La peau est un organe qui enveloppe le corps, elle est une barrière naturelle importante et efficace contre différents envahisseurs. Pour le traitement des maladies dermatologiques ainsi que dans l'industrie cosmétique, les applications topiques sur la peau sont largement utilisées. Ainsi beaucoup d'efforts ont été investis dans la recherche sur la peau visant à comprendre l'absorption moléculaire et les mécanismes rendant efficace la pénétration. Cependant, il reste difficile d'obtenir une visualisation 3D de haute résolution combinée à une information chimique- ment spécifique et quantitative dans la recherche sur la peau. La spectroscopie et la microscopie non-linéaire, incluant la fluorescence excitée à 2-photon (TPEF), la diffusion Raman spontanée, la diffusion Raman cohérente anti-Stokes (CARS) et la diffusion Raman stimulée (SRS), sont introduits dans ce travail pour l'identification sans ambiguïté de la morphologique de la peau et la détection de molécules appliquées de façon topique. Plusieurs méthodes quantitatives basées sur la spectroscopie et la microscopie non-linéaire sont proposées pour l'analyse chimique en3D sur la peau artificielle, ex vivo et in vivo sur la peau humaine. De plus, afin de s'adapter aux applications cliniques à venir, un design endoscopique est étudié pour permettre l'imagerie non-linéaires dans les endoscopes flexibles. / Skin is an organ that envelops the entire body, acts as a pivotal, efficient natural barrier to- wards various invaders. For the treatment of major dermatological diseases and in the cosmetic industry, topical applications on skin are widely used, thus many efforts in skin research have been aimed at understanding detailed molecular absorption and efficient penetration mechanisms. However, it remains difficult to obtain high-resolution visualization in 3D together with chemical selectivity and quantification in skin research. Nonlinear spectroscopy and microscopy, including two-photon excited fluorescence (TPEF), spontaneous Raman scattering, coherent anti-Stokes Raman scattering (CARS) and stimulated Raman scattering (SRS), are introduced in this work for unambiguous skin morphological identification and topical applied molecules detection. Sev- eral quantitative methods based on nonlinear spectroscopy and microscopy are designed for 3D chemical analysis in reconstructed skin, ex vivo and in vivo on human skin. Furthermore, to adapt to forthcoming clinical applications, an endoscopic design is investigated to bring nonlin- ear imaging in flexible endoscopes.

Doctor of Philosophy / Department of Physics / B.D. DePaola / In recent years, coherent excitation techniques have focused on the ability to efficiently prepare atomic or molecular systems into a selected state. Such population control plays a key role in cutting-edge research taking place today, such as in the areas of quantum information and laser-controlled chemical reactions. Stimulated Raman adiabatic passage (STIRAP) is a widely-used coherent excitation technique that provides a relatively robust control mechanism for efficiently exciting a target population into a desired state. While the technique is well proven, current experimental techniques yield little information on the population dynamics taking place throughout the excitation process, and experimentalists rely solely on final excited-state measurements to determine the efficiency of population transfer. This dissertation presents a unique diagnostic tool to measure multilevel coherent population transfer on a short (nanosecond) timescale. The technique described here uses magneto-optical trap recoil ion momentum spectroscopy (MOTRIMS) as a noninvasive probe of a coherently-controlled system. It provides extremely detailed information about the excitation process, and highlights some important characteristics seen in excited populations that would otherwise be misleading or completely overlooked if one were to use more traditional diagnostic techniques. This dissertation discusses both the theoretical and experimental results applied to three-level coherently excited target populations of Rb-87.

