Ce travail de thèse a démontré la possibilité de mesurer la relaxation d’un complexe biomoléculaire ainsi que son hétérogénéité structurale, en associant la microfluidique et la fluorescence résolue en temps (FRT). Je présente de quelle façon la FRT permet d’obtenir une information sur la structure d’une molécule et comment on la mesure, notamment grâce à une caméra à balayage de fente. J’introduis ensuite la microfluidique de gouttes, permettant de mélanger deux réactifs en quelques millisecondes et de suivre la relaxation du complexe au cours de la propagation des micro-réacteurs. Puis, la mesure d’une cinétique avec un couple de molécules modèle démontre la preuve de principe, faisant l’objet d’un article soumis. Enfin la mesure de FRT par comptage de photons uniques dans des gouttes uniques est décrite. Elle ouvre une perspective d’application pour le criblage à haut débit : un brevet a été déposé. / This thesis has proven the feasibility of measuring the relaxation of a biomolecular complex as well as its structural heterogeneity, by associating microfluidics and time resolved fluorescence (TRF). I present in which way TRF allows for probing the structure of a molecule and how it is measured, in particular by using a streak camera. I then introduce droplet microfluidics, which enables to mix two reagents in a few milliseconds and to follow the relaxation of the complex, along propagation of the micro-reactors. Next, the measurement of a kinetics with test molecules validates the proof of concept, reported in a submitted article. Finally, the measurement of TRF by single photon counting in single droplets is described. It opens a perspective for an application in high-throughput screening: a patent has been registered.

Ces travaux de thèse portent sur l’étude de différents phénomènes non-linéaires ayantlieu dans le domaine térahertz (THz) au sein de cristaux de structure zinc-blende.En premier lieu, nous avons mis en place au laboratoire deux sources de rayonnementTHz intense, aux caractéristiques temporelles et spectrales bien distinctes. La premièrerepose sur le redressement optique d’une impulsion laser de durée femtoseconde dansun cristal de niobate de lithium, et la seconde est, quant à elle, basée sur la créationd’un plasma par focalisation d’un champ optique compos´e de l’impulsion fondamentalede pompe et de son second harmonique. Ces deux sources permettent de générer desondes THz dont l’amplitude est bien adaptée à la mise en oeuvre d’expériences d’optiquenon-linéaire.Nous avons ensuite caractérisé le comportement non-linéaire de cristaux de structurezinc-blende soumis à des champs THz intenses. Nous nous sommes ainsi intéressés àl’effet Pockels lors de l’interaction d’une impulsion THz intense et d’un champ optiquede faible intensité, dit sonde, au sein du matériau. Ceci nous a conduits à démontrerexpérimentalement et numériquement la possibilité de caractériser la phase spectrale del’impulsion sonde, à l’aide d’une technique équivalente au X-FROG. Nous avons égalementidentifié l’existence d’un processus non-linéaire dit de cascade, consistant en la générationde second harmonique induite par effet Pockels. Enfin, nous avons observé expérimentalementl’apparition d’un effet Kerr THz dans le cristal, nous permettant de déduire unevaleur moyenne de la susceptibilité non-linéaire du troisième ordre de ce matériau, `a l’aidede calculs théoriques et de simulations numériques. / This thesis project aims to study different non-linear processes in zinc-blende crystals,which take place in the terahertz (THz) range.First of all, two different light sources have been built in the laboratory, allowing us togenerate intense THz radiations with different temporal and spectral characteristics. Thefirst source is based on the optical rectification of a femtosecond laser pulse in a lithiumniobate crystal using the tilted pulse front technique, while the second one is based on aplasma, created through the focalization of a two-color femtosecond laser field. These twoTHz sources reach very high amplitudes, which allows us to study non-linear phenomenain the THz range.Among these, we have measured the non-linear behavior of zinc-blende crystals underintense THz radiation. We were particularly interested in the Pockels effect happeningduring the interaction of an intense THz field and a weak optical probe beam. This droveus to the experimental and numerical demonstration of a new method to characterize thespectral phase of the optical probe field. This method is equivalent to the X-FROG technique.We also identified a new non-linear phenomenon, consisting of the cascade of twosecond-order processes, namely the Pockels effect and the Second Harmonic Generation.Finally, we experimentally observed some THz Kerr effect in a gallium phosphide crystal,which allowed us to calculate an average value of its third-order non-linear susceptibility,thanks to theoretical considerations and simulations.

