Investigation of Surface Electromagnetic Waves with Multi-Heterodyne Scanning Near-Field Optical Microscopy

Tristan Sfez
2010
Thèse EPFL

In this thesis, we present the development of a tunable Multi-Heterodyne Scanning Near-Field Optical Microscope (MH-SNOM). This instrument has been built and evaluated for the investigation of optical near fields in amplitude, phase and polarization. With this microscope, the response of a structure illuminated with two orthogonally polarized beams can be simultaneously measured both in amplitude and phase. Moreover, the integral state of polarization at the surface of a specimen can be retrieved under specific conditions. We demonstrate the capabilities of the system through a series of measurements involving Surface Electromagnetic Waves (SEWs). We have mainly focused our attention on a particular class of SEWs known as Bloch Surface Waves (BSWs). The propagation of BSWs on the outer surface of a silicon nitride multilayer has been studied in detail. Furthermore, we show that this propagation is affected by the presence of shallow dielectric corrugations such as a subwavelength grating or at the straight interface with a coated portion of the multilayer. In particular, we demonstrate that ultra-thin (thickness < λ/10) dielectric ridges may act as BSW waveguides. Combining the detection capabilities of the MH-SNOM with a numerical treatment of the experimental data, we are able to separate the transverse and longitudinal field components of the three modes propagating within a specific BSW waveguide. This new structure provides interesting opportunities in waveguide-based biosensing schemes in which the ridge is realized with functionalized molecular layers of nanometric thickness. Finally, we investigate a structure sustaining another type of SEW: Surface Plasmon Polaritons (SPPs). This structure is designed for the asymmetrical coupling of SPPs at normal incidence. Through a detailed analysis of the spatial spectra, we show that, in addition to SPPs, the field contains other near-field components. All these experiments demonstrate the expected MH-SNOM capabilities of measuring the amplitude, phase and polarization of optical near fields. The MH-SNOM therefore serves as a powerful tool for the investigation with subwavelength resolution of optical near fields generated in structures such as integrated optics, photonic crystals, cavities, resonators, etc.

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Tristan Sfez
2010
Thèse EPFL

Résumé

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https://infoscience.epfl.ch/record/146687?ln=fr

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Concepts associés (3)

Bloch's theorem

In condensed matter physics, Bloch's theorem states that solutions to the Schrödinger equation in a periodic potential can be expressed as plane waves modulated by periodic functions. The theorem is named after the physicist Felix Bloch, who discovered the theorem in 1929. Mathematically, they are written where is position, is the wave function, is a periodic function with the same periodicity as the crystal, the wave vector is the crystal momentum vector, is Euler's number, and is the imaginary unit.

Cristal photonique

Les cristaux photoniques sont des structures périodiques de matériaux diélectriques, semi-conducteurs ou métallo-diélectriques modifiant la propagation des ondes électromagnétiques de la même manière qu'un potentiel périodique dans un cristal semi-conducteur affecte le déplacement des électrons en créant des bandes d'énergie autorisées et interdites. Les longueurs d'onde pouvant se propager dans le cristal se nomment des modes dont la représentation énergie-vecteur d'onde forme des bandes.

Optique

L'optique est la branche de la physique qui traite de la lumière, de son comportement et de ses propriétés, du rayonnement électromagnétique à la vision en passant par les systèmes utilisant ou émettant de la lumière. Du fait de ses propriétés ondulatoires, le domaine de la lumière peut couvrir le lointain UV jusqu'au lointain IR en passant par les longueurs d'onde visibles. Ces propriétés recouvrent alors le domaine des ondes radio, micro-ondes, des rayons X et des radiations électromagnétiques.