The thesis deals with the development and characterization of new light sources, which are mandatory for applications in atomic and molecular spectroscopy, medical and biological imaging or industrial production. For that purpose, the employment of interactions of high intensity ultra-short laser pulses with gaseous media offers a rich variety of physical effects which can be exploited. The effects are characterized by a nonlinear dependency on the present light fields. Therefore, accurate modeling of the nonlinearities of the gas is crucial. In general, the nonlinearities are due to the electronic response of the gas atoms to the light field and one distinguishes between the response of bound and ionized electrons. The first part investigates laser pulse self compression, where the consideration of a purely bound electron response is sufficient. We apply an exotic setup with an negative Kerr nonlinearity in order to avoid spatial collapse of the beam on the cost of dealing with an highly dispersive nonlinearity. Analytical analysis and numerical simulations prove the possibility of laser pulse compression in such setups and reveals a new compression scheme, where the usually disturbing dispersion of the nonlinaerity is responsible for compression. Dealing with tera-Hertz generation by focusing an ionizing two-color laser pulse into gas, the second part exploits a medium nonlinearity caused by ionized electrons. We reveal in a mixed analytical and numerical analysis the underlying physical mechanism for THz generation: ionized electrons build up a current, which radiates. Thereby, the the two-color nature of the input laser is crucial for the emitted radiation to be in the tera-Hertz range. Combining this physical model with a pulse propagation equation allows us to achieve remarkable agreement with experimental measurements. Finally, the third part deals with nonlinearities from bound as well from ionized electrons on a fundamental level. We advance beyond phenomenological models for responses of bound and ionized electrons and quantum mechanically model the interaction of an ultra-short laser pulse with a gas. Already the simplest case of one dimensional hydrogen reveals basic features. For low intensities, the Kerr nonlinearity excellently describes the response of bound electrons. For increasing intensity, ionization becomes important and the response from ionized electrons is the governing one for high intensities. This quantum mechanical correct modeling allows us to explain saturation and change of sing of the nonlinear refractive index and to deduce suited approximate models for optical nonlinearities.

The thesis deals with the development and characterization of new light sources, which are mandatory for applications in atomic and molecular spectroscopy, medical and biological imaging or industrial production. For that purpose, the employment of interactions of high intensity ultra-short laser pulses with gaseous media offers a rich variety of physical effects which can be exploited. The effects are characterized by a nonlinear dependency on the present light fields. Therefore, accurate modeling of the nonlinearities of the gas is crucial. In general, the nonlinearities are due to the electronic response of the gas atoms to the light field and one distinguishes between the response of bound and ionized electrons. The first part investigates laser pulse self compression, where the consideration of a purely bound electron response is sufficient. We apply an exotic setup with an negative Kerr nonlinearity in order to avoid spatial collapse of the beam on the cost of dealing with an highly dispersive nonlinearity. Analytical analysis and numerical simulations prove the possibility of laser pulse compression in such setups and reveals a new compression scheme, where the usually disturbing dispersion of the nonlinaerity is responsible for compression. Dealing with tera-Hertz generation by focusing an ionizing two-color laser pulse into gas, the second part exploits a medium nonlinearity caused by ionized electrons. We reveal in a mixed analytical and numerical analysis the underlying physical mechanism for THz generation: ionized electrons build up a current, which radiates. Thereby, the the two-color nature of the input laser is crucial for the emitted radiation to be in the tera-Hertz range. Combining this physical model with a pulse propagation equation allows us to achieve remarkable agreement with experimental measurements. Finally, the third part deals with nonlinearities from bound as well from ionized electrons on a fundamental level. We advance beyond phenomenological models for responses of bound and ionized electrons and quantum mechanically model the interaction of an ultra-short laser pulse with a gas. Already the simplest case of one dimensional hydrogen reveals basic features. For low intensities, the Kerr nonlinearity excellently describes the response of bound electrons. For increasing intensity, ionization becomes important and the response from ionized electrons is the governing one for high intensities. This quantum mechanical correct modeling allows us to explain saturation and change of sing of the nonlinear refractive index and to deduce suited approximate models for optical nonlinearities.