<p>Laser-induced plasmas since their discovery in the 1960’s have found numerous applications in laboratories and industries. Their uses range from soft ionization source in mass spectroscopy, development of compact particle accelerator, and X-ray and deep UV radiation sources to diagnostic techniques such as laser-induced breakdown spectroscopy and laser electronic excitation tagging. In addition, the laser-induced plasma is important for studying of various nonlinear effects at beam propagation, such as laser pulse filamentation.</p> <p>This work deals with two challenging aspects associated with laser-induced plasmas. First is the study of Multi-Photon Ionization (MPI) as a fundamental first step in high-energy laser-matter interaction critical for understanding of the mechanism of plasma formation. The second is application of laser induced plasma for diagnostics of combustion systems.</p> <p>Numerous attempts to determine the basic physical constants of MPI process in direct experiments, namely photoionization rates and cross-sections of the MPI, were made; however, no reliable data was available until now, and the spread in the literature values often reached 2–3 orders of magnitude. This work presents the use of microwave scattering in quasi-Rayleigh regime off the electrons in the laser-induced plasma as method to measure the total number of electrons created due to the photoionization process and subsequently determine the cross-sections and rates of MPI. Experiments were done in air,<i> O₂, Xe, Ar, N₂, Kr</i>, and <i>CO</i> at room temperature and atmospheric pressure and femtosecond-laser pulse at 800 nm wavelength was utilized. Rayleigh microwave scattering (RMS) technique was used to obtain temporally resolved measurements of the electron numbers created by the laser. Numbers of electrons in the range 3 × 10⁸–3 × 10¹² were produced by the laser pulse energies 100–700 <i>μ</i>J and corresponding electron number densities down to about 10¹⁴ cm^-3 in the center of laser-induced spark were observed. After the laser pulse, plasma decayed on the time scale from 1 to 40 ns depending on the gas type and governed by two competing processes, namely, the creation of new electrons from ionization of the metastable atoms and loss of the electrons due to dissociative recombination and attachment to oxygen. </p> <p>Diagnostics of combustion at high pressures are challenging due to increased collisional quenching and associated loss of acquired signal. In this work, resonance enhanced multiphoton photon ionization (REMPI) in conjunction with measurement of generated electrons by RMS technique were used to develop diagnostics method for measuring concentration of a component in gaseous mixture at elected pressure. Specifically, the REMPI-RMS diagnostics was developed and tested in the measurements of number density of carbon monoxide (<i>CO</i>) in mixtures with nitrogen (<i>N₂</i>) at pressures up to 5 bars. Number of REMPI-induced electrons scaled linearly with <i>CO</i> number density up to about 5×10¹⁸ cm^-3 independently of buffer gas pressure up to 5 bar, and this linear scaling region can be readily used for diagnostics purposes. Higher <i>CO</i> number densities were associated laser beam energy loss while travelling through the gaseous mixture. Four (4) energy level model of <i>CO</i> molecule was developed and direct measurements of the laser pulse energy absorbed in the two-photon process during the passage through the <i>CO</i>/<i>N₂</i> mixture were conducted in order to analyze the observed trends of number of REMPI-generated electrons with <i>CO</i> number density and laser energy.</p>

