Hiring Institution
Aix Marseille Université (AMU)

PhD-Awarding Institutions
Aix Marseille Université (AMU)
The University of Sydney (USYD)

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Option 1

Local density of States in Complex environments

Spontaneous emission is a random process, somewhat like radioactive decay. Given a set of atoms in an excited state, it is known how long, on average, they stay there before relaxing to the ground state but predicting which atoms relax and which do not is impossible. The spontaneous emission lifetime is a bit like the radioactive half-life, and indeed they differ by only a factor ln(2). For decades it was assumed that the spontaneous emission lifetime was an intrinsic property of the atomic species, a bit like the mass. However, this is not so—the spontaneous emission lifetime depends on the environment in which it is placed. For example, if an atom is placed in a cavity from which light cannot escape then the photons cannot escape and the spontaneously emission is profoundly changed. In fact, the spontaneous emission lifetime is determined by the Local Density of States, the number of states available to photons as a function of position; in the node of the electric field, for example, the Local Density of States vanishes. Measuring these changes is very difficult since atoms are small, and their detailed environments are difficult to control. We have recently pioneered a technique carry out equivalent techniques but, in the microwave, and terahertz regions of the electromagnetic spectrum. Such experiments are relatively easier and make use of techniques that have been developed for these wavelength ranges.

The aim of this project is to carry out microwave and/or terahertz experiments to characterise the Local Density of States in a number of complex environments, for example in near waveguides and in band gaps of photonic crystals and to understand the results using intensive computer simulations. The results will be applied to practical devices, for example scintillators for medical devices or antennas for MRI systems.

Multiwave Imaging (MW) will provide a non-academic secondment and give concrete and valuable insights regarding impact development and creation. MW and Institut Fresnel are already research partners for more than 5 years and have co-supervised several PhD students in various topics including near field energy transfer and biomedical applications. The secondment will also help the PhD student to develop a network of non-academic contacts, expanding their career opportunities.

Option 2

Förster energy transfer

Förster Resonant Energy Transfer (FRET) is a fundamental phenomenon that described the exchange of energy between two atoms (the “donor” and the “acceptor”). Initially one of the atoms is in the excited state and the other is in the ground state. In the final state this situation is reversed. FRET is important in many processes, for example in photosynthesis and to track interactions between proteins. In free space, FRET strongly depends on the relative positions of the donor and the acceptor: if they are far apart the FRET rate, the rate at which the energy transfers, is dominated by radiation and decreases as r-2, but in the near field it drops at r-4 or r-6 depending on the orientation of the dipoles. The FRET rate also depends strongly on the environment, particularly if this environment has features that are comparable to the wavelength. Doing systematic experiments on the FRET rate at optical wavelengths is very difficult because it requires submicrometer positioning in well-controlled environments. We have shown that such experiments can be carried out using microwaves and terahertz radiation.

The aim of this project is to carry out microwave and/or terahertz experiments to characterise the FRET rate a number of complex environments, for example in near waveguides and in band gaps of photonic crystals and to understand the results using intensive computer simulations.

Multiwave Imaging (MW) will provide a non-academic secondment and give concrete and valuable insights regarding impact development and creation. MW and Institut Fresnel are already research partners for more than 5 years and have co-supervised several PhD students in various topics including near field energy transfer and biomedical applications. The secondment will also help the PhD student to develop a network of non-academic contacts, expanding their career opportunities.

Option 3

Investigation of terahertz waveguides by near-field probing

Waveguides, as the name suggests, are devices that guide light. Though the best-known example of these are optical fibres, most waveguide are chip-based and quite short. We recently discovered a method to characterise waveguides using a near-field emitter and receiver. The near-field effects allow for the full control over the excitation of the waveguide modes, which can then be picked up by the receiver. Scanning the receiver and taking the spatial Fourier transform then gives the allowed wavenumbers of the modes as a function of frequency. Although this is conceptually straightforward for simple planar waveguides which, the investigation of much more complicated, and interesting, for waveguides with structure such as photonic crystal waveguides. It will also be possible to investigate more exotic structures in this way, for example those with Weyl points or Dirac points which can occur in topological materials, materials in which the light flow is confined to the edges of a material, rather than to the bulk.

In this project you will carry out experiments to characterise the modes of waveguides and compare with numerical simulations.

Multiwave Imaging (MW) will provide a non-academic secondment and give concrete and valuable insights regarding impact development and creation. MW and Institut Fresnel are already research partners for more than 5 years and have co-supervised several PhD students in various topics including near field energy transfer and biomedical applications. The secondment will also help the PhD student to develop a network of non-academic contacts, expanding their career opportunities.

Stefan Enoch
Martijn de Sterke

Photonics, applied physics, microwave physics, terahertz physics.