Contemporary laser research involves the development of spectroscopic techniques to understand the microscopic structural aspects of a simple molecular system in chemical and materials to more complex biological systems such as cells. In particular, Raman spectroscopy, which provides bond specific information, has attracted considerable attention. Further with the advent of femtosecond (fs) laser, the recent trend in the field of fs chemistry is to develop nonlinear Raman techniques that allow one to acquire vibrational structural information with both fs temporal resolution as well as good spectral resolution. Among many advanced nonlinear Raman techniques, the development of fs Stimulated Raman scattering (SRS) has gathered momentum in the recent decade due to its ability to (1) provide vibrational structural information of various system including fluorescent molecules with good signal to noise ratio and (2) circumvent the limitation imposed on the spectral resolution by the necessary pulse durations according to the energy-time uncertainty principle where ‘K’ is a constant that depends on the pulse shape) unlike in the case of fs normal resonance Raman spectroscopy. We have developed a technique named “Ultrafast Raman loss spectroscopy (URLS)” that is analogues to SRS, but is more advantageous as compared to SRS and has the potential to be an alternative if not competitive tool as a vibrational structure elucidating technique. The concept and the design of this novel technique, URLS, form the core of the thesis entitled “Ultrafast Raman Loss Spectroscopy (URLS)”. Chapter 1 lays the theoretical groundwork for ultra-short pulses and nonlinear spectroscopy which forms the heart of URLS. It presents a detailed discussion on the basis behind the elementary experimental problems associated with the ultra-short laser pulses when they travel through a medium, the characterization of these ultrashort pulses as well as various non-linear phenomena induced within a medium due to the propagation of these pulses. Chapter 2 focuses on the concept of SRS which resulted into the foundation of URLS. It illustrates the theoretical as well as the experimental aspects of SRS and demonstrates the sensitivity of SRS over normal Raman spectroscopy. Chapter 3 introduces the conceptual and the technical basis which ensued into the development of URLS while Chapter 4 demonstrates its application and efficiency over its analogue SRS. URLS involves the interaction of two laser sources, viz. a picosecond (ps) pulse and a fs white light (WL), with a sample leading to the generation of loss signal on the higher energy (blue) side with respect to the wavelength of the ps pulse unlike the gain signal observed on the lower energy (red) side in SRS. These loss signals are at least 1.5 times more intense than SRS signals. Also, the very prerequisite of the experimental protocol for signal detection to be on the higher energy side by design eliminates the interference from fluorescence, which appears on the red side. Thus, the rapid data acquisition, 100% natural fluorescence rejection and experimental ease ascertain “Ultrafast Raman Loss Spectroscopy (URLS)” as a unique valuable structure determining technique. Further, the effect of resonance on the line shape of the URLS signal has been studied which forms the subject of discussion in Chapter 5. The objective of the study is to verify whether the variation of resonance Raman line shapes in URLS could provide an understanding of the mode specific response on ultrafast excitation. It is found that the URLS signal’s line shape is mode dependent and can provide information similar to Raman excitation profile (REP) in the normal Raman studies. This information can have impact on the study of various dynamical process involving vibrational modes like structural dynamics and coherent control. Chapter 6 demonstrates the application of URLS as a structure elucidating technique for monitoring ultrafast structural and reaction dynamics in both chemical and biological systems using α-terthiophene (3T) as the model system. The objective is to understand the mechanism of the molecular structure dependent electronic relaxation of the first singlet excited state, S1, of α-terthiophene using fs URLS. The URLS data along with the ab-initio calculations indicate that the electronic transition is associated with a structural rearrangement from a non-planar to a planar configuration in the singlet manifold along the ring deformation co-ordinate. The experimental findings suggest that the singlet state decays exponentially with a decay time constant ( 1/e) of about 145 ps and this decay could be assigned to the intersystem crossing (ISC) pathway from the relaxed S1 state to the vibrationally hot triplet state, T1*. Lastly, Chapter 7 summarizes the entire thesis and presents some possible future prospects for URLS. Considering the advantages of URLS, it is proposed that URLS can be exploited [1] to determine the structure of any fluorescent/non-florescent condensed materials and biological systems with a very good spectral resolution (10- 40 cm-1); [2] to obtain the vibrational signature of weak Raman scattering molecules and vibrational modes with relatively small Raman cross-section owing to its high detection sensitivity with good signal to noise ratio; [3] for performing fs time-resolved study by introducing an additional fs pulse for photo-excitation of the molecule and using URLS to probe the excited state dynamics with good temporal (fs) and spectral (10-40 cm-1) resolution; and lastly, [4] the high chemical selectivity of URLS and the fact that the signal is generated only within the focal volume of the lasers where all the beams overlap can be utilized for developing this method into a microscopy for labeled-free effective vibrational study of biological samples. Consequently, it is hoped that this technique, “Ultrafast Raman Loss Spectroscopy (URLS)”, would be a suitable alternative to other nonlinear Raman methods like coherent anti-Stokes Raman spectroscopy (CARS) that has made major inroads into biology, medicine and materials.