Diese Arbeit beinhaltet experimentelle und theoretische Untersuchungen der optischen Frequenzverdopplung (second-harmonic generation, kurz SHG) an metallischen Nanopartikeln. Frequenzverdopplung bedeutet, daß ein bei der Frequenz omega angeregtes Nanopartikel Strahlung der Frequenz 2*omega emittiert. Dieser Effekt tritt nicht nur in Materialien mit nichtzentrosymmetrischer Kristallstruktur, sondern auch an der Oberfläche von Metallen auf. Deshalb läßt er sich gut mit plasmonischen Feldüberhöhungen an metallischen Nanoantennen verbinden. Die Frequenzverdopplung wird an verschiedenen Nanostrukturen wie dreieckförmigen, stäbchenförmigen und vor allem kegelförmigen Nanopartikeln experimentell untersucht, welche aufgrund ihrer scharfen Spitzen starke SHG-Signale emittieren. Besonders die Kegel sind interessant: Bei Anregung mit einem fokussierten, radial polarisierten Strahl dominiert je nach Kegelgröße und Umgebungsmedium ein SHG-Signal entweder von der Spitze oder von der Bodenkante des Kegels. Diese an den Kegeln gemessenen Resultate werden durch theoretische Untersuchungen untermauert. In diesen Rechnungen werden die plasmonischen Feldüberhöhungen und die sich daraus ergebende Frequenzverdopplung für einen Kegel mit verschiedenen Parametern modelliert. An einem einzelnen Kegel gewonnene Resultate werden auch mit den Fällen eines kugelförmigen und eines stäbchenförmigen Partikels verglichen. Ein weiterer Gegenstand der theoretischen Untersuchungen ist die Superposition der zweiten Harmonischen von mehreren emittierenden Nanopartikeln zu einem Feldmaximum. Dabei wird eine kreisförmige Anordnung von 8 Nanostäbchen bzw. Nanokegeln von einer radial polarisierten Mode angeregt. Die Superposition der emittierten zweiten Harmonischen ergibt ein Feldmaximum innerhalb der Anordnung der Emitter. Durch eine Verkippung des anregenden Strahls kann dieser Fokus im Raum bewegt werden. Letztere Untersuchung ist insbesondere interessant im Hinblick auf lokalisierte photochemische Reaktionen, die durch das frequenzverdoppelte Licht von Nanopartikeln ausgelöst werden sollen. Mit chemischen Substanzen, die bei omega transparent, bei 2*omega aber photoreaktiv sind, wäre im Nahfeld dieser Nanoantennen eine starke Lokalisierung der Reaktion auf Bereiche kleiner als 100~nm möglich. Anhand von Photolacken und Polymermatrizen mit diesen Eigenschaften wird experimentell untersucht, ob frequenzverdoppeltes Licht überhaupt solche Reaktionen auslösen kann oder ob die photochemische Reaktionen überwiegend durch direkte Zwei-Photonen-Absorption des anregenden Lichts ausgelöst werden. Die Ergebnisse zeigen allerdings, daß die Zwei-Photonen-Absorption dominant ist. Durch die Zwei-Photonen-Absorption im Nahfeld von Partikeln ist aber dennoch eine vergleichbare Lokalisierung der Reaktion möglich.:1. Einführung 1.1 Frequenzverdopplung an Nanopartikeln 1.2 Photochemisches Schreiben auf kleinen Längenskalen 2. Theoretische Grundlagen 2.1 Nichtlineare optische Effffekte zweiter Ordnung 2.2 Frequenzverdopplung in Metallen 2.3 Frequenzverdopplung bei metallischen Nanopartikeln 2.4 Überlagerung der Strahlung mehrerer frequenzverdoppelter Dipole 2.5 Core-Shell-Nanopartikel mit nichtzentrosymmetrischem Kern 3. Experimenteller Aufbau 3.1 Beleuchtung der Proben und Detektionspfad 3.2 Objektiv und Probenhalter 3.3 Realisierung der radial polarisierten Mode 4. Messungen der zweiten Harmonischen an Nanostrukturen 4.1 Einzelne kugel- und stäbchenförmige Goldnanopartikel 4.2 Nanodreiecke (Fischer-Pattern) 4.3 Nanokegel 4.4 Nanostäbchen-Teppiche 4.5 Zusammenfassung 5. Nichtlinear-optisches photochemisches Schreiben auf kleinen Längenskalen 5.1 Photochemische Reaktionen auf der Sub-100nm-Skala 5.2 Erste Versuche an Photolacken 5.3 Photochemisches Schreiben auf azobenzolhaltigen PMMA-Copolymerschichten 5.4 Photochemisches Schreiben auf azosulfonathaltigen PMMA-Copolymerschichten 5.5 Ausblick 6. Zusammenfassung und Ausblick