Christian Hafner

Bio: Christian Hafner is an academic researcher from ETH Zurich. The author has contributed to research in topics: Photonic crystal & Plasmon. The author has an hindex of 40, co-authored 231 publications receiving 5662 citations. Previous affiliations of Christian Hafner include École Polytechnique Fédérale de Lausanne.

All-plasmonic Mach–Zehnder modulator enabling optical high-speed communication at the microscale

Abstract: The authors demonstrate a 70 GHz modulator in a 10-μm-long two-dimensionally localized gap-plasmon waveguide system.

Light propagation in a cylindrical waveguide with a complex, metallic, dielectric function.

Abstract: Motivated by problems in scanning near-field optical microscopy, we discuss light propagation in circular dielectric waveguides with finite aluminum cladding. In order to understand the origin of the different solutions, optical modes are first investigated for the dielectric waveguide with infinite aluminum cladding and for the aluminum cylinder. For aluminum a plasma dispersion law is assumed, leading to complex dielectric constants with negative real parts and to generally complex propagation constants. The dependence of the dispersion on the geometry and on the frequency is discussed for the various kinds of modes. We find that the existence of most of the modes is limited to certain frequencies and geometries, i.e., the solutions have a cutoff in the complex propagation constant plane. Contrary to dielectric waveguide theory, where cutoff describes the abrupt transition from propagating to evanescent modes, no other solution is generated when cutoff of a mode is reached. Surface modes and other kinds of modes, such as guided or bulk modes, can either couple between each other or transform into each other.

Negative Refractive Index Materials

Abstract: The main directions of studies of materials with negative index of refraction, also called left-handed or metamaterials, are reviewed. First, the physics of the phenomenon of negative refraction and the history of this scientific branch are outlined. Then recent results of studies of photonic crystals that exhibit negative refraction are discussed. In the third part numerical methods for the simulation of negative index material configurations and of metamaterials that exhibit negative index properties are presented. The advantages and the shortages of existing computer packages are analyzed. Finally, details of the fabrication of different kinds of metamaterials are given. This includes composite metamaterials, photonic crystals, and transmission line metamaterials for different wavelengths namely radio frequencies, microwaves, terahertz, infrared, and visible light. Furthermore, some examples of practical applications of metamaterials are presented.

The generalized multipole technique for computational electromagnetics

Abstract: Geometry, differential and integral forms Coulomb-Ampere theory of electricity and magnetism Maxwell's electrodynamics post-Maxwellian electrodynamics numerical field computations well-known numerical methods Generalized Multipole Technique (GMT) Multiple Multipole Programs (MMP) personal computers and transputers.

Nanoscale roughness on metal surfaces can increase tip-enhanced Raman scattering by an order of magnitude.

Abstract: We studied the influence of nanosteps on signal intensity in gap-mode tip-enhanced Raman spectroscopy (TERS). A benzenethiol monolayer adsorbed on an Au substrate was investigated. The correlation between the TERS signal and the local topography on the substrate shows that a 2 nm high sharp step on the Au surface can significantly increase the enhancement. Furthermore, theoretical models were built, and the numerical simulation results were consistent with our experimental results. The findings provide evidence that nanoscale roughness can play a crucial role in the "hot sites" corresponding to single-molecule surface-enhanced Raman spectroscopy (SERS).

The Optical Properties of Metal Nanoparticles: The Influence of Size, Shape, and Dielectric Environment

Abstract: The optical properties of metal nanoparticles have long been of interest in physical chemistry, starting with Faraday's investigations of colloidal gold in the middle 1800s. More recently, new lithographic techniques as well as improvements to classical wet chemistry methods have made it possible to synthesize noble metal nanoparticles with a wide range of sizes, shapes, and dielectric environments. In this feature article, we describe recent progress in the theory of nanoparticle optical properties, particularly methods for solving Maxwell's equations for light scattering from particles of arbitrary shape in a complex environment. Included is a description of the qualitative features of dipole and quadrupole plasmon resonances for spherical particles; a discussion of analytical and numerical methods for calculating extinction and scattering cross-sections, local fields, and other optical properties for nonspherical particles; and a survey of applications to problems of recent interest involving triangula...

Principles of nano-optics

Abstract: 1. Introduction 2. Theoretical foundations 3. Propagation and focusing of optical fields 4. Spatial resolution and position accuracy 5. Nanoscale optical microscopy 6. Near-field optical probes 7. Probe-sample distance control 8. Light emission and optical interaction in nanoscale environments 9. Quantum emitters 10. Dipole emission near planar interfaces 11. Photonic crystals and resonators 12. Surface plasmons 13. Forces in confined fields 14. Fluctuation-induced phenomena 15. Theoretical methods in nano-optics Appendices Index.

Nanostructured plasmonic sensors.

Abstract: Surface plasmons (SPs) are coherent oscillations of conduction electrons on a metal surface excited by electromagnetic radiation at a metal -dielectric interface. The growing field of research on such light -metal interactions is known as ‘plasmonics’. 1-3 This branch of research has attracted much attention due to its potential applications in miniaturized optical devices, sensors, and photonic circuits as well as in medical diagnostics and therapeutics. 4-8

Nano-optics from sensing to waveguiding

Abstract: The design and realization of metallic nanostructures with tunable plasmon resonances has been greatly advanced by combining a wealth of nanofabrication techniques with advances in computational electromagnetic design. Plasmonics — a rapidly emerging subdiscipline of nanophotonics — is aimed at exploiting both localized and propagating surface plasmons for technologically important applications, specifically in sensing and waveguiding. Here we present a brief overview of this rapidly growing research field.