Nonlinear optical microscopy is a collection of very powerful imaging techniques. Linear optical microscopes probe the refractive index and absorption, which both stem from the first-order linear electric susceptibility. Especially in biological tissue, the variation in the refractive index is often small and the tissue is, in many cases, transparant. Nonlinear optical microscopes on the other hand probe the nonlinear higher-order susceptibilities, which can be chemically sensitive, leading to the capability to achieve label-free imaging. Nonlinear optical microscopes have been in development for more than thirty years and they are based on numerous nonlinear optical processes. The ones I will concentrate on in this thesis are second harmonic generation (SHG), coherent anti-Stokes Raman scattering (CARS), and stimulated Raman Scattering (SRS). The first technique is commonly used to image collagen as those molecules have a particularly large second-order nonlinear susceptibility due to their chiral structure. CARS and SRS on the other hand are often used because they resonantly target vibrational resonances in molecules, giving rise to the aforementioned label-free imaging. Deep understanding of the nonlinear imaging process is crucial to the interpretation of the images these techniques produce. Computational tools are exceptionally suited for this task as they allow studying the electromagnetic field anywhere in the sample as well as the far-field, and one can change any of the material properties to study their effect. One such tool is finite-difference time-domain (FDTD) that our group developed for nonlinear optical microscopy simulations. It is a direct discretization of Maxwell's equation. While computationally costly, it does allow any arbitrary shaped sample to be simulated. The sample can have frequency dependent refractive indexes, and also nonlinear media with third-order nonlinearities such as Kerr media and Raman-active media, but also second-order nonlinearities for SHG. The code is designed in such a way that it can run on thousands of CPUs on a wide variety of compute cluster which allows our group to obtain nanoscale resolution. Another computational tool I use is the free-space Green's function solution to the Helmholtz equation, which can be used to calculate the Hertz vector in the frequency domain, both in the near- and far-field, based on the induced nonlinear polarization. The electric field is then calculated from this Hertz vector. This technique is much faster then FDTD and also allows for arbitrary shapes of the nonlinear electric susceptibility in the sample. However, it assumes a homogeneous refractive index throughout the entire spatial domain and requires complete knowledge of the input beam or beams that induce the nonlinear polarization. In this thesis, I use these tools to study the image formation process of various nonlinear optical processes mentioned earlier. For example, I study the effect of an inhomogeneous refractive index on the images produced by these microscopes. In literature the index of refraction is almost always assumed to be homogeneous, because, as mentioned before, the inhomogeneity of the refractive index is often small. However, I show that these small differences in the index of refraction can have a significant effect on the measured far-field intensity signal. For example, in SRS and CARS images, the measured signal can increase by an order of magnitude depending on the index mismatch and structure of the sample. Additionally, significant shifts in perceived position occur. Even nonresonant nonlinear signals can be evoked purely through a mismatch in linear refractive index. Computational modelling can also help reveal additional detail. As SHG is a coherent process, subwavelength information can be inferred through the phase information. Our experimental collaborators built an interferometric SHG (I-SHG) microscope for exactly that purpose. We used this to image collagen fibrils, which are all aligned in a parallel fashion. However, because collagen fibrils have a chiral molecular structure, they can point either ``up'' or ``down''. Using my Green's function simulations of the SHG imaging process of collagen fibrils, I was able to predict the standard deviation in the measured phase and link it to the orientation of collagen fibrils in the focal spot of the probing laser beam, even though the diameters are far below the minimum resolvable capabilities of the microscope. We found that the ``upwards'' fibrils make up 46--53% of the sample. Even with a normal SHG microscope that does not measures phase, additional subresolution information is obtainable. With our collaborators we measured the ratio of the forward SHG intensity signal to that in the backward direction and with my simulations, we are able to link this to the fibril diameters in collagen tissue. Thus we inferred that the fibril diameter increases as a function of tissue depth. Furthermore, a