Anhang A. Darstellung der radialen Mode und des z-polarisierten Fokus B. Mehode der multiplen Multipole (MMP) C. Präparation der Proben Literaturverzeichnis Abbildungsverzeichnis Verzeichnis der Tabellen Verwendete Abkürzungen Liste der Veröffffentlichungen Danksagung Erklärung / This work includes experimental and theoretical investigations of second-harmonic generation (SHG) at metallic nanoparticles. SHG means that a nanoparticle that is excited at the frequency omega emits radiation at the frequency 2*omega. SHG does not only occur in materials with noncentrosymmetric structure, but also on metal surfaces. Hence, SHG can be combined well with plasmonic field enhancement at metallic nanoantennae. SHG is investigated experimentally at different nanostructures such as triangle-like, rod-like and especially cone-like nanoparticles. With their sharp tips these structures show a much stronger SHG signal than spherical nanoparticles. Especially the cones are interesting: Excited with a focused radially polarized beam, for different cone sizes and in different surrounding media either the signal from the tip or the signal from the bottom edge dominates. The measurement results from the cones are underpinned by theoretical investigations. In these calculations the plasmonic field enhancements and the resulting SHG are modeled for a cone with different parameters. The single-cone results are also compared with the cases of a spherical or rod-shaped particle. A further subject of the theoretical investigations is the superposition of the SHG radiation from a number of emitting nanoparticles to a field maximum. For that, a circular arrangement of 8 nanorods or nanocones is excited by a radially polarized beam. The superposition of the second-harmonic radiation fields yields a field maximum in the space between the emitters. A tilt of the exciting beam can move this focus in space. The latter item is of special interest concerning localised photochemical reactions induced by the second-harmonic light from nanoparticles. In the near field of these nanoantennae, a strong localisation of the reaction on regions smaller than 100 nm would be possible by using chemical substances being transparent at omega, but photoreactive at 2*omega. With photoresists and polymer matrices, experiments are carried out to investigate whether SHG light can trigger such reactions at all, or if these photochemical reactions are triggered predominantly by direct two-photon absorption of the exciting light. The results show that the two-photon absorption is the dominant process. Yet, through two-photon absorption in the near field of particles, the localisation of the reaction is still similar.:1. Einführung 1.1 Frequenzverdopplung an Nanopartikeln 1.2 Photochemisches Schreiben auf kleinen Längenskalen 2. Theoretische Grundlagen 2.1 Nichtlineare optische Effffekte zweiter Ordnung 2.2 Frequenzverdopplung in Metallen 2.3 Frequenzverdopplung bei metallischen Nanopartikeln 2.4 Überlagerung der Strahlung mehrerer frequenzverdoppelter Dipole 2.5 Core-Shell-Nanopartikel mit nichtzentrosymmetrischem Kern 3. Experimenteller Aufbau 3.1 Beleuchtung der Proben und Detektionspfad 3.2 Objektiv und Probenhalter 3.3 Realisierung der radial polarisierten Mode 4. Messungen der zweiten Harmonischen an Nanostrukturen 4.1 Einzelne kugel- und stäbchenförmige Goldnanopartikel 4.2 Nanodreiecke (Fischer-Pattern) 4.3 Nanokegel 4.4 Nanostäbchen-Teppiche 4.5 Zusammenfassung 5. Nichtlinear-optisches photochemisches Schreiben auf kleinen Längenskalen 5.1 Photochemische Reaktionen auf der Sub-100nm-Skala 5.2 Erste Versuche an Photolacken 5.3 Photochemisches Schreiben auf azobenzolhaltigen PMMA-Copolymerschichten 5.4 Photochemisches Schreiben auf azosulfonathaltigen PMMA-Copolymerschichten 5.5 Ausblick 6. Zusammenfassung und Ausblick Anhang A. Darstellung der radialen Mode und des z-polarisierten Fokus B. Mehode der multiplen Multipole (MMP) C. Präparation der Proben Literaturverzeichnis Abbildungsverzeichnis Verzeichnis der Tabellen Verwendete Abkürzungen Liste der Veröffffentlichungen Danksagung Erklärung

