Direct Evidence for Surface Plasmon-Mediated Enhanced Light Transmission through Metallic Nanohole Arrays

Abstract

This paper provides direct evidence for the role of surface plasmons in the enhanced optical transmission of light through metallic nanoscale hole arrays. Near-field optical images directly confirmed the presence of surface plasmons on gold nanohole arrays with interhole spacings larger than the surface plasmon wavelength. A simple interference model provides an intuitive explanation of the two types of fringe wavelengths observed in the near-field optical images. Far-field spectroscopy revealed a surface plasmon band that contributed a factor >8 to the transmission enhancement. Furthermore, silicon nanohole arrays did not exhibit any features in the near-field, which demonstrates that metallic materials are necessary for enhanced light transmission through nanohole arrays.Ground-breaking discoveries in diverse fields such as photonics, 1-5 chemistry, 6,7 and biophysics 8,9 have relied on surface plasmon polaritons (SPPs) to confine and enhance light in the optical near-field. Interest in the fundamental science of SPPs was revived in part by the report of extraordinary light transmission through metallic subwavelength hole arrays 1 which did not follow classical optical theory. 10 SPPs were initially proposed to assist in this enhanced transmission, 11 although subsequent theoretical and experimental work has claimed different mechanisms. [12][13][14] Understanding the role of SPPs in enhanced transmission is crucial for exploiting its nature to beat diffraction in applications such as subwavelength optics and nanophotonics. Here we present direct evidence for SPP-mediated enhanced transmission through gold nanohole arrays by combining, for the first time, near-field and far-field measurements of films with interhole spacings larger than the SPP wavelength. We propose a simple model that explains two types of interference in the near-field patterns and measure an SPP-enhancement factor > 8 in our gold hole arrays.Surface plasmon polaritons are collective charge oscillations that are produced by the resonant interaction between light and free electrons at the interface of metallic and dielectric materials. Additional momentum is required to couple light into SPPs because of their different dispersion relations. 15 This condition is typically satisfied by a corrugated surface such as a grating or by evanescent coupling with a prism or a near-field probe. 15,16 Far-field spectroscopy has been the main approach for investigating enhanced transmission through subwavelength hole arrays; 17,18 however, far-field measurements cannot unambiguously identify the presence of SPPs since their electromagnetic field is trapped in the near-field region of the metal-dielectric interface. Near-field scanning optical microscopy (NSOM) is one technique that can directly image SPPs on a metal surface. In this Letter, we have combined NSOM imaging and far-field spectroscopy on isolated nanoholes and nanohole arrays in gold films to address the question of SPPenhanced optical transmission.Free-standing films of gold perforate...

Tunable plasmonic lattices of silver nanocrystals

“…This field enhancement is responsible for the host of extraordinary optical phenomena exhibited by metal nanostructures, such as resonant light scattering, surface-enhanced Raman scattering 1, 2 , superlensing 3 , and light transmission through optically thick films 4,5 . The shape, size, and periodicity (for arrays) of the metal features explicitly determine the profile and intensity of the observed optical response [5][6][7][8] . However, exploiting the field enhancement offered by plasmonic materials for practical applications is limited by lack of a simple method that can generate these nanostructures with geometric control and regularity.…”

Development of Nanostructured Plasmonic Substrates for Enhanced Optical Biosensing

“…In principle, the peaks of maximum transmission were dependent on the period between the nanoholes. The excitation of surface plasmons seems to mainly contribute to the effect of extraordinary optical transmission, while its interpretation is still underway [73].…”

Periodic surface structures on Ni–Fe film induced by a single femtosecond laser pulse with diffraction rings

“…The transient modulated permittivity lasts for hundreds of fs to picoseconds (ps) [35,36] . At the area with maxima intensity of the diffraction rings, the transient variation of the permittivity is maxima, which works like surface defects and launches SPPs [37][38][39][40] . The interference of the laser field and SPPs modulates the laser field, and further causes a modulated energy deposition.…”

“…Many experimental and theoretical studies indicated that the SPP's excitation would evoke redistribution of the light field on a metal surface, which depended on the light wavelength, permittivity, and surface structures [37][38][39][40] . The interaction between the SPPs and the laser field induces the localization of laser field on the peak and valley of the LDIARs, and further stimulates the LDIARs to split into fine ripples [8,12] .…”

“…There is no diffraction ring that confines the SPP's spreading [38][39][40] , and the ripple widths are nearly equal to the SPP's wavelength [9][10][11][12][13][14][15][16][17][18][19][20] .…”