computational technique called ptychography is able to retrieve phase information without an interferometric reference beam. Additionally, it increases resolution to the theoretical limit, independent of the laser focal spot size, and corrects for distortions in the input beam as well. I have developed this technique for use with nonlinear optical microscopy and was able to show it is a viable alternative to I-SHG by imaging simulated rat tail tendon at the diffraction limit while retrieving the orientation of the fibrils through the phase of the SHG signal. I also implemented the algorithm for CARS, where the phase information can be used to greatly increase the signal-to-noise ratio by reducing the nonresonant background radiation that results from competing nonlinear optical processes. I showed an example of this by imaging a simulated fibroblast cell where the CARS process was tuned to the lipid droplets inside of the cell. I am currently in talk with experimentalists to apply this theoretical technique to experiments as that would further demonstrate the impact of my work. Finally, keeping in theme with the collagen fibrils, I show that the ratio of the forward SHG signal to the backward signal, the F/B ratio, is affected by a mismatch in the refractive index for fibrils larger than 100nm. This measure is an indicator of fibril diameter and thus important for making qualitative predictions. Single fibrils are generally too small to be significantly affected by near-field effects, but the bigger fibrils can be. Fibrils in rat tail tendon have a distribution of fibrils diameters and the large fibrils occur infrequent. However, I found that the large fibrils are largely responsible for the forward as well as backward signal, thus refractive index mismatches still affect the F/B ratio significantly despite their infrequency. The F/B ratio for a collection of fibrils placed in a n=1.47 medium was found to be 31.8±0.7% higher than for those in a n=1.33 medium. Our experimental colleagues have done preliminary measurements on mouse tail tendon where they found an increase of 40±20%, in line with the value of 28.1±0.6% that I found for simulations with mouse tail tendon. In conclusion, the theoretical tools I have used in my thesis have provided me with the ability to study nonlinear optical image formation processes with a level of detail that would be near-impossible to do experimentally. I have used this ability to show how refractive index mismatches, such as those found in biological tissue, can significantly distort the far-field intensity signals. I have shown this for SRS and CARS where the far-field intensity signal appeared an order-of-magnitude larger compared to the same sample without a refractive index mismatch with the background medium. Additionally, shifts in the perceived position of the object under investigation were observed and I showed the presence of a nonresonant background signal in AM-SRS. Likewise I showed that in the SHG imaging of collagen fibrils significant changes in the F/B ratio can occur. All of these effects have important implications as these types of images as biomedical researches rely on the correct interpretation of nonlinear optical microscopy images for both research and diagnostics. Apart from showing the effect of a refractive index mismatch, I have also shown that computation modelling can be used to infer subwavelength features in SHG imaging experiments of collagen fibril such as fibril orientation and fibril diameter. These methods have the potential to aid medical researchers as changes in the structure of collagen are often an early indicator of diseases such as osteoarthritis. Finally, I showed that the ptychography algorithm I developed for nonlinear optical microscopy is able to retrieve phase information of the nonlinear electric susceptibility in SHG and CARS imaging while also enhancing the resolution and correcting for distortions in the input beams. I can also use much larger laser spot sizes than in conventional experiments without compromising the obtained resolution, thus fewer measurements are required. The technique is not limited to SHG and CARS either; it will work for other nonlinear optical processes as well. Experimental verification of nonlinear ptychography will be done soon. This technique has to potential to significantly improve current imaging techniques since access to the phase information allows one to observe additional information about the sample as we showed with the I-SHG microscope.

