Práce se zabývá teorií nelineární spektroskopie a projevy kvantové koherentní dynamiky v nelineární spektroskopii. Poskytuje stručný přehled spektroskopických metod se zaměřením na metodu pump-probe. Dále rozví- jíme teorii nelineární odezvy, přičemž vycházíme z obecného N-wave mixing experimentu, a dospíváme ke tvaru odezvové funkce třetího řádu vyjádřené pomocí Liouvillových drah. Pro vybrané modelové systémy sledujeme koher- entní efekty, které se projevují v 2D a pump-probe spektrech, a provádíme jejich porovnání. D·raz je kladen na objasnění jev· relaxace a excitonové koherence mezi dvěma excitovanými stavy molekulárního dimeru. 1

L’intégration des communications optiques sur puce offre de vastes promesses en termes de performances et de réduction de la puissance consommée, les canaux optiques ne souffrant pas des nombreuses limitations des canaux métalliques. De plus, l’information codée optiquement permet d’atteindre des débits de données élevés par le biais du multiplexage en longueur d’onde. Afin de conserver la compatibilité avec les composants électroniques, les communications et composants optiques doivent s’intégrer dans la filière silicium. Cependant, ce dernier matériau ne permet pas d’envisager la réalisation de certaines fonctions optiques, en particulier la source laser. D’autres matériaux doivent ainsi être intégrés pour suppléer au silicium. Mes travaux de thèse portent sur l’intégration de nanotubes de carbone sur plate-forme silicium pour la photonique. Dans ces travaux, le potentiel des nanotubes de carbone pour la réalisation de sources optiques intégrées est exploré. Dans un premier temps, je proposerai des pistes de compréhension de l’apparition du gain optique dans les nanotubes de carbone semiconducteurs par analyse des temps de vie des excitons, mesurés en spectroscopie pompe-sonde. Ces temps de vie sont sensiblement rallongés lorsque la centrifugation des nanotubes de carbone, au cours de l’extraction, est poussée à des vélocités et des temps plus longs. Une explication envisagée est la réduction du nombre de défauts à la surface des nanotubes, ces défauts se comportant comme des centres de recombinaison non-radiatifs. D’autre part, une méthode efficace d’intégration des nanotubes de carbone sur guide d’onde silicium a été proposée. Cette méthode robuste et permet d’observer le couplage de la photoluminescence des nanotubes de carbone avec le mode optique du guide d’onde. Afin d’obtenir une interaction exaltée entre mode optique et nanotube de carbone, le couplage entre les nanotubes et différentes cavités photoniques, incluant microdisques, cavités Fabry-Pérot et micro-résonateurs en anneau, a été étudié. L’emploi en particulier de résonateurs en anneau permet d’observer la structuration de la photoluminescence des nanotubes de carbone par les modes de résonance de l’anneau. Différentes configurations ont été étudiées afin de compléter la compréhension des mécanismes de couplage : micro-photoluminescence, photoluminescence guidée et photoluminescence intégrée. / On-chip optical communication may increase drastically performances and consumption of communication systems. Indeed, optical channels do not face limitations that metallics interconnects do. Even better would be the achievable data rate due to the multiplexing possibility in optics. In order to keep compatibility with electronic devices, optical components and interconnects should be built in silicon. However, this material is not suitable for some optical function, such as laser sources. Thus, there is a need to integrate alternative materials to compensate for silicon weaknesses. My PhD work focuses on integration of carbon nanotube on silicon for photonics applications. In this work, potential use of carbon nanotube for light emission function is investigated. First, I will propose clue to understand the appearance of optical gain in semiconducting carbon nanotube. Such investigation is done by mean of pump-probe experiments, where the excitons lifetimes are measured. Those lifetimes slightly increase while centrifugation time and speed is increased, during the extraction process. A possible explanation is that defect-free carbon nanotubes are selected by the centrifugation process. In parallel, I worked on designing an efficient method to couple nanotubes photoluminescence with silicon waveguides. This method appears to be quite robust, and allows to observe coupling between the nanotube photoluminescence and the optical mode of the waveguide. In order to obtain a more intense interaction between the optical mode and carbon nanotubes, I investigated the coupling between carbon nanotubes and several photonic cavities, including microdisks, Fabry-Pérot cavities and ring resonators. Specifically, ring resonators allow to measure the photoluminescence of carbon nanotube structured by the resonant modes. Several configurations are studied to understand more in-depth the coupling mechanisms: micro-photoluminescence, guided photoluminescence and integrated photoluminescence.