Dans ce travail de thèse, je considère deux phénomènes distincts, tous deux liés aux interactions non-linéaires entre la lumière et des atomes. La première partie est dédiée à du mélange à 4 ondes basé sur des degrés de liberté internes d’atomes d’hélium à température ambiante, et l’utilise pour des processus d’amplification et de la génération d’états comprimés. Le second phénomène étudié est basé sur des degrés de liberté externes d’atomes de césium froids et est utilisé pour du stockage de lumière et la génération d’un champ conjugué en phase par mélange d’ondes. J'ai expérimentalement observé et caractérisé de l'amplification sensible à la phase par mélange à quatre ondes dans de l'hélium métastable à température ambiante. J'ai obtenu un gain maximum d'environ 9 dB avec une bande passante d'environ 300 kHz. Les fonctions de transfert phase/phase obtenues ont montré une forte compression de phase, indiquant que le phénomène était presque exempt de processus indésirables. Dans la seconde partie, j'explique comment les résonances de recul, dues à un transfert de quantité de mouvement entre un photon et un atome, peuvent être utilisées pour du stockage de lumière. J'explique également comment ce phénomène peut conduire à la génération d’un champ conjugué, et pourquoi la théorie existante ne permet pas de modéliser le creux qui apparaît dans le spectre de génération du champ conjugué lorsqu’on augmente la puissance optique. Pour reproduire ce nouvel élément, j’ai effectué un développement jusqu’au 5e ordre, qui démontre qu’il dépend de la cohérence qui est excitée entre des niveaux de moments atomiques différents. Je montre ensuite qu'un modèle plus simple, basé sur trois niveaux atomiques définis par des degrés de liberté interne et externe de l'atome, peut expliquer le phénomène observé. / In this PhD work, two distinct phenomena are considered, which are both related to non-linear interactions between light and atoms. The first part of the thesis is dedicated to four wave mixing based on the internal degrees of freedom of room temperature helium atoms and uses it for amplification processes and generation of squeezed light. The second studied process is based on external degrees of freedom of cold cesium atoms and used for light storage and phase conjugate field generation through multi-wave mixing. I experimentally observed and characterized phase sensitive amplification via four-wave mixing in metastable helium at room temperature. I have obtained about 9 dB of maximum gain with a bandwidth of about 300 kHz. The obtained phase transfer functions showed a strong phase squeezing, indicating that the phenomenon was almost free of unwanted processes. In the second part, I explain how recoil induced resonances, which are due to the transfer of momentum between a photon and an atom, can be used to store light. I also explain how this phenomenon can lead to generation of a phase conjugate field, and why the existing theory fails to model the dip, which appears in the phase conjugate generation spectrum when the field power is increased. I extend the model to the fifth order so that it can reproduce this new feature and demonstrate that it depends on the decay rate of the coherence, which is excited between atomic levels of different momenta. I then show that a simpler model, which is based on three levels defined by internal and external degrees of freedom of the atom, can explain the observed phenomenon.

No description available.