Raman spectroscopy involves change in the polarizability of the molecular system on excitation and is based on scattering process. Spontaneous Raman scattering is a two photon process, in which the input light initiates the excitation, which then leads to an emission of another photon due to scattering. It is extensively used to understand molecular properties. As spontaneous Raman scattering is a weak process, the detection of these weak Raman photons are rather difficult. Alternatively, resonance Raman (RR) scattering is another technique where the excitation wavelength is chosen according to the material under study. The excitation wavelength is chosen to be within the absorption spectrum of the material under study. RR spectroscopy not only provides considerable improvement in the intensity of the Raman signal, but also provides mode specific information i.e. the modes which are Franck-Condon active in that transition can be observed. There are reports on RR studies of many systems using pulsed light as an excitation source. It is necessary to use at least two pulsed laser sources for carrying out the time resolved RR spectroscopy. A single pulse source for excitation would lead to compromise either with temporal or spectral resolution which is due to the uncertainty principle. If an excitation pulse has pulse width of ~100 femtoseconds then the spectral resolution will be ~ 150 cm-1. It is clear now that for improving the temporal and spectral resolution simultaneously, usage of single pulse for Raman experiments (spontaneous scattering) is not adequate. The usage of multiple laser pulses may provide the way out to improve the resolutions. Nonlinear spectroscopy in a broad view helps in understanding the structural and dynamical properties of the molecular systems in a deeper manner. There are a number of techniques as a part of nonlinear spectroscopy that have emerged in due course to meet different requirements and to overcome some difficulties while understanding the molecular properties. Stimulated Raman (SRS) gain, coherent anti-Stokes Raman scattering (CARS) and the inverse Raman spectroscopy are a few to mention as third order nonlinear spectroscopic techniques which give the similar kind of information about the molecular systems. Stimulated Raman scattering is a more general process involved in nonlinear Raman processes. SRS involves at least two laser pulses and the difference in their frequencies should match with the vibrational frequency of the molecule. The polarization has to be matched between the Raman pump and the Raman probe pulses. We have developed a new nonlinear Raman technique in our laboratory named as ultrafast Raman loss spectroscopy (URLS) using the principles of nonlinear Raman scattering. It involves the Raman pump (~ 1 picosecond (ps) or ~ 15 cm-1spectral resolution) and Raman probe as a white light continuum (100 fs) whose frequency components ranges from 400-900 nm. The laser system consists of Tsunami which is pumped by a Millennia laser and Spitfire-Pro, a regenerative amplifier which is pumped by an Empower laser. Tsunami provides a 100 fs, 780 nm centered, 80 MHz and ~6 nJ energy laser pulses. The Tsunami output is fed into Spitfire to amplify its energy and change the repetition rate to 1 KHz. The pulse length of the input pulse is preserved in amplification. The output of amplifier is split into two equal parts; one part is used to pump the Optical Parametric Amplifier (OPA) in order to generate wavelengths in the range 480-800 nm. The output of the OPA is utilized to generate Raman pump which has to be in ps in order to get the best spectral resolution. A small portion of the other part of amplifier output is utilized to generate white light source for the Raman probe. The remaining part of the amplifier output is used to pump TOPAS to generate wavelengths in the ultraviolet region. URLS has been applied to many molecular systems which range from non-fluorescent to highly fluorescent. URLS has been demonstrated to be very sensitive and useful while dealing with highly fluorescent systems. URLS is a unique technique due to its high sensitivity and the Raman loss signal intensity is at least 1.5-2 times higher as compared to the Raman gain signal intensities. Cresyl violet perchlorate (CVP) is a highly fluorescent system. URLS has been applied to study CVP even at resonance excitation. Rhodamine B has also been studied using URLS. Spontaneous Raman scattering is very difficult to observe experimentally in such high quantum yield fluorescent systems. The variation in the lineshapes of the Raman bands for different RP excitation wavelengths in URLS spectra shows the mode dependent behavior of the absorption spectrum. The experimental observation of variation in the lineshape has been accounted using theoretical formalism. The thesis is focused on discussing the development of the new nonlinear Raman spectroscopic technique URLS in detail and its applicability to molecular systems for better understanding. A theoretical formalism for accounting the uniqueness of URLS among the other nonlinear Raman techniques is developed and discussed in various pictorial representations i.e. ladder, Feynman and closed loop diagrams. A brief overview of nonlinear spectroscopy and nonlinear Raman spectroscopy is presented for demonstrating the difference between the URLS and the other nonlinear Raman techniques.

