Radiation damage limits the resolution in imaging experiments. Damage is caused by energy deposited into the sample during exposure. Ultrashort and extremely bright X-ray pulses from free-electron lasers (FELs) offer the possibility to outrun key damage processes, and temporarily improve radiation tolerance. Theoretical models indicate that high detail-resolutions could be realized on non-crystalline samples with very short pulses, before plasma expansion. Studies presented here describe the interaction of a very intense and ultrashort X-ray pulse with material, and investigate boundary conditions for flash diffractive imaging both theoretically and experimentally. In the hard X-ray regime, predictions are based on particle simulations with a continuum formulation that accounts for screening from free electrons. First experimental results from the first soft X-ray free-electron laser, the FLASH facility in Hamburg, confirm the principle of flash imaging, and provide the first validation of our theoretical models. Specifically, experiments on nano-fabricated test objects show that an interpretable image can be obtained to high resolution before the sample is vaporized. Radiation intensity in these experiments reached 10^14 W/cm^2, and the temperature of the sample rose to 60000 Kelvin after the 25 femtosecond pulse left the sample. Further experiments with time-delay X-ray holography follow the explosion dynamics over some picoseconds after illumination. Finally, this thesis presents results from biological flash-imaging studies on living cells. The model is based on plasma calculations and fluid-like motions of the sample, supported by the time-delay measurements. This study provides an estimate for the achievable resolutions as function of wavelength and pulse length. The technique was demonstrated by our team in an experiment where living cells were exposed to a single shot from the FLASH soft X-ray laser.

Röntgen Freie Elektronen Laser ermöglichen es Doppel-K-Schalen Löchern in Molekülen in aufeinanderfolgenden mehrfachen Ionisationsschritten in bedeutender Anzahl zu erzeugen. Die Eigenschaften dieser zweifach ionisierten Zustände ist insbesondere relevant für die Strahlungsschäden bei Beugungsexperimenten mit kohärenter Röntgenstrahlung zur Bildgebung einzelner Moleküle. In dieser Arbeit wird der Auger Zerfall doppelt K-Schalen ionisierter Moleküle mittels quantenchemischer ab-initio Methoden untersucht. Zur Beschreibung des emittierten Auger Elektrons im kontinuierlichen Energiespektrum wird dabei die Ein-Zentrums Methode verwendet, in der die elektronische Wellenfunktion auf einem radialen Gitter beschrieben wird unter Verwendung von sphärischen Harmonischen. Wie anhand desWassermoleküls gezeigt wird, ergeben sich durch die Doppel-K-Loch induzierte Protonendynamik in dem Auger Spektrum ausgeprägte Flanken im höherenergetischen Teil jeder Spektralspitze. Die Lebensdauer von Doppel-K-Schalen Löchern in Molekülen ist deutlich verringert im Vergleich zu einfachen K-Löchern durch die K-Loch induzierten Abschirmeffekte der Valenzelektronen. Dieser Mechanismus wird durch ein einfaches Modell erklärt aus dem eine Beziehung zwischen Zerfallsrate und Valenzelektronenpopulation abgeleitet. Mögliche Konsequenzen dieser Ergebnisse für Röntgenbeugungsexperimente sind: Erstens, auch für Röntgenpulse kürzer als 10fs wird das Beugungsbild durch die K-Loch induzierten Umstrukturierungen der Valenzelektronen beeinflußt. Zweitens, die Gesamt-Ionisationsrate ist erhöht aufgrund der schnelleren Neubesetzung der K-Löcher.

X-ray crystallography has been around for 100 years and remains the preferred technique for solving molecular structures today. However, its reliance on the production of sufficiently large crystals is limiting, considering that crystallization cannot be achieved for a vast range of biomolecules. A promising way of circumventing this problem is the method of serial femtosecond imaging of single-molecules or nanocrystals utilizing an X-ray free-electron laser. In such an approach, X-ray pulses brief enough to outrun radiation damage and intense enough to provide usable diffraction signals are employed. This way accurate snapshots can be collected one at a time, despite the sample molecule exploding immediately following the pulse due to extreme ionization. But as opposed to in conventional crystallography, the spatial orientation of the molecule at the time of X-ray exposure is generally unknown. Consequentially, assembling the snapshots to form a three-dimensional representation of the structure of interest is cumbersome, and normally tackled using algorithms to analyze the diffraction patterns. Here we explore the idea that the explosion data can provide useful insights regarding the orientation of ubiquitin, a eukaryotic regulatory protein. Through two series of molecular dynamics simulations totaling 588 unique explosions, we found that a majority of the carbon atoms prevalent in ubiquitin are directionally limited in their respective escape paths. As such we conclude it to be theoretically possible to orient a sample with known structure based on its explosion pattern. Working with an unknown sample, we suggest these discoveries could be applicable in tandem with X-ray diffraction data to optimize image assembly.