Diode lasers are a convenient and economical source of near-infrared radiation, which may usefully be applied to a host of different sensitive detection methods; this thesis presents novel extensions of these methods, making use of the favourable characteristics of this type of light source. The first part of this thesis details the development of an optical feedback cavity-enhanced absorption spectroscopy (OF-CEAS) apparatus, including the development of the optical system, the sample handling, and the electronics for feedback phase control. A preliminary demonstration of the system is reported, presenting the detection of atmospheric water absorptions close to 1596 nm. Optimisation and application of the OF-CEAS spectrometer are then demonstrated, after which the spectrometer is applied to the sensitive detection of carbon dioxide absorptions suitable as a diagnostic aid in identifying Heliobacter pylori infection. A time-normalised α-min value of 5.8 × 10⁻⁹ cm⁻¹s^1/2 was measured for these spectra. Further optimisation of the system leads to an ultimate detection sensitivity of 1.42 × 10⁻⁹ cm⁻¹s^1/2, measured on absorption transitions in acetylene close to 1532 nm. In order further to characterise the performance of the OF-CEAS system, analogous experiments are presented using the OF-CEAS setup and a standard diode-laser cavity-enhanced absorption spectroscopy (CEAS) apparatus. Detection is carried out on the P(6) line of the ν₁ + ν₃ vibrational band of the mixed isotopologue of acetylene, ¹²-C¹³-CH₂. Direct comparison is made between the sensitivities of the two methods, and in light of this the suitability of each technique for detection in different environments is considered. The well-characterised and consistent frequency scale which is inherent to the OF-CEAS technique is then applied to a line shape analysis for the presented absorption spectra. Pressure-broadening coefficients are determined for selected absorptions in the ν₁ + ν₃ band of acetylene. In spite of the low resolution associated with this technique, this accurate frequency scaling allows observation of subtle line shape effects such as Dicke collisional narrowing using the data presented in Chapter 3 for the R(60) line in the 3ν₁ + ν₃ vibrational band of CO₂. These effects are quantified through use of a Galatry fit to each absorption spectrum. The statistical significance associated with the use of such a model, and the physical meaning of the results, are examined and discussed. An alternative strategy for increasing the sensitivity of a diode-laser-based gas monitoring technique lies in moving detection to the mid-infrared region, where the absorption cross-sections are generally larger. With this motivation, difference frequency generation is presented, to produce radiation close to 3.5 µm which is then applied to a series of different enhanced spectroscopy techniques. The optimal sensitivity, of 32 ppb NO2 at 45 Torr total sample pressure, was achieved using wavelength modulation spectroscopy. The different techniques are compared and possible improvements to them are put forward. Finally, proof-of-principle work is presented seeking to combine the enhanced circulating power associated with the optical-feedback-locked techniques and non-linear optical techniques to move detection to a more favourable spectral region. Light close to 429 nm is generated by second harmonic generation in a crystal of potassium niobate, with resonance-enhancement afforded by a feedback V-cavity of the sort employed in OF-CEAS. The potential of such a system for diode-laser-based generation of blue and ultraviolet light is demonstrated and discussed, along with improvements that might be implemented to increase the efficiency of the system.