De part ses nombreuses applications scientifiques et sociétales comme la radiographie protonique ou encore la protonthérapie, l’accélération d’ions par laser suscite un grand intérêt. Cette thèse s’inscrit dans ce cadre et présente une étude de l’interaction d’une impulsion laser d’intensité relativiste avec un plasma de densité modérée. Dans ce régime, le plasma est transparent à l’onde laser et les électrons oscillent à des vitesses relativistes dans le champ de l’onde incidente. Ces conditions sont favorables à un transfert efficace de l’énergie laser vers le plasma, et donc sont intéressantes pour l’accélération d’ions par laser. Ce régime permet également la création de solitons électromagnétiques et acoustiques dont les mécanismes de formation et les propriétés nécessitent une meilleur compréhension. Nous réalisons une étude détaillée de simulations Particle-In-Cell (réalisées avec le code OCEAN) de l’interaction d’une impulsion laser intense avec un plasma sous dense. Nous montrons que la diffusion Raman stimulée (SRS) dans le régime relativiste est le principal processus responsable de l’absorption de l’énergie laser par le plasma et qu’il est, en outre, très efficace puisqu’il permet de transférer près de 70 % de l’énergie de l’impulsion laser aux électrons. Cette instabilité apparaît dans des plasmas dont la densité est nettement supérieure à la densité quart-critique du fait de la diminution de la fréquence plasma électronique et se développe sur des temps très courts. Il permet ainsi un chauffage homogène des électrons tout le long de la propagation de l’impulsion laser à travers le plasma. Ces électrons participent à la détente du plasma, et créent sur ses bords raids un champ électrostatique permettant l’accélération des ions. Ces derniers gagnent 30 % de l’énergie laser initiale. Nous avons aussi développé un modèle simple qui permet de prédire et donc d’optimiser le taux de rétro-diffusion du plasma du fait du développement de l’instabilité SRS. Nous nous intéressons également à la séquence des processus permettant la formation des cavités électromagnétiques. Cette analyse souligne le rôle joué par l’instabilité modulationnelle ou de Benjamin-Feir sur le front de l’impulsion laser qui est divisée en un train de plusieurs solitons électromagnétiques. À l’aide d’une étude détaillée, nous montrons que ces solitons excitent des ondes plasmas dans leur sillage en se propageant dans le plasma, perdent de l’énergie et finissent par être piégés. Ils forment également des dépressions (cavités) des densités électroniques et ioniques du plasma. Ces cavités sont des pièges pour les champs électromagnétiques rayonnés par le plasma (par exemple du fait de l’instabilité SRS) et survivent grâce à un équilibre entre la pression de radiation des champs piégés et les pressions cinétiques électroniques à leurs bords. Ces cavités absorbent une part importante de l’énergie laser mais elles n’en conservent qu’une partie sous forme d’énergie électromagnétique piégée. Le reste de l’énergie permet l’expansion de la cavité, la génération de solitons acoustiques supersoniques et l’accélération de particules. / The laser-accelerated ions draw an increasing interest due to their potential applications and to their unique properties. This manuscript presents a study of the interaction between a relativistic intense laser pulse and a low density plasma. In this regime, the plasma is transparent to the laser pulse and electrons oscillate with relativistic velocities in the field of the incident wave. These conditions make the transfer of the laser pulse energy to the plasma efficient, and therefore are interesting for the ion acceleration. This regime generates also electromagnetic and acoustic solitons whose formation mechanisms and properties need to be better understood. We carry out a detailed analysis of Particle-In-Cell simulations (performed with the code OCEAN) of interaction of an intense laser pulse with a low density plasma.We show that the stimulated Raman scattering (SRS) is the main mechanism responsible for the absorption of laser energy in plasma. This process is very efficient : it leads to the transfer of 70 % of the laser pulse energy to electrons. This instability occurs in plasmas with a density larger than the quarter critical one due to the decrease of the electron plasma frequency and develops in a very short time scale. It leads to an homogeneous electron heating all along the distance of propagation of the laser pulse through the plasma. The ions are efficiently accelerated at the plasma edges and can get nearly 30%of the initial laser energy. This study is accompanied by a simple analytical model which is able to predict and so optimize the laser backscattering fraction due to the development of the SRS instability. We also present a sequence of stages which lead to the formation of electromagnetic cavities. This analysis highlights the role of the modulationnal or Benjamin-Feir instability in the front of the laser pulse, which is split in a train of electromagnetic solitons. Our detailed study shows that these solitons excite plasmas waves in their wake, lose energy and are finally trapped in the plasma. They lead to the formation of density depressions (cavities) which may trap the electromagnetic fields produced in the plasma (by the SRS instability, for example). These structures may survive for a long time thanks to an equilibrium of the trapped field radiation pressure and the electronic kinetic pressure at their borders. These cavities absorb an significant part of the laser energy but only a part of it is trapped inside. The remaining part is invested in the cavity expansion, generation of acoustic solitons and acceleration of charged particles.