Röntgenlicht-Freie-Elektronen-Laser (XFEL) schaffen neue Möglichkeiten für die molekulare Strukturbestimmung in Einzelmolekülexperimenten. In dieser Arbeit stelle ich zwei alternative bayessche Verfahren vor, das Orientational Bayes und das Structural Bayes Verfahren, die das Extrahieren der Strukturinformationen aus dünn besetzten und verrauschten Streuungsbildern ermöglichen. Im ersten Verfahren wird ein "Seed"-Modell verwendet, um die zugrunde liegende molekulare Orientierung für jedes aufgezeichnete Streuungsbild separat zu bestimmen. Eine verbesserte molekulare Transformation der bestrahlten Moleküle wird durch Ausrichten und Mitteln dieser Bilder im dreidimensionalen reziproken Raum erhalten. Im Structural Bayes Verfahren wird ein Realraum-Strukturmodell optimiert, sodass es am besten zum gesamten Streuungsbildersatz passt. Auf diese Weise wird ermöglicht, zwischen verschiedenen Strukturmodellen zu unterscheiden. Ich habe die Auflösung bei der Abbildung einzelner Moleküle mit unterschiedlichen Massen für verschiedene XFEL Strahlintensitäten abgeschätzt. Die Ergebnisse zeigen, dass die erreichbare strukturelle Auflösung mit der Molekülmasse wie M^{-1/ 6} steigt. Laut dieser Skalierung ist hierbei, im Gegensatz zur traditionellen Röntgenkristallographie, die hochaufgelöste Strukturbestimmung kleiner Einzelmoleküle, im Vergleich zu großen Molekülen, schwieriger. Als Machbarkeitsnachweis des Orientational Bayes Verfahrens wurde beispielhaft die Elektronendichte eines Glutathion-Moleküls aus 20.000 synthetischen Streuungsbildern, mit durchschnittlich 82 aufgezeichneten elastisch gestreuten Photonen und bis zu 50% zusätzlichem Hintergrundrauschen pro Bild, berechnet. Um die Anwendbarkeit des Structural Bayes Verfahrens in einer de novo Strukturbestimmung zu testen, wurde zudem die Struktur des Glutathion-Moleküls in einer Monte Carlo-Verfeinerungs-Simulation gelöst, für die zufällige Aminosäure-Konformationen als Ausgangsmaterial verwendet wurden. Um zusätzlich zu prüfen, ob mehrere Längenskalen umfassende Strukturänderungen in einem komplexen Molekül unter Verwendung des Structural Bayes Verfahrens rückverfolgbar sind, wurden Konformationsänderungen von drei Immunglobulin-Domänen eines Titin-Moleküls sowie der tRNA-Translokationsvorgang im Ribosom untersucht. Die Ergebnisse zeigen, dass es möglich ist sowohl zwischen unterschiedlichen molekularen Konformationen zu unterscheiden als auch kleinere strukturelle Änderungen, die mit der tRNA-Translokation assoziiert sind, zu erkennen. Insgesamt betrachtet deuten die Ergebnisse dieser Arbeit darauf hin, dass sich mithilfe der beiden hier vorgestellten bayesschen Verfahren die Struktur einzelner Moleküle mit atomarer Auflösung von dünn besetzten und verrauschten Röntgenstreuungsbildern aus XFEL-Einzelmolekülexperimenten für ein breites Spektrum von Molekülmassen bestimmen lässt.

During the last years we have seen the birth of free-electron lasers, a new type of light source ten billion times brighter than syncrotrons and able to produce pulses only a few femtoseconds long. One of the main motivations for building these multi-million dollar machines was the prospect of imaging biological samples such as proteins and viruses in 3D without the need for crystallization or staining. This thesis contains some of the first biological results from free-electron lasers. These results include 2D images, both of whole cells and of the giant mimivirus and also con- tains a 3D density map of the mimivirus assembled from diffraction patterns from many virus particles. These are important proof-of-concept experiments but they also mark the point where free-electron lasers start to produce biologically relevant results. The most noteworthy of these results is the unexpectedly non-uniform density distribution of the internals of the mimivirus. We also present Hawk, the only open-source software toolkit for analysing single particle diffraction data. The Uppsala-developed program suite supports a wide range fo algorithms and takes advantage of Graphics Processing Units which makes it very computationally efficient. Last, the problem introduced by structural variability in samples is discussed. This includes a description of the problem and how it can be overcome, and also how it could be turned into an advantage that allows us to image samples in all of their conformational states.

