Jean-Michel Benoit

High density InAlAs/GaAlAs quantum dots for non-linear optics in microcavities

Structural and optical properties of InAlAs/GaAlAs quantum dots grown by molecular beam epitaxy are studied using transmission electron microscopy and temperature- and time-resolved photoluminescence. The control of the recombination lifetime (50 ps-1.25 ns) and of the dot density (5.10–8-2.1011 cm–3) strongly suggest that these material systems can find wide applications in opto-electronic devices as focusing non-linear dispersive materials as well as fast saturable absorbers.

High quality factor confined Tamm modes

We demonstrate that quality factors up to 5000 can be obtained in Tamm-like hybrid metal/semiconductor structures. To do this, a Bragg mirror is covered by a thin transparent layer and a metallic film. The reduced losses of these modes are related to an intermediate behavior between conventional Tamm plasmon and Bragg modes lying deeper in the semiconductor medium. One of the most striking features of this approach is that these super Tamm modes can still be spatially confined with the metal. Confinement on micrometric scale is experimentally demonstrated. The simplicity and versatility of high-Q mode control by metal structuration open perspectives for lasing and polaritonic applications.

From localized to delocalized plasmonic modes, first observation of superradiant scattering in disordered semicontinous metal films

Our study proposes a new way to observe and explain the presence of extended plasmonic modes in disordered semi-continuous metal films before the percolation threshold. Attenuated total reflection spectroscopy allows us to follow the transition of plasmon modes from localized to delocalized resonances, but also reveals unobserved collective plasmon modes. These bright modes with out-of-plane polarization are transverse collective plasmonic resonances. By increasing the density of metallic nanoparticles in a wavelength scale, we observe an angular squeezing and spectral broadening of these modes. This behavior can be explained considering that transverse localized surface plasmon resonances of each nanoparticle, all resonant, interact in a collective and coherent way via a common confined light mode: the evanescent wave. These many-body resonances, which have never been clearly identified in such disordered semi-continuous metal films, can be described by analogy with atomic physics as superradiant modes. Our first simulations, using dyadic Greens formalism, demonstrate the existence of this mode for a dense array of plasmonic systems. In this regime, the radiation rate of the superradiant mode increases with the number of tied dipoles. This explains the spectral broadening observed in our work and constitutes the first manifestation of superradiance mode in plasmonic random structure.

Coherence in disordered emitters coupled to surface and long-range plasmons

Localized and delocalized plasmons in metallic nanostructures are associated with a strongly confined electromagnetic field, inducing an enhanced interaction with emitters located in the close environment of the metal. When the plasmon/emitter interaction overtakes the damping in the system, the system enters into strong coupling regime leading to light-matter hybridization [1]. This strong coupling has been observed with a large number of materials, in particular disordered materials which are constituted by a collection of independent emitters (molecules, semiconductor quantum dots...). The spatial and dynamic properties of an assembly of molecules in strong coupling are drastically modified compared to the same molecules in weak coupling [2]. We will present our on-going research on strong coupling between plasmons and molecular emitters. If we take into account the microscopic structure of the molecular film, collective effects between the delocalized plasmon and the set of molecules occurs. The excitations are not localized in a single emitter anymore but delocalized on a large number of molecules due to the formation of an extended hybridized state over several microns which modifies various properties of molecular materials like conductivity or reactivity [3]. However, the extension of the coherent state is limited by the reduced plasmon propagation length, due to metal losses. We will show that the coherence length can be extended using a low loss surface plasmon in a symmetrical structure leading to Long Range Surface Plasmon (LRSP) [4, 5] (Fig. 1a). Simulations using a transfer matrix method are performed to optimize the parameters of the LRSP formation and its interaction with the aggregated dye and compared to experiments. After the demonstration of strong coupling between aggregated dyes and long range plasmon (Fig. 1b), we will evaluate the extension of the coherent polaritonic mode in the structures. A coherence length up to several tens of microns can be achieved. The parameters of these modes will be discussed to optimize the interaction with the organic material.

High Density InAlAs/GaAlAs Quantum Dots as an Efficient Enhanced Kerr Material for Transverse Non-linear Optics in Microcavities

InAlAs/GaAlAs quantum dots are studied using transmission electron microscopy, photoluminescence. This systems appear as promising materials for laser and non-linear optics in the visible/near infrared range, particularly as a focusing Kerr-like medium for pattern formation.