: cette thèse porte sur l’étude d’un accéléromètre à ondes de matière fonctionnant à bord d’un avion effectuant des vols paraboliques et permettant des expériences en micro-gravité (0-g). Un interféromètre à atomes de 87Rb refroidis par laser, et dont les états quantiques sont manipulés à l’aide de transitions Raman stimulées, constitue l’élément physique du capteur. Lors de la conception du dispositif expérimental, un effort particulier a été apporté au choix d’une source laser transportable, stable, et robuste. Nous démontrons pour la première fois le fonctionnement aéroporté d’un senseur inertiel à ondes de matière, à la fois en 0-g et durant les phases de gravité des vols (1-g). Nous proposons une technique combinant le signal de l’interféromètre à celui d’accéléromètres mécaniques auxiliaires pour effectuer des mesures au dela de la dynamique intrinsèque du capteur atomique. Nous expliquons comment bénéficier du haut niveau de sensibilité de l’interféromètre dans l’avion, et indiquons des voies d’améliorations significatives de notre dispositif pour le futur. En 0-g, nous montrons une amélioration de la sensibilité de l’accéléromètre jusque 2 x 10-4 m.s-2 à une seconde, et étudions une réjection des vibrations de l’avion à l’aide d’un interféromètre à quatre impulsions Raman. L’objectif de notre projet consiste en un test du principe d’universalité de la chute libre avec un double accéléromètre à atomes de 87Rb et de 39K. Notre système laser double-espèce emploie des composants optiques fibrés aux longueurs d’onde de 1.56 et 1.54 μm, ainsi qu’un doublage de fréquence pour obtenir la lumière utile à 780 et 767 nm pour le refroidissement et la manipulation des deux atomes. Nous étudions théoriquement la sensibilité d’une mesure de leur différence d’accélération en tenant compte des vibrations de l’avion, et précisons comment une résolution de l’ordre de 10-10 m.s-2 pourra être atteinte dans le futur avec notre expérience aéroportée. / This thesis reports the study of a matter-wave accelerometer operated aboard a 0-g plane in ballistic flights. The acceleration measurements are performed with a cold 87Rb atom interferometer using stimulated Raman transitions to manipulate the quantum states of the atoms. When designing the instrument, we took special care to make the laser source transportable, robust, and stable. With our setup, we demonstrate the first operation of a matter-wave inertial sensor aboard a plane, both in 0-g and during the gravity phases of the flights (1-g). Thanks to additional mechanical accelerometers probing the coarse inertial effects, we are able to detect acceleration fluctuations much greater than the intrinsic measurement range of the interferometer. We explain our method to benefit from the full sensitivity of the matter-wave sensor in the plane, and suggest significant improvements of our system for the future. In 0-g, we show the enhancement of the accelerometer sensitivity up to 2 x 10-4 m.s-2 in one second, and investigate a rejection of the vibrations of the plane with a four Raman pulses interferometer. The goal of our project is to perform a test of the universality of free fall with two atom accelerometers using 87Rb and 39K. The laser system for the two-species interferometer is based on fiber optical components at wavelengths of 1.56 and 1.54 μm, and optical frequency doubling to generate the useful light at 780 and 767 nm to cool and manipulate the atoms. We study theoretically the sensitivity of the differential acceleration measurement by taking into account the vibrations of the plane, and discuss how a resolution of the order of 10-10 m.s-2 could be achieved in the future with our airborne experiment.

Die Kombination aus Breit-Band Spektroskopie-Methoden ermöglicht eine umfassende Einsicht in das elektronische System von Molekülen im angeregten Zustand. Am Beispiel des Riboflavin in saurer Umgebung wird der Protonen-Transfer aus der Lösung auf den Chromophor mittels transienter Absorption und -Fluoreszenz im S1-Zustand beobachtet. Mittels transienter Absorption- und Femtosekunden-stimulierter Raman-Spektroskopie wird der Populationstransfer in den elektronischen Grundzustand im beta-Karotin verfolgt und charakterisiert werden. / The combination of broadband spectroscopic methods allows a comprehensive view of the electronic system of molecules in the excited state. On riboflavin in acidic environment the proton-transfer is observed with transient absorption and -flurescence in the S1-state. With transient absorption and femtosecond-stimulated Raman-spectroscopy the population transfer into the electronic ground-state is followed and characterized.

