Thesis--Munich. / In Periodical Room.

University, Diss., 2005--Bremen.

Les polaritons de cavité sont des quasi-particules, partiellement matière-t partiellement lumière, crées lors du couplage fort d'un exciton et d’un photon de cavité. A une certaine température et densité de particules, les polaritons de cavité peuvent subir une transition de phase de type quasi-Bose-Einstein et condenser dans l'état de plus basse énergie du système; dans ces conditions, la cavité émet de la lumière cohérente et le dispositif associé est appelé laser à polaritons. ZnO est l'un des matériaux les plus adaptés pour la fabrication des lasers à polaritons fonctionnant à température ambiante, en raison de ses excellentes propriétés excitoniques. Cependant, des difficultés techniques ont empêché la réalisation de microcavités à base de ZnO pendant longtemps. Dans cette thèse nous présentons la fabrication de microcavités à base de ZnO par deux approches différentes, ce qui a permis de surmonter les difficultés technologiques existantes et ont permis d'obtenir des figures de mérite avec des valeurs records (pour le facteur de qualité ainsi que pour l’éclatement de de Rabi). Des lasers à polaritons fonctionnant à température ambiante ont été démontré dans les deux cas. Dans la microcavité entièrement hybride, des condensats de polaritons ont été étudiés dans une gamme de désaccord exciton-photon sans précédents, et de basse température à température ambiante; ceci a permis d'obtenir, pour la première fois, un diagramme de phases complet. Cette thèse ouvre la voie à une polaritonique appliquée fonctionnant à température ambiante. / Cavity polaritons are quasi-particles, partially light partially matter, resulting from the strong-coupling of an exciton and a cavity photon. At a certain temperature and particle density, cavity polaritons can go through a quasi-Bose-Einstein phase transition and condense at the lowest energy state of the system; in this situation the cavity emits coherent light and the associated device is termed polariton laser. ZnO is one of the most adapted materials for fabricating room temperature polariton lasers, due to its excellent excitonic properties. However, technical difficulties have been preventing the achievement of ideal ZnO microcavities for a long time. In this thesis we report the fabrication of high quality ZnO microcavities with two different approaches, which overcome the existing technical challenges and allow to achieve a record cavity quality factor and large Rabi splittings. Room temperature polariton lasing has been demonstrated in both cases. In a fully-hybrid ZnO microcavity, polariton condensates were studied within an unprecedented range of exciton-photon detunings, and from low to room temperature. This tunability has enabled to obtain, for the first time, a complete condensation phase diagram for ZnO-based microcavities, wherein the exciton fraction of the polaritons has been tuned between 17% to 96%, corresponding to a modification of the exciton-polariton mass, its lifetime and its interaction constant by 1 order of magnitude. This thesis paves the way for implementing a polariton-based technology operating at room-temperature.

Active plasmonics combines the manipulation of light on both sub-wavelength length and ultrashort time scales, a unique meld that holds promise for developments in many scientific fields. This thesis reports on a novel approach to ultrafast, all-optical control of grating-assisted excitation of surface plasmon polaritons based on opto-thermally modifying the optical properties of gold. In contrast to prior works, this approach results in plasmonic modulation on picosecond and even sub-picosecond time scales, and is compatible with modern, multi-GHz information processing technology. Finally, an analytic model is developed that allows for the rapid and accurate calculation of the coupling efficiency of beams with arbitrary spatial profile. First, the ultrafast dynamics of existing plasmonic coupling resonances, on gold films with grating overlayers, are studied with spectrally resolved pump-probe measurements. Irradiation of the metal by 700 fs, 775 nm laser pulses results in modulations of the plasmonic coupling efficiency of ~20% near the center, or ~60% off-center, of resonances centered between 540 nm and 700 nm. The modulations decay with a time constant of 770 +/- 70 fs. The experimental results are consistent with simulations based on the thermal-dynamics of the electron-lattice gold system, coupled with numerical modeling of light-grating interactions. Next, two 150 fs, 810 nm laser beams are interfered on the surface of a planar gold film, leading to an absorption/refraction grating in the metal. Optical pump-probe spectroscopy measurements of the first (-1) diffracted order in transmission identify plasmonic coupling resonances between 520 nm and 570 nm. The observed coupling efficiency is ~10^{-5}, and the launch window decays with a time constant of 620 +/- 100 fs. Lastly, a Green function-based analytic model is developed to describe grating assisted plasmonic coupling, culminating in a first-order differential equation with coefficients that have both clear physical significance as well as analytic forms. Comparison of this technique with standard numerical modeling methods shows that plasmonic coupling efficiencies in excess of 0.8 are predicted within an error of 15%. This model is used to study plasmonic excitation by finite-size beams, showing the spatial evolution of the intensity of both the surface plasmon polariton and the reflected beam.