All-optical time-resolved measurement techniques provide a powerful tool for investigating critical parameters that determine the performance of infrared photodetector and emitter semiconductor materials. Narrow-bandgap InAs/GaSb type-II superlattices (T2SLs) have shown great promise as a next generation source of these materials, due to superior intrinsic properties and versatility. Unfortunately, InAs/GaSb T2SLs are plagued by parasitic Shockley-Read-Hall recombination centers that shorten the carrier lifetime and limit device performance. Ultrafast pump-probe techniques and time-resolved differential transmission measurements are used here to demonstrate that Ga-free InAs/InAsSb T2SLs and InAsSb alloys do not have this same limitation and thus have significantly longer carrier lifetimes. Measurements at 77 K provided minority carrier lifetimes of 9 μs and 3 μs for an unintentionally doped mid-wave infrared (MWIR) InAs/InAsSb T2SL and InAsSb alloy, respectively; a two order of magnitude increase compared to the 90 ns minority carrier lifetime measured in a comparable MWIR InAs/GaSb T2SL. Through temperature-dependent lifetime measurements, the various carrier recombination processes are differentiated and the dominant mechanisms identified for each material. These results demonstrate that these Ga-free materials are viable options over InAs/GaSb T2SLs for potentially improved infrared photodetectors. In addition to carrier lifetimes, the drift and diffusion of excited charge carriers through the superlattice growth layers (i.e. vertical transport) directly affects the performance of photodetectors and emitters. Unfortunately, there is a lack of information pertaining to vertical transport, primarily due to difficulties in making measurements on thin growth layers and the need for non-standard measurement techniques. However, all-optical ultrafast techniques are successfully used here to directly measure vertical diffusion in MWIR InAs/GaSb T2SLs. By optically generating excess carriers near one end of a MWIR T2SL and measuring the transit time to a thin, 2 lower-bandgap superlattice placed at the other end, the time-of-flight of vertically diffusing carriers is determined. Through investigation of both unintentionally doped and p-type superlattices at 77 K, the vertical hole and electron diffusion coefficients are determined to be 0.04±0.03 cm2/s and 4.7±0.5 cm2/s, corresponding to vertical mobilities of 6±5 cm2/Vs and 700±80 cm2/Vs, respectively. These measurements are, to my knowledge, the first direct measurements of vertical transport properties in narrow-bandgap superlattices. Lastly, the widely tunable two-color ultrafast laser system used in this research allowed for the investigation of nonlinear optical properties in narrow-bandgap semiconductors. Time-resolved measurements taken at 77 K of the nondegenerate two-photon absorption spectrum of bulk n-type GaSb have provided new information about the nonresonant change in absorption and two-photon absorption coefficients in this material. Furthermore, as the nondegenerate spectrum was measured over a wide range of optical frequencies, a Kramers-Kronig transformation allowed the dispersion of the nondegenerate nonlinear refractive index to be calculated.

The research presented has been focused on understanding the surface effects on the optical and electronic properties of some metallic and semiconductor nanomaterials. When the particle sizes are on the nanometer length scale, a large fraction of atoms in the particles are on the surface. The bonding of the surface atoms being unsaturated could cause trapping and introduce defects that interact with the excited electrons. The effect of the surface on the optical and electronic properties of some semiconductor and metallic nanoparticles is investigated. When the size and shape of nanomaterials change, both the electron density of the excited electrons on the surface and the electronic structure change. Therefore, it becomes important to understand how these changes affect the electronic motion in the particles in order to exploit their full potential in a variety of applications. Semiconductor nanoparticles studied include cadmium selenide (CdSe) and cadmium sulfide (CdS). Effect of changing CdSe shape and size on optical and electronic properties has been investigated and the ability for the CdS nanoparticles to show optical gain (stimulated emission) in solution at room temperature is reported. Effect of surface phonon contribution on the exited electron relaxation in copper nanoparticles is investigated. For the particles size smaller than the mean free path of the electrons in the metal, electron-surface phonon coupling becomes an important factor (contribution) for hot electron relaxation. In the thesis presented, it is shown for the first time the size depended electronic relaxation in copper nanoparticles. Fluorescence due to surface plasmon field enhancement is observed for copper nanoparticles to be million times stronger than the fluorescence observed from bulk copper.

