opacity prevents exploiting phase matching in order to reach high nonlinear emission, which severely limits their practical use. Therefore, the development of nanoscale devices exhibiting stronger nonlinear responses is highly required for proposing future efficient integrated nanophotonic components.One promising strategy for reaching higher nonlinear nanoscale responses is related to the integration of an active nonlinear medium in the near field of a plasmonic structure. Indeed, while most works in nonlinear nanophotonics have focused on intrinsic responses from pure

Third-harmonic generation in optical nanoantennas: efficiency enhancement

“…The linear and nonlinear responses simulated at the same time in which the nonlinear investigations started by measuring the THG spectra from the hybrid and bare plasmonic nanoantenna. By having an excitation at frequency ω, the third-order susceptibility (3)  of the material induces a nonlinear polarization (3) (3 ) P  defined by [11]:…”

“…Optical nanoantennas have been recently proposed to enhance the efficiency of nonlinear optical processes such as THG which is mainly related to modifying the linear optical properties and the resonance lifetime of the plasmonic antennas [10,11]. The confined plasmonic resonances can be identified from peaks in scattering and absorption cross-sections and nearfield radiation patterns [10].…”

“…The confined plasmonic resonances can be identified from peaks in scattering and absorption cross-sections and nearfield radiation patterns [10]. This is utilized to build optical nonlinearities at the nanoscale, without any dependency of phase-matching conditions [11]. Resonances of metallic nanoparticles like gold and silver usually take place at UV-visible wavelengths.…”

Investigating the origin of third harmonic generation from diabolo optical antennas

“…Recently, the origin of THG enhancement is mainly distinguished via the shift of harmonic spectra by hybrid dipole nanoantennas. [20][21][22] In this letter, by investigating the dependence of the harmonic intensity on the polarization of the laser, we demonstrate another method to determine the origin of the THG by dipole nanoantennas. Instead of positioning a dielectric crystal into the feedgap, here we insert a thin Au nanorod to electrically connect the adjacent bowtie nanoantenna tips, which is referred to as the interconnector hereafter.…”