This thesis presents work examining the characteristics and applicability of quantum cascade lasers. An introduction is given explaining both the desire for a widely tunable, narrow bandwidth device working in the midinfrared, as well as detailing the ways in which quantum cascade lasers (QCLs) fulfill these requirements. The development and manufacture of QCLs are then discussed. The experimental section of this thesis is then split into three parts. Chapter 2 concerns the characterisation and application of several pulsed QCLs. The intrapulse mode of operation is employed and the effect of the resulting rapid frequency chirp upon molecular spectra is investigated in the form of rapid passage signals. The evolution of said rapid passage signals is then investigated as a function of chromophore pressure and identity, with different QCLs, chirp rates, and optical path lengths. The prospect of producing population transfer with chirped lasers is discussed. Chapters 3, 4, and 5 are then concerned with the application and characterisation of continuous wave QCLs. In these chapters a widely tunable commercially produced EC-QCL is utilised as well as two DFB QCLs, one of which is used in tandem with a home-made mount and temperature controller. In Chapter 3 a number of sensitive detection techniques are compared with the employment of wavelength modulation spectroscopy, long path cells and optical cavities, and the narrow bandwidth of QCLs utilised to determine a previously unknown spectral constant of DBr. Chapters 4 and 5 then utilise the high power of an external cavity quantum cascade laser in sub-Doppler Lamb-dip and polarisation spectroscopy measurements and then a pump-probe experiment. The laser linewidth is investigated on a millisecond timescale returning a current noise limited value of c.a. 2 MHz and the fundamental linewidth of the device investigated by altering the injection current. Chapter 5 is concerned with the pump-probe experiment, directly measuring the hot band absorption in a ladder like transition (R(6.5)$_\frac{1}{2}$ $v=1\leftarrow0$ and P(7.5)$_\frac{1}{2}$ $v=1\leftarrow0$). The Bennett peak in the hot band is observed with a DFB-QCL swept at $\sim 0.15$ MHz ns$^{-1}$ and is seen not just as a pump bandwidth limited lineshape, but as a highly velocity selected rapid passage signal. The effect of pressure, pump and probe scan rate and power upon this rapid passage signal is also studied. It is further noted that rapid thermalisation occurs within $v=1$ such that at pressures above c.a. 30 mTorr a broad NO doublet absorption is observed beneath the Bennett peak from which a total population transfer of c.a. $16 \%$ can be estimated. Finally an experiment is discussed in which this population transfer could be increased for use in secondary applications. Chapter 6 then presents initial measurements with two prototype pulsed 3.3 \si{\micro\metre} QCLs considering the prospects of such devices. A Fabry-P\'rot device is first studied using a Fourier transform spectrometer and temperature tuning used to produce a spectrum of the Q-branch of CH$_4$ around 3025 cm$^$. Experiments are then performed using a DFB QCL investigating the chirp rate of the system as an indicator of the rate of heat accumulation within the system. Heat management is of particular consideration when the sea-change is made from pulsed to continuous devices. For this device absorption spectra of two CH$_4$ transitions at 2971 cm$^$ are used to determine the chirp rate, which is found to be c.a. 1.8 GHz ns$^$, at least an order of magnitude higher than that of the longer wavelength pulsed devices considered in Chapter 2.

En passant de l’état massif à la nanoparticule les matériaux métalliques voient certaines de leurs caractéristiques modifiées de manière notable comme par exemple les propriétés optiques avec l’apparition d’une résonance dans le spectre optique, la Résonance Plasmon de Surface Localisée (RPSL) responsable du changement de couleur des nanoparticules métalliques. Les propriétés vibrationnelles et thermiques de nanoparticules métalliques ont été étudiées à l’aide d’une technique de Spectroscopie Femtoseconde. Nous avons montré qu’il était possible d’exciter et de détecter optiquement des fréquences de vibrations mécaniques dans le domaine térahertz pour des nanoparticules de platine composées de moins de cent atomes. D’autre part l’augmentation des effets dus aux interfaces a été mis en évidence sur les propriétés thermiques de nanoparticules d’or et d’argent. La résistance thermique à l’interface, résistance de Kapitza, voit son rôle augmenter lors du transfert thermique à l’échelle nanométrique. Une corrélation entre les valeurs mesurées et les impédances acoustiques des matériaux composants les interfaces a été mise en évidence. Nous avons aussi montré qu’elle augmente quand la température diminue de 300K à 70K. Les propriétés optiques de nanoparticules non sphériques ont été étudiées à l’aide de la Spectroscopie à Modulation Spatiale. Cette technique a permis de repérer puis de caractériser des nano-bâtonnets d’or individuels. Nous avons montré que la largeur spectrale de la RPSL est fortement dépendante de la