Le moment orbital angulaire (OAM) de la lumière est une grandeur quantifiée associée à la phase d’un vortex optique et est actuellement une des variables explorées pour les technologies quantiques.Dans ce contexte, cette thèse étudie expérimentalement la conversion de vortex optiques par une vapeur de rubidium, via la transition Raman stimulée à deux photons 5S₁/₂ − 5D₅/₂. Quand les atomes sont soumis à deux lasers respectivement à 780 nm et 776 nm, ils génèrent des rayonnements cohérents, infrarouge à 5,23 μm et bleu à 420 nm. On examine le rayonnement bleu lorsque l’un des lasers ou les deux sont des vortex, en particulier des modes de Laguerre-Gauss. Dans une première partie nous montrons que si l’OAM est porté par le laser à 776 nm, alors le rayonnement bleu émis porte un OAM qui respecte l’accord de phase azimutale et de phase de Gouy. Nous montrons aussi que la conversion est efficace sur une grande plage d’OAM allant de -50 à +50, que l’efficacité est gouvernée par le produit des intensités des lasers incidents et que le rayonnement bleu se comporte comme un mode de Laguerre-Gauss pur. Dans une deuxième partie nous montrons qu’il est possible de convertir une superposition de vortex ou une paire de vortex coaxiaux et que l’OAM du rayonnement bleu émis obéit à la règle de somme des OAM incidents. Pour les cas étudiés, nous proposons un modèle de mélange à quatre ondes qui établit les règles de sélection du processus de conversion d’OAM. Ce travail ouvre la voie vers la conversion d’OAM utilisant des transitions vers des niveaux atomiques plus élevés. / The orbital angular momentum of light (OAM) is a quantized quantity arising from the azimuthal phase carried by optical vortices and is well-known for quantum technology applications. Its set of values is theoretically infinite.In this context this thesis experimentally study the conversion of optical vortices in a rubidium vapor through the 5S₁/₂ − 5D₅/₂ stimulated Raman transition. When the atoms are illuminated with laser beams at 780 nm and 776 nm they generate two coherent light beams at 5,23 μm and 420 nm. We investigate the blue light when one laser or both are optical vortices, in particular Laguerre-Gaussian modes. In a first part we show that if the laser at 776 nm carries an OAM the blue light is an optical vortex with an OAM which respects azimutal and Gouy phase matchings. We further show that the conversion is efficient on a large set of OAM from -50 to +50, that the efficiency is governed by the product of the input laser intensities and that the blue light behaves like a pure Laguerre-Gaussian mode. In a second part we demonstrate the conversion of a vortex superposition or a pair of coaxial vortices and that the OAM of the emitted light obeys the conservation rule of total OAM. For each studied case we propose a four wave mixing model establishing selection rules for the conversion process. This work opens possibilities towards OAM conversion using higher atomic levels.

Die vorliegende Dissertation befasst sich mit der Anwendung und Weiterentwicklung der CARS -Mikroskopie (CARS, (Coherent anti-Stokes Raman scattering)) zur Lokalisierung von Wirkstoffen in Zellen. Aufgrund einer C-Deuterierung dieser Wirkstoffe werden diese intrinsisch markiert und lassen sich nicht-invasiv mit Hilfe Raman-basierter Mikrospektroskopietechniken von Zellbestandteilen unterscheiden. Diese Arbeit widmet sich der für biomedizinische Anwendungen zu geringen Sensitivität und zu hohen Komplexität des experimentellen Aufbaus für CARS-Mikroskopie. Auf der Anwendungsseite wurdenzunächst mittels quantitativer Raman- und CARS- Mikroskopie die Detektionsgrenzen C-deuterierter Stoffe bestimmt. Anhand von mit deuterierter Fettsäure inkubierter Makrophagen wurde chemischer Kontrast in Zellen qualitativ gezeigt. Die Weiterentwicklung des experimentellen Aufbaus erfolgte durch den Einsatz von Impulsformern. Diese können das Anregungslicht in Amplitude und Phase formen und somit den Schwingungskontrast optimieren und den experimentellen Aufbau vereinfachen. Verwendet wurden dabei sowohl ein spatial light modulator (SLM) als auch ein akustooptischer Modulator (AOM), die in dieser Arbeit miteinander verglichen werden. Mit Hilfe einer photonischen Kristallfaser als spektral breite Lichtquelle und des AOM als spektraler Filter konnte der Aufbau vereinfacht und ein Schema zur Implementierung von Quasi-Multiplex CARS-Mikroskopie aufgebaut werden, welches ein schnelles Schalten zwischen verschiedenen bildgebenden Raman-Banden erlaubt. Die automatisierte Optimierung des Schwingungskontrasts erfolgte schließlich durch den Einsatz des SLM, der mit Hilfe eines selbstlernenden Algorithmus den Schwingungskontrast von CARS-Bildern um bis zu 160 % verbessern konnte.