abstract: Phase problem has been long-standing in x-ray diffractive imaging. It is originated from the fact that only the amplitude of the scattered wave can be recorded by the detector, losing the phase information. The measurement of amplitude alone is insufficient to solve the structure. Therefore, phase retrieval is essential to structure determination with X-ray diffractive imaging. So far, many experimental as well as algorithmic approaches have been developed to address the phase problem. The experimental phasing methods, such as MAD, SAD etc, exploit the phase relation in vector space. They usually demand a lot of efforts to prepare the samples and require much more data. On the other hand, iterative phasing algorithms make use of the prior knowledge and various constraints in real and reciprocal space. In this thesis, new approaches to the problem of direct digital phasing of X-ray diffraction patterns from two-dimensional organic crystals were presented. The phase problem for Bragg diffraction from two-dimensional (2D) crystalline monolayer in transmission may be solved by imposing a compact support that sets the density to zero outside the monolayer. By iterating between the measured stucture factor magnitudes along reciprocal space rods (starting with random phases) and a density of the correct sign, the complex scattered amplitudes may be found (J. Struct Biol 144, 209 (2003)). However this one-dimensional support function fails to link the rod phases correctly unless a low-resolution real-space map is also available. Minimum prior information required for successful three-dimensional (3D) structure retrieval from a 2D crystal XFEL diffraction dataset were investigated, when using the HIO algorithm. This method provides an alternative way to phase 2D crystal dataset, with less dependence on the high quality model used in the molecular replacement method. / Dissertation/Thesis / Doctoral Dissertation Physics 2016

All across physics research, incoherent and coherent light sources are extensively utilized. Especially highly brilliant X-ray sources such as third generation synchrotrons or free-electron lasers have become an invaluable tool enabling experimental techniques that are unique to these kinds of light sources. But these sources have developed to large scale facilities and a demand in compact laboratory scale sources providing radiation of similar quality arises nowadays. This thesis focuses on Traveling-Wave Thomson-Scattering (TWTS) which allows for the realization of ultra-compact, inherently synchronized and highly brilliant light sources. The TWTS geometry provides optical undulators, through which electrons pass and thereby emit radiation, with hundreds to thousands of undulator periods by utilizing pulse-front tilted lasers pulses from high peak-power laser systems. TWTS can realize incoherent radiation sources with orders of magnitude higher photon yield than established head-on Thomson sources. Moreover, optical free-electron lasers (OFELs) can be realized with TWTS if state-of-the-art technology in electron accelerators and laser systems is utilized. Tilting the laser pulse front with respect to the wavefront by half of this interaction angle optimizes electron and laser pulse overlap by compensating the spatial offset between electrons and the laser pulse-front at the beginning of the interaction when the electrons are far from the laser pulse axis. The laser pulse-front tilt ensures continuous overlap between electrons and laser pulse while the electrons cross the laser pulse cross-sectional area. Thus the interaction distance can be controlled in TWTS by the laser pulse width rather than laser pulse duration. Utilizing wide, petawatt class laser pulses allows realizing thousands of optical undulator periods. This thesis will show that TWTS OFELs emitting ultraviolet radiation are realizable today with existing technology for electron accelerators and laser systems. The requirements on electron bunch and laser pulse quality of these ultraviolet TWTS OFELs are discussed in detail as well as the corresponding requirements of TWTS OFELs emitting in the soft and hard X-ray range. These requirements are derived from scaling laws which stem from a self-consistent analytic description of the electron bunch and radiation field dynamics in TWTS OFELs presented within this thesis. It is shown that these dynamics in TWTS OFELs are qualitatively equivalent to the electron bunch and radiation field dynamics of standard free-electron lasers which analytically proves the applicability of TWTS for the realization of an optical free-electron laser. Furthermore, experimental setup strategies to generate the pulse-front tilted TWTS laser pulses are presented and designs of experimental setups for the above examples are discussed. The presented setup strategies provide dispersion compensation, required due to angular dispersion of the laser pulse, which is especially relevant when building compact, high-yield hard X-ray TWTS sources in large interaction angle setups. An example of such an enhanced Thomson source by TWTS, which provides orders of magnitude higher spectral photon density than a comparable head-on interaction geometry, is presented, too