Active plasmonics combines the manipulation of light on both sub-wavelength length and ultrashort time scales, a unique meld that holds promise for developments in many scientific fields. This thesis reports on a novel approach to ultrafast, all-optical control of grating-assisted excitation of surface plasmon polaritons based on opto-thermally modifying the optical properties of gold. In contrast to prior works, this approach results in plasmonic modulation on picosecond and even sub-picosecond time scales, and is compatible with modern, multi-GHz information processing technology. Finally, an analytic model is developed that allows for the rapid and accurate calculation of the coupling efficiency of beams with arbitrary spatial profile. First, the ultrafast dynamics of existing plasmonic coupling resonances, on gold films with grating overlayers, are studied with spectrally resolved pump-probe measurements. Irradiation of the metal by 700 fs, 775 nm laser pulses results in modulations of the plasmonic coupling efficiency of ~20% near the center, or ~60% off-center, of resonances centered between 540 nm and 700 nm. The modulations decay with a time constant of 770 +/- 70 fs. The experimental results are consistent with simulations based on the thermal-dynamics of the electron-lattice gold system, coupled with numerical modeling of light-grating interactions. Next, two 150 fs, 810 nm laser beams are interfered on the surface of a planar gold film, leading to an absorption/refraction grating in the metal. Optical pump-probe spectroscopy measurements of the first (-1) diffracted order in transmission identify plasmonic coupling resonances between 520 nm and 570 nm. The observed coupling efficiency is ~10^{-5}, and the launch window decays with a time constant of 620 +/- 100 fs. Lastly, a Green function-based analytic model is developed to describe grating assisted plasmonic coupling, culminating in a first-order differential equation with coefficients that have both clear physical significance as well as analytic forms. Comparison of this technique with standard numerical modeling methods shows that plasmonic coupling efficiencies in excess of 0.8 are predicted within an error of 15%. This model is used to study plasmonic excitation by finite-size beams, showing the spatial evolution of the intensity of both the surface plasmon polariton and the reflected beam.

Zugl.: Bremen, Univ., Diss., 2006

Universiẗat, Diss., 1999--Marburg.

A tunable polarization modulator based on the periodic metal strips embedded in a polymer waveguide is presented. The periodic metallic structure is analyzed by Finite Element simulation (COMSOL). The calculation results show that the giant birefringence is formed by the selective cut-off of TE polarization over TM polarization, which makes it possible to design an efficient polarization modulator with a short conversion length. The metallic strips are made by using four-layer lift-off fabrication technology. The transmission and group indices of TE and TM modes are measured. However, it is observed that TE and TM modes cut off at same time, which does not agree with our predictions. The reason for failure is that the change in refractive indices is different from what we expected, which makes the device perform in opposite way. Finally, further suggestions are provided to modify the design so that the device can achieve its expected function.

A tunable polarization modulator based on the periodic metal strips embedded in a polymer waveguide is presented. The periodic metallic structure is analyzed by Finite Element simulation (COMSOL). The calculation results show that the giant birefringence is formed by the selective cut-off of TE polarization over TM polarization, which makes it possible to design an efficient polarization modulator with a short conversion length. The metallic strips are made by using four-layer lift-off fabrication technology. The transmission and group indices of TE and TM modes are measured. However, it is observed that TE and TM modes cut off at same time, which does not agree with our predictions. The reason for failure is that the change in refractive indices is different from what we expected, which makes the device perform in opposite way. Finally, further suggestions are provided to modify the design so that the device can achieve its expected function.

In this thesis, original theoretical and numerical investigations into the interaction of light with excitonic nanostructures are presented, in a bid to demonstrate that excitonic nanostructures are viable alternatives to the use of plasmonic nanostructures where electric field enhancement and confinement are sought. In particular, the field enhancement and confinement around excitonic nanostructures on resonance is shown to be comparable if not in excess of that around noble metal nanoparticles such as gold and silver. These excitonic modes, when set in the context of a core-shell geometry, are shown to offer tunability through nanoparticle design and through the index of the environment. In addition, hybrid `hyperbolic' and `plexcitonic' modes are shown to offer similar properties in metallic-excitonic nanostructures. Altogether, these excitonic and hybrid excitonic modes are shown to have potential in nanophotonic applications.