Excitation Of Surface Plasmon Polariton Modes Research Articles

Two-dimensional high-quality Ag/Py magnetoplasmonic crystals

We demonstrate a perspective approach for the fabrication of functional high-quality magnetoplasmonic crystals based on a 2D periodical perforated silver film covered by a thin layer of ferromagnetic metal (Permalloy). The wavelength-angular spectra of the 2D crystals reveal a large number of high-quality resonant features associated with the excitation of surface plasmon-polariton modes of various orders. Due to the presence of a ferromagnetic material on both plasmonic interfaces, pronounced magnetic effects are observed for all excitations and are influenced by the coupling between various modes. The suggested magnetoplasmonic crystal composition with high-quality resonant optical and magneto-optical properties gives perspective for the control over the light propagation as well as for sensor applications.

Multispectral plasmonic supercells

By excitation of surface plasmon-polariton modes upon a multi-periodic metallic surface, we presented a new class of semiconductor-based multiband plasmonic supercell with potential application in trapping the light over a wide range of wavelengths and angles of incidence. The concept for three encoded periods corresponding to different spatial frequencies of surface modulation function at a silver:germanium interface shows a plasmon-enhanced absorption probability of 18.13% in a wide wavelength band of 400–1200 nm. This translates to an enhanced absorption factor of 7.5% in the Ge photoactive layer for a multiband structure compared to that of a single-band.

Plasmon polariton enhanced mid-infrared photodetectors based on Ge quantum dots in Si

Quantum dot based infrared (IR) photodetectors (QDIPs) have the potential to provide meaningful advances to the next generation of imaging systems due to their sensitivity to normal incidence radiation, large optical gain, low dark currents, and high operating temperature. SiGe-based QDIPs are of particular interest as they are compatible with silicon integration technology but suffer from the low absorption coefficient and hence small photoresponse in the mid-wavelength IR region. Here, we report on the plasmonic enhanced Ge/Si QDIPs with tailorable wavelength optical response and polarization selectivity. Ge/Si heterostructures with self-assembled Ge quantum dots are monolithically integrated with periodic two-dimensional arrays of subwavelength holes (2DHAs) perforated in gold films to convert the incident electromagnetic IR radiation into the surface plasmon polariton (SPP) waves. The resonant responsivity of the plasmonic detector at a wavelength of 5.4 μm shows an enhancement of up to thirty times over a narrow spectral bandwidth (FWHM = 0.3 μm), demonstrating the potentiality of this approach for the realization of high-performance Ge/Si QDIPs that require high spectral resolution. The possibility of the polarization-sensitive detection in Ge/Si QDIPs enhanced with a stretched-lattice 2DHA is reported. The excitation of SPP modes and the near-field components are investigated with the three-dimensional finite-element frequency-domain method. The role that plasmonic electric field plays in QDIP enhancement is discussed.

Modes Manipulation Within Subwavelength Metallic Gratings

Surface plasmon polariton (SPP) and cavity modes supported by the plasmonic gratings are often of hybrid nature in ruling light-nanostructure interactions. The coupling of incident light to SPP waves through the excitation of SPP modes usually traps the light at the air-metal interface, while the coupling to standing waves through cavity modes confines the light within the cavities. However, in a specific application, the highly selective coupling of incident light to either SPP or cavity mode is always required. We present here, for a single metal-insulator-metal (MIM) groove, the coupling strength of incident light to a certain mode can be engineered by varying the groove width and depth. To further enhance the coupling selectivity, the periodicity was introduced to the MIM grooves: When the period approaches (deviates from) the wavelength of SPPs, the incident light highly couples to SPP (cavity) mode, due to the constructive (destructive) interference between the propagating SPPs at metal-air interfaces. Two types of metallic gratings, aluminum grating with its period approaching the λSPP and iridium grating with its period far away deviating from the λSPP, were fabricated and measured. The almost null TM transmission through aluminum grating and detection of surface enhanced Raman scattering (SERS) signal from iridium grating solidly guarantee the validity of the proposed method in manipulating the modes, through which the energy flow can be guided to its supposed-to-appear regions.

Second harmonic generation in metamaterials based on homogeneous centrosymmetric nanowires

We present a comprehensive theoretical study of the second harmonic generation (SHG) in metamaterials consisting of arbitrary distributions of cylindrical nanowires made of centrosymmetric materials. The electromagnetic field at both the fundamental frequency (FF) and second harmonic (SH), as well as the total cross section, the absorption cross section, and the scattering cross section, are calculated by means of a numerical algorithm based on the multiple scattering method. Our algorithm fully describes the nonlinear optical response of the metamaterial by incorporating the contributions of both the surface and bulk nonlinear polarizations and can be applied to both s- and p-polarized incident waves. We use this numerical method to investigate the SHG in a series of particular cases of practical interest, namely, a single metallic cylinder, chains of metallic cylinders, and periodic and random distributions of such cylinders. In particular, we study the relation between the local field enhancement, via the excitation of surface plasmon-polariton modes, and the amount of energy absorbed or scattered in the far-field, at the FF and the SH.

Surface-enhanced raman scattering from molecules adsorbed on GaAs surfaces

We present the observation of surface-enhanced Raman scattering (SERS) from vibrations of molecules adsorbed on a GaAs surface. We used two different SERS activation procedures. One consists of evaporating a silver island film on the semiconductor surface and the other is based on the use of a chemical etching process. The observed SERS spectra of the adsorbed molecules are similar with both SERS activation procedures. We could not detect Raman scattering from surfaces with either the deposited Ag film or the etching procedure because the vibrational spectra of molecules adsorbed on semiconductor surfaces were too weak to be detectable. With both methods there is enhanced Raman scattering from the surface of the semiconductor due to the excitation of surface-plasmon polariton modes introduced by the surface roughness. These results prove that adsorbed species on semiconductor surfaces can be detected by SERS spectroscopy. This is important for the extension of the applicability of Raman spectroscopy, and suggests the possibility of utilizing the SERS effect as a new surface probe of semiconductor surfaces.