Why metallic surfaces with grooves a few nanometers deep and wide may strongly absorb visible light.

It is theoretically shown that nanometric silver lamellar gratings present very strong visible light absorption inside the grooves, leading to electric field enhancement of several orders of magnitude. It is due to the excitation of quasistatic surface plasmon polaritons with particular small penetration depth in the metal. This may explain the abnormal optical absorption observed a long time ago on almost flat Ag films. Surface enhanced Raman scattering in rough metallic films could also be due to the excitation of such quasistatic plasmon polaritons in grain boundaries or notches of the films.

Generation and control of hot spots on commensurate metallic gratings.

We study the light localization on commensurate arrangements of deep metallic sub-wavelength grooves. We theoretically show that as the degree of commensuration tends to an irrational number new light localization states are produced. These have properties close to that reported for hot spots on disordered surfaces and are not permitted for simple period gratings. Existence of these new resonances is experimentally provided in the infra-red region by reflectivity measurements performed on two commensurate samples with respectively two and three slits per period. Manipulations of these hot spots which can be controlled from far-field could be used for high sensitivity spectroscopy applications.

Controlling strong electromagnetic fields at subwavelength scales.

We investigate the optical response of two subwavelength grooves on a metallic screen, separated by a subwavelength distance. We show that the cavity, Fabry-Perot-like mode, already observed in one-dimensional periodic gratings and known for a single slit, splits into two resonances in our system: a symmetric mode with a small Q factor, and an antisymmetric one which leads to a much stronger field enhancement. This behavior results from the near-field coupling of the grooves. Moreover, the use of a second incident wave allows control of the localization of the photons in the groove of our choice, depending on the phase difference between the two incident waves. The system acts exactly as a subwavelength optical switch operated from far field.

Photonic crystal sensor based on surface waves for thin-film characterization.

A new sensor based on optical surface waves in truncated one-dimensional photonic crystals is proposed for use in determining the optical properties of metallic or dielectric thin films and bulk media. Specifically, the method of optical characterization takes into account the changes that the surface waves of a layered structure undergo when either a thin film of arbitrary material is added at the surface or the optical properties of transmission medium change. For the surface-wave excitation the Kretschmann configuration used in attenuated total reflectance is employed.

Precision in the ellipsometric determination of the optical constants of very thin films.

The possibilities of obtaining the optical constants of very thin films from ellipsometric measurements are analyzed with the help of the approximate Drude formulas. The influence of ellipsometric errors on the determination of the optical constants of thin films is examined. It is shown that the accuracy is extremely small when the dielectric constant epsilon of the thin film is equal to the refractive index of the substrate [equation].