Les récents progrès en termes de techniques d’accélération par interaction Laser Plasma (LPA) permettent aujourd’hui de générer de forts gradients accélérateurs (GV.m⁻¹); cependant, les faisceaux d’électrons ainsi produits présentent encore une grande dispersion énergie (%) et une divergence élevée (mrad). Le projet COXINEL (ERC Advanced Grant 350014, PI. M.E. Couprie), vise à qualifier, en remplacement d’un accélérateur conventionnel, un accélérateur Laser Plasma, dans le but d’une application de Laser à Électrons Libres. Pour atteindre les propriétés requises, le faisceau d’électrons doit être manipulé à l’aide d’une ligne de transport. Cette ligne est constituée d’un premier triplet de quadrupôles à aimants permanents de gradient variable qui focalise le faisceau et permet la maîtrise de la divergence initiale. Une chicane électromagnétique réduit ensuite la dispersion en énergie par tranche en allongeant longitudinalement le faisceau. Une gamme d’énergie restreinte peut être ensuite sélectionnée via l’insertion d’une fente dans la chicane. Enfin, un quadruplet de quadrupôles électromagnétiques fournit la focalisation finale dans un onduleur. Le travail de thèse porte sur l’étude du transport des faisceaux d’électrons produit par LPA le long de cette ligne. Différents régimes de production d’électrons ont été utilisés : injection par ionisation, cellule de gaz. La maîtrise du transport a été obtenue à l’aide d’une nouvelle méthode d’alignement et de compensation de dérive de pointé initial des électrons en réglant de manière indépendante la position et la dispersion du faisceau à différents endroits de la ligne. Un réglage fin de l’énergie transportée a été effectué en ajustant le gradient des quadrupôles. Les faisceaux produits ont été transportés le long de la ligne et caractérisés en termes de distribution transverse, d’émittance et d’énergie. Les résultats expérimentaux ont ensuite été comparés avec succès aux simulations numériques. Ce travail ouvre la voie à l’observation de rayonnement de l’onduleur, étape préliminaire à une amplification Laser à Électrons Libres. / Recent advances in Laser Plasma Acceleration techniques (LPA) are now able to generate strong accelerating gradients (GV.m⁻¹); however the produced electron beam thus still presents a large energy spread (%) and a large divergence (mrad). The COXINEL project (ERC Advanced Grant 350014, PI. M.E. Couprie), aims at qualifying, in replacement of a conventional accelerator, a Laser Plasma Accelerator, for a Free Electrons Laser application. To achieve the required properties, the electron beam must be manipulated using a transport line. This line consists in a first triplet of permanent magnets quadrupoles of variable gradient which focuses the beam and allows for the control of the initial divergence. An electromagnetic chicane then reduces the slice energy spread by lengthening the beam longitudinally. A restricted energy range can then be selected by inserting a slit inside the chicane. Finally, a quadruple of electromagnetic quadrupoles provides the final focus in an undulator. The thesis deals on the study of electron beam transport produced by LPA along this line. Different electron production regimes have been used: ionization injection, gas cell. The transport was controlled using a new alignment and pointing compensation method for the initial electron beam by adjusting independently the beam position and dispersion at different location on the line. A fine adjustment of the transported energy was carried out by adjusting the quadrupole gradient. The produced beam was transported along the line and was characterized in terms of transverse distribution, emittance and energy. Experimental results were then successfully compared with numerical simulations. This work paves the way for the observation of undulator radiation, a preliminary step before Free Electron Laser amplification.

