Nano-antenna-assisted harmonic generation

Abstract

We report on low-order harmonic generation utilising the plasmonic field enhancement in arrays of rodtype gold optical antennae. Furthermore, we examine their suitability to support high-order harmonic generation (HHG). The low-order harmonics are used as a tool to investigate the nonlinear properties of the antennae. Particular attention is paid to the thermal properties, which become significant at the peak intensities necessary for HHG. A theoretical model explains the experimental findings and enables future improvements. In experiments we observe up to the fifth harmonic order and measure a field enhancement sufficient to support high-order harmonic generation. Moreover, we find a damage threshold for the antennae.

Limitations of Extreme Nonlinear Ultrafast Nanophotonics

“…This was even true for illumination of the bow-ties with light of intensities of ∼ 10 11 W/cm 2 , or a fluence of 0.002 J/cm 2 . Similar observations were made for rod-type antennas in [62]. The delayed destruction of the samples at fluences that are significantly below our determined values for single shot catastrophic LID suggests that a mechanism similar to the one described in [89] might be responsible.…”

“…However, the experimental realization of these conditions ran into trouble. While the spectral features seen in [29] were not perfectly reproduced in any work [38][39][40], some flatly contradicted Kim et al's findings, pin-pointing lines in spectra obtained in such an experiment to 4π incoherent line emission [40]. Meanwhile, Kim's group re-ported follow-up experiments that admittedly showed severe limitations to their previously published results [41].…”

“…In deviation from the presented simulated data, a sapphire wafer was used as the substrate, since this material is beneficial due to its heat conductivity [93], and thus good dissipation of the deposited energy from the metallic structures [29,38,40]. The validity of the earlier simulations might be compromised since the larger refractive index of sapphire (n = 1.76) should have a slight red-shifting effect on plasmonic resonances [94].…”

“…1), as well as successive publications by the same and other groups. Other than the earliest experiment which used bow-tie antennas [29,41], and those relying on the same geometry [39,40], field enhancement for the goal of HHG was explored on single, funnel-shaped devices [41,61], and on linear, rod-type antennas [62]. This concept has inspired theoretical work towards the same goal, such as hypothetically exploring more exotic structures that require demanding production steps.…”

Plasmon-enhanced high-harmonic generation from silicon

“…Harmonics from unpatterned Si behave reversibly. In higher-bandgap materials, the intensity required for high-harmonic generation increases, and extensive damage to the antennas is expected 19,20 . However, generating harmonics from the substrate, rather than from gas atoms placed near the antennas, offers opportunities to overcome the damage limit by encapsulating the antennas in a transparent dielectric medium, such as SiO 2 or MgF 2 .…”