We have studied fundamental aspects of photo-induced dissociation kinetics and dynamics in several phenyl halides. By combining femtosecond pump-probe measurements with ab initio calculations we are able to account for several observations. In mixed phenyl halides, the dissociation kinetics is found to be dependent on the nature, the number, and the position of the substituents, and also on the excitation wavelength. A surprisingly large reduction in the dissociation time constant, compared to that of bromobenzene (~30 ps), is observed when having two or more fluorine atoms. For example, in bromopentafluorobenzene a subpicosecond time constant is obtained. This can be explained by a significant lowering of the repulsive potential energy curves (PEC) along the C-Br bond. However, several of the experimental results cannot be accounted for by one-dimensional PECs. Therefore, we suggest a refined model for the dissociation, in which the excited states of the same spin multiplicity are coupled by employing multidimensional potential energy surfaces. This model has been explicitly evaluated by quantum dynamics simulations in the case of 3-BrFPh, and it seems to be capable of capturing the main features in the measured kinetics. Thereby we are also able to clarify the role of spin-orbit coupling in these molecules.

In this thesis, we investigate the nature of charge carrier generation, relaxation and recombination in a range of lead halide perovskites. We focus on understanding whether the photophysical behaviour of these perovskite materials is like that of highly-ordered inorganic crystalline semiconductors (exhibiting ballistic charge transport) or disordered molecular semiconductors (exhibiting strong electron-phonon coupling and highly localised excited states) and how we can tune these photophysical properties with inorganic and organic additives. We find that the fundamental photophysical properties of lead halide perovskites, such as charge carrier relaxation and recombination, arise from the lead halide lattice rather than the choice of A-site cation. We show that while the choice of A-site cation does not affect these photophysical properties directly, it can have a significant impact on the structure of the lead halide lattice and therefore affect these photophysical properties indirectly. We demonstrate that lead halide perovskites fabricated from particular inorganic and organic A-site cation combinations exhibit low parasitic trap densities and enhanced carrier interactions. Furthering our understanding of how the photophysical properties of these materials can be controlled through chemical composition is extremely important for the future design of highly efficient solar cells and light emitting diodes.

Ce travail analyse la formation d'états liés par interaction coulombienne d'excitons dans un ensemble de nanotubes de carbone de chiralité (6,5) en solution. Sous l'action d'une impulsion laser de forte intensité, une grande densité d'excitons est formée dans le nanotube et conduit à la formation d'état de trion et de biexciton. Les mécanismes physiques responsables de la photogénération de ces états ont été analysés dans le cadre de cette thèse. Ces travaux sont effectués à l'aide d'une expérience pompe-sonde dans laquelle le faisceau sonde est un continuum de lumière blanche permettant ainsi l'observation simultanée des états d'exciton, de trion et de biexciton. Cela conduit à l'obtention des énergies de liaison des différentes contributions excitoniques. En outre la dynamique de ces états excitoniques a aussi pu être obtenue avec une résolution temporelle de l'ordre de la centaine de femtosecondes. / In this thesis, we have studied the excitonic bound states formation in an ensemble of chirality (6,5) carbon nanotubes in solution. Under intense laser excitation, a large density of excitons is reached in the nanotube. This leads to the formation of bound states such as trion and biexciton. The physical mecanisms responsible for the photogeneration of these states have been analysed in this thesis. We performed a pump-probe experiment using a white light continuum as the probe beam. This allows the simultaneous observation of the excitonic, trion and biexciton states which gives information about the binding energies of the bound states. Finally, we also studied the dynamics of these excitonic bound states that have been obtained with a temporal resolution close to hundred of femtoseconds.