géométrie des nanoparticules (diamètre et longueur). Cette double dépendance n’est pas prédite par les modèles classiques ou quantique existants / The size reduction of metals, from bulk to nanoparticles, induces significant modifications of their properties. For instance, the optical properties evolve and a new resonance, the localized surface plasmon resonance, appears in the optical spectrum and is responsible for the change of colors of metallic nanoparticles. This work is focused on studies of metals’ properties at the nanometric scale. In the first part, the vibrational and thermal properties are studied with a femtosecond spectroscopy technique. It is shown that it is possible to excite and detect optically vibrational frequencies in the terahertz domain by studying platinum nanoparticles formed by less than 100 atoms. The study of the thermal properties of the metallic nanoparticles (gold and silver) has shown that the boundary effect increases. This thermal boundary resistance, known as the Kapitza resistance, plays a dominant role in the heat transfer at the nanometric scale. A correlation between the experimental values of the thermal boundary resistance and the acoustic impedances of the boundary’s materials has been found. We have also shown that the Kapitza resistance is a decreasing function of the temperature in the 70-300K range. In the second part, the effect of the size reduction on the optical properties of non-spherical nanoparticles is observed. The Spatial Modulation Spectroscopy technique is used in order to locate and study individual gold nanorods. It is shown that the two geometrical parameters (the length and the diameter) of the nanorods influence the spectral linewidth of the localized surface plasmon resonance. This effect is not predicted by existing classical or quantum models

Ce manuscrit expose le développement de ressources fondamentales pour les communications quantiques à longues distances basées sur les technologies des fibres optiques télécoms et des guides d'onde optiques non linéaires. Après une introduction générale sur les communications quantiques, cette thèse est structurée en trois parties principales. La première partie illustre le développement de deux sources pour la génération de paires de photons intriqués en polarisation et émis à une longueur d'onde télécom via conversion paramétrique spontanée (SPDC) dans des guides d'ondes non linéaires intégrés sur niobate de lithium périodiquement polarisé. Les sources s'appuient respectivement sur un accord de phase de type-II et un accord de phase de type-0 et sur des solutions de filtrage et d'interférométrie mises en place après le cristal non linéaire. Dans la seconde partie, sont discutées les réalisations de deux sources de photons uniques annoncés haut débit. La première s'appuie sur le multiplexage spatial sur puce de photons uniques annoncés. La seconde exploite le multiplexage temporel passif grâce à l'utilisation d'un laser télécom cadencé à 10 GHz. Enfin, nous présentons une approche tout-optique visant la synchronisation de sources distantes de paires de photons intriqués, agencées selon une architecture de type relais quantique distribué. Cette technique innovante repose sur l'utilisation d'un laser télécom impulsionnel en tant qu'horloge optique de référence. Cette horloge autorise la synchronisation de l'émission de paires de photons dans la bande C des télécoms en deux lieux distants. Des résultats préliminaires d'interférence à deux photons sont montrés et discutés. / This manuscript reports the development of fundamental resources for long distance quantum communication based on fibre telecom technology and non-linear optical waveguides. After a general introduction on quantum communication, the thesis is structured along three parts. The first part illustrates the development of two photonic polarization entanglement sources suitable for quantum networking. Both sources generate paired photons at telecom wavelength via spontaneous parametric down conversion (SPDC) in periodically poled lithium niobate waveguides (PPLN/W). They rely on type-II and type 0 phase matching, respectively. In the second part, two high quality heralded single photon sources are highlighted. The first one relies on on-chip generation and spatial multiplexing of heralded single photons towards achieving higher bit rates. The second one takes advantage of passive temporal multiplexing of a single SPDC process. Finally, an all-optical approach towards efficient and accurate synchronization of remote entangled photon pair sources within quantum relay architecture over long distances is presented. This particular synchronization technique highlights the use of ultra-fast picosecond pulsed telecom fiber laser, operating at 2.5 GHz repetition rate, acting as a master optical clock, enabling to accurately synchronize the emission of photon pairs in the telecom C-band of wavelengths at two remote locations. This innovative approach is applied for synchronizing two remote PLLN/W based sources operated at 2.5 GHz, and preliminary results on two-photon interference obtained with single photons coming from each source are shown and discussed.