Das Verständnis der inneren Vorgänge in der Materie, einschließlich des komplizierten Tanzes von Elektronen, Atomen und Molekülen, hat Forscher schon lange fasziniert. Elektronen werden seit der Erfindung des Elektronenmikroskops zur Untersuchung von Materie eingesetzt, aber erst in jüngster Zeit haben Fortschritte in der Elektronenquellen- und Beschleunigertechnologie die Erzeugung von Elektronenstrahlen mit hoher Helligkeit und Energien im Megaelektronenvoltbereich ermöglicht. Diese Entwicklungen versprechen die Beobachtung des Verhaltens von Materie auf atomarer Ebene. Die Forschung in dieser Dissertation konzentriert sich auf die Bereitstellung von Elektronenstrahlen im Megaelektronenvoltbereich, die für die Untersuchung von Materialien geeignet sind. Angesichts der Herausforderungen, die sich aus den für solche Experimente erforderlichen niedrigen Intensitäten und geringen Emittanzen ergeben, werden die notwendigen Modifikationen an der Strahllinie des SRF-Photoinjektors untersucht. Anschließend wird eine experimentelle Kampagne durchgeführt, um spezielle Strahldiagnosetechniken zur Echtzeitüberwachung des Strahls zu testen. Darüber hinaus werden die Fähigkeiten des Beschleunigers zur Durchführung zeitaufgelöster Elektronenstreuexperimente mit Auflösungen auf atomarer Zeitskala untersucht. Unsere Ergebnisse zeigen das Potenzial des SRF-Photoinjektors und ähnlicher Beschleuniger, ultraschnelle Elektronenstreuexperimente mit beispielloser zeitlicher Auflösung durchzuführen. Darüber hinaus können diese Beschleuniger genutzt werden, um lokalisierte Prozesse mit räumlichen Auflösungen von über 10 Nanometern zu beobachten, indem ein geeignetes Design der Elektronenoptik verwendet wird, für das ein innovativer Ansatz vorgeschlagen wird. Durch die Untersuchung der Grenzen der aktuellen Beschleunigertechnologie bei der Durchführung von Materieuntersuchungsexperimenten mit relativistischen Elektronen werden die Grenzen dieses Feldes in neue Richtungen verschoben. / Understanding the inner workings of matter, including the intricate dance of electrons, atoms, and molecules, has long captivated researchers. Electrons have been employed to probe matter since the advent of the electron microscope, but it has not been until recently that advancements in electron source and accelerator technology have enabled the production of high-brightness electron beams with megaelectronvolt energies. These developments hold promise for enabling the observation of matter’s behaviors at atomic scales. The research in this dissertation focuses on delivering megaelectronvolt electron beams suitable for the investigation of materials. Considering the challenges posed by the low intensities and small emittances required for such experiments, the necessary modifications to the SRF Photoinjector's beamline are studied. An experimental campaign is then conducted to test dedicated beam diagnostic techniques for real-time monitoring of the beam. Furthermore, the accelerator’s capabilities for conducting time-resolved electron scattering experiments with resolutions at atomic temporal scales are investigated. Our findings reveal the potential of the SRF Photoinjector and similar accelerators to perform ultrafast electron scattering experiments with unprecedented temporal resolutions. Additionally, these accelerators can be utilized to observe localized processes with spatial resolutions surpassing 10 nanometers by using an appropriate design of electron optics, for which an innovative approach is proposed. By studying the limitations of current accelerator technology in conducting matter-probing experiments with relativistic electrons, the boundaries of this field are pushed toward new frontiers.

Die vorliegende Arbeit beschäftigt sich mit dem Konzept der radial nicht-oszillierenden, zeitlich stabilen ultrakurzen Bessel ähnlichen Strahlen oder "Nadelstrahlen" ("needle beams"), die zu einer Klasse von optischen hochlokalisierten Wellenpaketen generalisiert werden. Hierbei wird die Theorie über das räumlich-zeitlichen Ausbreitungsverhaltens von nicht auseinanderdriftenden Nadelstrahlen mit Pulsdauern von kleiner als 10 fs näher diskutiert. Dies wird durch eine systematische Darstellung der Methoden zur Generierung und Detektierung von lokalisierten Wellen komplettiert, die ein optischen Drehmoment tragen. Für die Erzeugung von HLWs kommen räumliche Lichtmodulatoren zum Einsatz, die ein flexibles Zuschneiden von Wellenpaketen mit der Dauer weniger Zyklen des EM-Feldes erlauben. Es wird gezeigt, dass solche optischen Pulse sich über beträchtliche Entfernungen ausbreiten, ohne dass sich dabei signifikant der Strahldurchmesser vergrößert oder der Puls zeitlich verbreitert. In variabler Weise werden verschiedene geometrische (z.B. ringförmige) Lichtverteilungen erzeugt. Anwendungspotential findet sich insbesondere in den Techniken der räumlichen Pulsformung und Diagnostik. Als besonders wichtiger Ansatz ist der Zeit-Wellenfront-Sensor zu erwähnen, welcher die nichtlineare, mehrkanalige Autokorrelation, die Wellenfrontdetektion mittels nichtdiffraktiver Teilstrahlen nach dem Shack-Hartmann-Prinzip und eine adaptive Funktionalität miteinander vorteilhaft verbindet. Das enorme Potential solcher Ansätze wird durch die hohe Genauigkeit orts-, winkel- und zeitabhängiger Rekonstruktionen der Wellenpakete nachgewiesen. Darüber hinaus ermöglicht das räumliche Kodieren und anschließende Verfolgen der Teilstrahlen eine wesentliche Verbesserung der Identifikation relevanter Parameter von Verteilungsfunktionen. Schließlich werden erste Schritte zur experimentellen Generation von optischen "light bullets" mit ganzzahligen und fraktalen orbitalen Drehmomenten präsentiert. / This thesis deals with the concept of radially non-oscillating, temporally stable ultrashort-pulsed Bessel-like beams or "needle pulses", which are an example of a highly localized wave packet (HLW). HLWs are the closest approximation of linear-optical light bullets and provide specific benefits compared to conventional Gaussian-like light bullets. The spatio-temporally nonspreading propagation behavior of few-cycle needle beams of less than 10 fs duration will be theoretically discussed in detail. An overview of the generation and detection of localized waves carrying an orbital angular momentum is also given. High fidelity spatial light modulators are used for the generation of HLWs. The flexible tailoring of few-cycle wave packets at near-infrared wavelengths is reported. It is shown that such pulses propagate over a huge depth of focus, neither significantly changing their spot size or nor the pulse duration. Variable geometrical distributions like circular disks, rings, or bars of light are shaped and exploited as building blocks for structures of higher complexity. Another section of the thesis emphasizes the numerous potential applications of related techniques for an optimized two-dimensional spatial pulse shaping and diagnostics (reduce ambiguities) based on localized waves. As a particularly important example, time-wavefront sensing is used to combine nonlinear multichannel autocorrelation with Shack-Hartmann wavefront sensing by means of localized sub-beams and adaptive functionality. The capabilities of such devices are illustrated by the results of angular and temporal mapping of few-cycle wave packets. Moreover, spatial encoding and subsequent tracking of individual sub-beams, even at incident angles of up to 50°, enables to significantly improve the spot recognition. Finally, first steps towards the generation of optical light bullets carrying integer or non-integer orbital angular momenta are presented.