In this thesis we present a study about strong light-matter interaction in a broad single GaAs/AlGaAs quantum well representing a 3-level system. In particular we investigate the AC-Stark effect, where we observe in THz absorption spectra an Autler-Townes splitting as well as a Mollow-triplet. Compared to previous work, we showed for the first time an all-THz pump-probe experiment in the THz regime below the Reststrahlenband. Furthermore, we observe a strong frequency shift in the absorption energy of the first intersubband transition depending on the charge carrier density in the quantum well. The Autler-Townes splitting as well as the absorption frequency shift can be potentially exploited for THz-modulation applications. Beyond nonlinear optics many interesting effects occur in the strong light-matter interaction regime such as Rabi oscillations, coherent population trapping, lasing without inversion, electromagnetically induced transparency (EIT) and the AC-Stark effect. Our quantum well represents a 3-level system in which we investigate a splitting behaviour in the absorption spectrum of the first and second intersubband transition. Especially a splitting for the first intersubband transition is predicted also for electromagnetically induced transparency, while the second intersubband transition is pumped with a strong varying electric field. Naturally, a fundamental question is, how to distinguish EIT and an Autler-Townes duplet since both result in a spectrally transparent window. The method of choice for investigations combines narrowband pulses in the THz range provided by a free-electron laser and broadband THz pulses generated in a GaP crystl within a THz time-domain spectroscopy setup. In this unique configuration we perform time-resolved pump and probe spectroscopy experiments by pumping resonantly the second intersubband transition at 3.4 THz to induce a splitting of the second and third subband. Broadband THz pulses then probe an absorption splitting of about 0.2 THz related to the first intersubband transition at ≈ 2.3 THz as well as a splitting of the second intersubband transition (Mollow triplet). Analyzing experiments and using a theoretical criteria to distinguish EIT and Autler-Townes splitting, we conclude to observe an Autler-Townes doublet instead of an EIT effect. / In dieser Arbeit berichten wir über die starke Licht-Materie Wechselwirkung in 3-Niveau system anhand eines einzelnen, breiten GaAs/AlGaAs Quantentopfes. Insbesondere untersuchen wir den AC-Stark Effekt und beobachten eine Aufspaltung des Absorptionsspektrums durch das Autler-Townes Dublett und das Mollow Triplett. Im direkten Vergleich mit vorangegangenen Arbeiten zeigen wir zum ersten Mal ein reines THz Anrege-Abfrage Experiment mit Frequenzen unterhalb des Reststrahlenbandes. Weiterhin beobachten wir eine starke Frequenzverschiebung der Absorptionsenergie des ersten Intersubbandübergangs in Abhängigkeit von der Ladungsträgerdichte im Quantentopf. Sowohl das Autler-Townes Dublett als auch die Verschiebung der Absorptionsfrequenz ermöglichen potentielle Anwendung im Bereich der THz-Modulation. Im Bereich der starken Licht-Materie Wechselwirkung sind viele interessante Effekte beobachtbar wie Rabi Oszillationen, coherent population trapping, Lasern ohne Inversion, elektromagnetisch induzierte Transparenz (EIT) und der AC-Stark Effekt. Unser Quantentopf stellt ein 3-Niveau System dar, in welchem wir eine Aufspaltung der Absorption bezüglich des ersten und zweiten Intersubbandübergangs beobachten. Insbesondere für den ersten Intersubbandübergang ist auch eine Absorptionsaufspaltung durch den EIT Effekt vorhergesagt, während der zweite Intersubbandübergang durch ein starkes, elektrisches Wechselfeld angeregt wird. Es stellt sich dann die Frage, wodurch sich die Effekte EIT und Autler-Townes splitting unterscheiden, weil beide durch ein spektrales transparentes Fenster gekennzeichnet sind. Die von uns gewählte Methode verknüpft schmalbandige, starke elecktrische Wechselfelder im THz-Bereich eines freien Elektronen Lasers und breitbandigen THz-Pulsen, welche durch nichtlineare optische Effekte in einem THz Zeit-Bereichs Spektroskopie Aufbaus erzeugt werden. In dieser einzigartigen Konfiguration führen wir zeitaufgelöste Anrege-Abfrage Spektroskopie Experimente durch, in dem wir den zweiten Intersubbandübergang bei 3, 4 THz nahezu resonant anregen und das zweite und dritte Subband aufspalten. Mit breitbandigen THz Pulsen fragen wir dann die Absorptionsaufspaltung von ca. 0, 2 THz des ersten Intersubbandübergangs bei ≈ 2, 3 THz und des zweiten Intersubbandübergangs (Mollow-Triplett) ab. Nach Auswerten der Experimente und theoretischer Kriterien für die Unterscheidung zwischen EIT und Autler-Townes splitting schlussfolgern wir, ein Autler-Townes Dublett zu beobachten.

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