A resonance phenomenon in the zeroth diffraction order of a gold-wire grating is explained by the excitation of surface polaritons. This effect is connected with a strong enhancement of the electromagnetic fields on the wire surface and consequently with a peak of power losses in the grating material. Measurements of the zeroth-order transmittance have been performed on gold gratings with periods of 1 and 2 micrometers in the near-infrared region which are in agreement with theoretical results. Furthermore, dispersion relations of the first-order coupling mode are presented having large energy gaps in the center of the Brillouin zone. It is shown that this energy gap strongly depends on the wire profile. In this coupling branch, however, practically no dispersion could be observed for optical wavelengths less than the grating period.

We present a theoretical approach for calculating the fields diffracted by gratings made of highlyconducting wires that have a rectangular shape. The fields between the wires are represented in terms of modal expansions that satisfy the approximated impedance boundary condition. Our results show thatthis procedure is particularly suited to dealing with gold gratings used in the infrared range, a spectral region where the assumption of a perfect conductor does not hold, and where the rigorous modal method assuming penetrable wires exhibits numerical instabilities linked with the high conductivity of gold. Numerical results are presented, and the theory is used to determine wire parameters by fitting theoretical and experimental data.

Gratings with periods smaller than visible wavelengths in ambient white light will exhibit enhanced colors if the profile is designed so that resonant light interaction occurs in the visible range. Resonances have a frequency-selective influence to the grating diffraction inducing colors in transmittance and reflectance, respectively. Apart from the well-known surface-plasmon polariton excitations and cavity resonances, newly discovered resonances in TE-polarization can be exploited for colorizing wire-gratings, when simply illuminated by unpolarized white light. Colors can be laterally tuned by varying the grating profile. The capability of generating images by sub-wavelength gratings is exemplified by a metallic wire grating embedded in a plastic foil with a lateral variable modulation depth. This method for producing colored images is predestined for industrial mass production and will have ever more practical applications such as for security features.

Plasmonic biosensors, particularly arrays of nanoholes on thin gold films, have been widely explored in recent years as possible platforms for fast medical diagnostic. In this work, we present a screening method for leukemia cancer markers that uses a plasmonic biosensor based on nanohole arrays fabricated on plastic substrates. The low-cost, scalable, and reproducible nanohole array structures were fabricated by UV nanoimprinting technique. The relative concentration of human immunoglobulin kappa and lambda light chains in blood serum was employed as a screening method. The kappa/lambda concentration ratio was used to determine an unbalance in the immunoglobulin production due to leukemia. The platform was tested using serum samples from patients with known leukemia diagnoses. The results indicated that this inexpensive and flexible plasmonic platform is a promising tool for routine screening in clinical settings.

Electromagnetic resonances on metallic slit gratings induced by TM polarized incident light have been investigated and physically interpreted. We have developed an electromagnetic model imposing surface impedance boundary conditions on the metallic grating surface from which we derive simple formulas explaining all physical properties of these resonances. It is demonstrated that Fabry-Perot (or cavity) resonances are generated by the zeroth slit mode yielding extraordinary transmission. For very narrow slits, the resonant H-field is squeezed to the slit walls and causes enhanced power losses. The excitation of surface plasmon polaritons (SPPs), however, is generated by two mode coupling. SPPs are linked to sharp absorption peaks and dips in transmittance. It is shown that these phenomena are primarily caused by the interaction of the electromagnetic fields with the finite conducting slit walls. These findings have been confirmed by measured transmittance data of gold gratings with periods of 0.5 μm, 1 μm, and 2 μm.