All across physics research, incoherent and coherent light sources are extensively utilized. Especially highly brilliant X-ray sources such as third generation synchrotrons or free-electron lasers have become an invaluable tool enabling experimental techniques that are unique to these kinds of light sources. But these sources have developed to large scale facilities and a demand in compact laboratory scale sources providing radiation of similar quality arises nowadays. This thesis focuses on Traveling-Wave Thomson-Scattering (TWTS) which allows for the realization of ultra-compact, inherently synchronized and highly brilliant light sources. The TWTS geometry provides optical undulators, through which electrons pass and thereby emit radiation, with hundreds to thousands of undulator periods by utilizing pulse-front tilted lasers pulses from high peak-power laser systems. TWTS can realize incoherent radiation sources with orders of magnitude higher photon yield than established head-on Thomson sources. Moreover, optical free-electron lasers (OFELs) can be realized with TWTS if state-of-the-art technology in electron accelerators and laser systems is utilized. Tilting the laser pulse front with respect to the wavefront by half of this interaction angle optimizes electron and laser pulse overlap by compensating the spatial offset between electrons and the laser pulse-front at the beginning of the interaction when the electrons are far from the laser pulse axis. The laser pulse-front tilt ensures continuous overlap between electrons and laser pulse while the electrons cross the laser pulse cross-sectional area. Thus the interaction distance can be controlled in TWTS by the laser pulse width rather than laser pulse duration. Utilizing wide, petawatt class laser pulses allows realizing thousands of optical undulator periods. This thesis will show that TWTS OFELs emitting ultraviolet radiation are realizable today with existing technology for electron accelerators and laser systems. The requirements on electron bunch and laser pulse quality of these ultraviolet TWTS OFELs are discussed in detail as well as the corresponding requirements of TWTS OFELs emitting in the soft and hard X-ray range. These requirements are derived from scaling laws which stem from a self-consistent analytic description of the electron bunch and radiation field dynamics in TWTS OFELs presented within this thesis. It is shown that these dynamics in TWTS OFELs are qualitatively equivalent to the electron bunch and radiation field dynamics of standard free-electron lasers which analytically proves the applicability of TWTS for the realization of an optical free-electron laser. Furthermore, experimental setup strategies to generate the pulse-front tilted TWTS laser pulses are presented and designs of experimental setups for the above examples are discussed. The presented setup strategies provide dispersion compensation, required due to angular dispersion of the laser pulse, which is especially relevant when building compact, high-yield hard X-ray TWTS sources in large interaction angle setups. An example of such an enhanced Thomson source by TWTS, which provides orders of magnitude higher spectral photon density than a comparable head-on interaction geometry, is presented, too

Les lasers à électrons libres (LEL) X sont aujourd'hui des sources lumineuses cohérentes et intenses utilisées pour des investigations multidisciplinaires de la matière. Un nouveau schéma d'accélération, l'accélérateur laser plasma (LPA), est maintenant capable de produire une accélération de quelques GeV/cm, bien supérieure à celle des linacs radiofréquence. Ce travail de thèse a été mené dans le cadre des programmes de R&D du projet LUNEX5 (laser à électrons libres utilisant un nouvel accélérateur pour l’exploitation du rayonnement X de 5e génération) de démonstrateur LEL avancé et compact avec applications utilisatrices pilotes. Il comprend un linac supraconducteur de 400 MeV de haute cadence (10 kHz) pour l’étude de schémas LEL avancés, et LPA pour sa qualification par une application LEL. La ligne LEL utilise une configuration d’injection avancée dans la plage spectrale 40-4 nm par génération d’harmoniques à gain élevé (HGHG) et schéma d’écho (EEHG) avec des onduleurs compacts cryogéniques à champ élevé de courte période courte. L'étude de solutions adaptées aux applications LEL compactes et avancées est donc examinée. Un premier aspect concerne la réduction du milieu de gain du LEL (électrons dans l'onduleur), le raccourcissement de la période se faisant au détriment du champ magnétique. Les onduleurs cryogéniques compacts à base d'aimants permanents cryogéniques (CPMU), dans lesquels les performances de l'aimant sont améliorées à la température cryogénique sont étudiés. Une deuxième partie du travail développée dans le cadre l’expérience de R&D COXINEL visant à démontrer l’amplification LEL à l’aide d’un LPA. La ligne permet de manipuler les propriétés des faisceaux d’électrons produits (dispersion en énergie, divergence, variation de pointé) avant d’être utilisées pour des applications de sources lumineuses. Le faisceau d'électrons généré est très divergent et nécessite une bonne manipulation juste après la source avec des quadrupôles forts placés immédiatement après la génération d'électrons. Ainsi, des quadrupôles innovants à aimants permanents de gradient élevé réglable appelés «QUAPEVA», sont développés. Ils sont optimisés avec le code RADIA et caractérisées avec trois mesures magnétiques. Un gradient de 200 T/m avec une variabilité