Strong Modification of the Nonlinear Optical Response of Metallic Subwavelength Hole Arrays

Abstract

The influence of hole shape on the nonlinear optical properties of metallic subwavelength hole arrays is investigated. It is found that the amount of second harmonics generated can be enhanced by changing the hole shape. In part this increase is a direct result of the effect of hole shape on the linear transmission properties. Remarkably, in addition to enhancements that follow directly from the linear properties of the array, we find a hot hole shape. For rectangular holes the effective nonlinear response is enhanced by more than 1 order of magnitude for one particular aspect ratio. This enhancement can be attributed to slow propagation of the fundamental wavelength through the holes which occurs close to the hole cutoff. Metal nanostructures are known to greatly enhance electromagnetic fields in certain geometries. Therefore they can also boost nonlinear optics. Surface-enhanced Raman scattering (SERS) [1], for instance, makes use of nobel metal nanoparticles to amplify the spectroscopic Raman signature of even a single molecule [2]. Sharp nanosize tips [3] provide a more controlled route to enhance the optical field. Another powerful example of nonlinear enhancement is a single circular hole, surrounded by an ordered plasmonic structure [4]. In addition to the use of single structures, ensembles of multiple nanostructures or extended metal objects can also be used to induce nonlinear enhancement randomly positioned metal nanoclusters show nonlinear effects [5]. A popular example of multiple nanostructures acting together is a subwavelength hole array which exhibits extraordinary optical transmission [6] in the linear regime. Calculations indicate that the local field enhancement associated with the transmission through the holes is exceptionally large [7]. Blair and co-workers showed that second-harmonics generation (SHG) on a hole array is possible [8].

Ultrafast optical switching of the THz transmission through metallic subwavelength hole arrays

“…The excitation of surface waves lead to a field enhancement at the metal-dielectric interface and a large transmission through subwavelength apertures at distinct wavelengths associated with the geometrical distance in-between apertures. The highly frequency-dependent transmission, as well as the localized electric-field strengths at the metal interface, means that hole arrays are finding applications in visible spectroscopy, 2 subwavelength optics, 3 nonlinear optics, 4 and photolithography. 5 The recent observation of enhanced transmission of THz ͑Refs.…”

Skirting terahertz waves in a photo-excited nanoslit structure

“…4(c) we show the variation of the FE (at 1. 25 THz, referenced to the unpumped sample) with the optical fluence, obtained by way of two techniques. In the first, the simulated field is directly probed at the center of the slit.…”

“…On the one hand, an electromagnetic wave incident on a resonant sub-wavelength structure can efficiently couple to surface plasmon polaritons (SPP) leading to EOT, 21,22 resulting in high FE in the apertures. [23][24][25][26][27][28] On the other hand, a single infinitely long narrow slit was shown to lead to a significant field enhancement inside the slit leading to broadband EOT. 29,30 A slit etched in a thin metal film can be depicted as a nanocapacitor charged by the light-induced charges on the surrounding metal surface.…”

Coherent control of surface plasmon polariton mediated optical transmission

“…SPPs are electromagnetic excitations confined at the interface between a metal and a dielectric [2]. The ability to create well-defined nanoscale structures in metal films allows engineering of SPP states and has already led to the discovery of several phenomena [3,4], such as the enhancement of fluorescence of single molecules [5], second harmonic generation [6] and the extraordinary optical transmission (EOT) [7,8] of light through subwavelength apertures. However, all these examples rely on static control of the SPP properties, while to realize functional plasmonic circuits, dynamic control is required.…”