de 50 % est obtenu tout en maintenant une excursion du centre magnétique réduite à ± 10 µm, qui a permis un alignement par compensation de pointé du faisceau dans COXINEL grâce au centre magnétique variable des systèmes, avec un faisceau bien focalisé sans dispersion. Les QUAPEVA constituent des systèmes originaux dans le paysage des quadrupôles à de gradient élevé et variable développés jusqu'à présent. Une troisième partie des travaux concerne l’observation du rayonnement d’onduleur monochromatique ajustable sur la ligne COXINEL. Le faisceau d'électrons d'énergie de 170 MeV est transporté et focalisé dans un CPMU de 2 m et de période de 18 mm émettant à 200 nm. Le flux spectral est caractérisé à l'aide d'un spectromètre UV et le flux angulaire mesuré par une caméra CCD. La longueur d'onde est accordée avec l’entrefer. Les distributions spatio-spectrales mesurées en forme de lune du rayonnement de l'onduleur sont bien reproduites par les simulations de rayonnement utilisant les distributions d’électrons mesurées et transportées le long de la ligne. Elles permettent aussi de renseigner sur la qualité du faisceau d’électrons, de son transport et d'en estimer les paramètres tels que la dispersion en énergie et la divergence. Le dernier aspect du travail est lié à la comparaison entre la génération des harmoniques en gain élevé et le schéma d’écho, dans le cadre de ma participation à une expérience réalisée à FERMI @ ELETTRA. Nous avons pu démontrer un LEL de type écho à 5,9 nm, avec spectres plus étroits et une meilleure reproductibilité que le schéma HGHG à deux étages. Cette thèse constitue un pas en avant vers les lasers à électrons libres compacts et avancés. / X-ray Free Electron Lasers (FEL) are nowadays unique intense coherent fs light sources used for multi-disciplinary investigations of matter. A new acceleration scheme such as Laser Plasma Accelerator (LPA) is now capable of producing an accelerating gradient of few GeV/cm far superior to that of conventional RF linacs. This PhD work has been conducted in the framework of R&D programs of the LUNEX5 (free electron Laser Using a New accelerator for the Exploitation of X-ray radiation of 5th generation) project of advanced and compact Free Electron laser demonstrator with pilot user applications. It comprises a 400 MeV superconducting linac for studies of advanced FEL schemes, high repetition rate operation (10 kHz), multi-FEL lines, a Laser Wake Field Accelerator (LWFA) for its qualification by a FEL application. The FEL lines comports enables advanced seeding in the 40-4 nm spectral range using high gain harmonic generation (HGHG) and echo-enabled harmonic generation (EEHG) with compact short period high field cryogenic undulators. The study of compact devices suitable for compact FEL applications is thus examined. One first aspect concerns the reduction of the Free Electron Laser gain medium (electrons in undulator) where shortening of the period is on the expense of the magnetic field leading to an intensity reduction at high harmonics. Compact cryogenic permanent magnet based undulators (CPMUs), where the magnet performance is increased at cryogenic temperature making them suitable for compact applications, are studied. Three CPMUs of period 18 mm have been built: two are installed at SOLEIL storage ring and one at COXINEL experiment. A second part of the work is developed in the frame of the R&D programs is the COXINEL experiment with an aim at demonstrating FEL amplification using an LPA source. The line enables to manipulate the properties of the produced electron beams (as energy spread, divergence, induced dispersion due) before being used for light source applications. The electron beam generated is highly divergent and requires a good handling at an early stage with strong quadrupoles, to be installed immediately after the electron generation source. Hence, the development of the so-called QUAPEVAs, innovative permanent magnet quadrupoles with high tunable gradient, is presented. The QUAPEVAs are optimized with RADIA code and characterized with three magnetic measurements. High tunable gradient is achieved while maintaining a rather good magnetic center excursion that allowed for beam pointing alignment compensation at COXINEL, where the beam is well-focused with zero dispersion at any location along the line. The QUAPEVAs constitute original systems in the landscape of variable high gradient quadrupoles developed so far. A third part of the work concerns the observation of tunable monochromatic undulator radiation on the COXINEL line. The electron beam of energy of 170 MeV is transported and focused in a 2-m long CPMU with a period of 18 mm emitting radiation light at 200 nm. The spectral flux is characterized using a UV spectrometer and the angular flux is captured by a CCD camera. The wavelength is tuned with the undulator gap variation. The spatio-spectral moon shape type pattern of the undulator radiation provided an insight on the electron beam quality and its transport enabling the estimation of the electron beam parameters such as energy spread and divergence. The final aspect of the work is related to the comparison between the echo and high gain harmonic generation, in the frame of my participation to an experiment carried out at FERMI@ELETTRA. At FERMI, we have demonstrated a high gain lasing using EEHG at a wavelength of 5.9 nm where it showed a narrower spectra and better reproducibility compared to a two-stage HGHG. This PhD work constitutes a step forward towards advanced compact Free Electron Lasers.