Doctor of Philosophy / Department of Physics / Daniel Rolles / Modern laser sources can produce bursts of light that surpass even the fastest molecular vibrations. With durations this short even moderate pulse energies generate peak powers exceeding the average power output of the entire globe. When focused, this can result in an ultrafast electric field greater than the Coulomb potential that binds electrons to nuclei. This strong electric field strips electrons away from atoms in a process known as strong-field ionization. The first experimental realization of photoionization with intense laser pulses occurred only a few years after the invention of the laser. Yet, despite decades of intensive investigation, open questions remain. At the same time, the knowledge gained has led to the creation of multiple exciting fields such as attoscience, femtochemistry, and ultrafast nano-photonics. In this thesis I present my work to advance the fundamental understanding of intense, ultrafast light-matter interactions as well as efforts to expand the technological capabilities of ultrafast light sources and measurement techniques. This includes the photoionization pro- cess of atoms and nanoparticles subject to intense, mid-infrared laser fields. The resulting photoelectron emission is measured, with high precision, in a velocity map imaging spec- trometer. Other parts of this thesis detail my work on the generation and characterization of non-Gaussian optical pulses. Femtosecond Bessel beams are used to drive and study high harmonic generation with the ultimate goal of creating a compact, high-flux XUV source. Further studies include few-cycle pulses and the carrier-envelope phase, specifically methods of locking and tagging the carrier-envelope phase. A single-shot, all optical tagging method is developed and directly compared to the standard tagging method, the carrier-envelope phase meter. Finally, both experimental and computational studies are presented investigating the ultrafast thermal response cycle of nanowires undergoing femtosecond heating.

One of the most promising devices to provide accurate measurement of the longitudinal bunch profile at the tens of femtosecond level is based on electro-optic techniques. In this thesis, a bunch profile monitor, based on electro-optic spectral decoding (EOSD), is currently developed for the CLIC Test Facility 3 at CERN. The monitor is optimised for bunch lengths over 3.5 ps with effective window of 16 ps, and sub-picosecond resolution. The measurement results from the EO monitor are compared with measurements by coherent transition radiation on a streak camera. The measurement on bunch charge dependence is studied. Timing resolution of the bunch profile monitor is studied in both theory and numerical calculation. This thesis summarises a frequency analysis approach of electro-optic effect based on $\chi^{(2)}$ frequency mixing process. From the theory analysed in frequency domain, a non-crossed polarization measurement includes all three of the probe laser background term, the linear term to Coulomb field and the quadratic term to Coulomb field. Three methods are induced based on this frequency analysis result to retrieve Coulomb field value which is emitted from electron beam. The measured 1.3 MV/m field strength agrees with calculation result. An experiment is designed to study the role of incident beam sizes and non-collinear incident beams in EO technique. Due to the phase matching process, the non-collinear angle of the incident beams induces a frequency dependent angular chirp in the beams emitted after the EO crystal. This frequency offset may lead to frequency loss in fibre coupling, and thus lead to bunch length broadening in a measurement for short electron bunch.

This publication-based thesis represents a contribution to the active research field of ultrafast structural dynamics in laser-excited nanostructures. The investigation of such dynamics is mandatory for the understanding of the various physical processes on microscopic scales in complex materials which have great potentials for advances in many technological applications. I theoretically and experimentally examine the coherent, incoherent and anharmonic lattice dynamics of epitaxial metal-insulator heterostructures on timescales ranging from femtoseconds up to nanoseconds. To infer information on the transient dynamics in the photoexcited crystal lattices experimental techniques using ultrashort optical and x-ray pulses are employed. The experimental setups include table-top sources as well as large-scale facilities such as synchrotron sources. At the core of my work lies the development of a linear-chain model to simulate and analyze the photoexcited atomic-scale dynamics. The calculated strain fields are then used to simulate the optical and x-ray response of the considered thin films and multilayers in order to relate the experimental signatures to particular structural processes. This way one obtains insight into the rich lattice dynamics exhibiting coherent transport of vibrational energy from local excitations via delocalized phonon modes of the samples. The complex deformations in tailored multilayers are identified to give rise to highly nonlinear x-ray diffraction responses due to transient interference effects. The understanding of such effects and the ability to precisely calculate those are exploited for the design of novel ultrafast x-ray optics. In particular, I present several Phonon Bragg Switch concepts to efficiently generate ultrashort x-ray pulses for time-resolved structural investigations. By extension of the numerical models to include incoherent phonon propagation and anharmonic lattice potentials I present a new view on the fundamental research topics of nanoscale thermal transport and anharmonic phonon-phonon interactions such as nonlinear sound propagation and phonon damping. The former issue is exemplified by the time-resolved heat conduction from thin SrRuO3 films into a SrTiO3 substrate which exhibits an unexpectedly slow heat conductivity. Furthermore, I discuss various experiments which can be well reproduced by the versatile numerical models and thus evidence strong lattice anharmonicities in the perovskite oxide SrTiO3. The thesis also presents several advances of experimental techniques such as time-resolved phonon spectroscopy with optical and x-ray photons as well as concepts for the implementation of x-ray diffraction setups at standard synchrotron beamlines with largely improved time-resolution for investigations of ultrafast structural processes. This work forms the basis for ongoing research topics in complex oxide materials including electronic correlations and phase transitions related to the elastic, magnetic and polarization degrees of freedom. / Diese publikationsbasierte Dissertation ist ein Beitrag zu dem aktuellen Forschungsgebiet der ultraschnellen Strukturdynamik in laserangeregten Nanostrukturen. Die Erforschung solcher Vorgänge ist unabdingbar für ein Verständnis der vielseitigen physikalischen Prozesse auf mikroskopischen Längenskalen in komplexen Materialien, welche enorme Weiterentwicklungen für technologische Anwendungen versprechen. Meine theoretischen und experimentellen Untersuchungen betrachten kohärente, inkohärente und anharmonische Gitterdynamiken in epitaktischen Metal-Isolator-Heterostrukturen auf Zeitskalen von Femtosekunden bis Nanosekunden. Um Einsichten in solche transienten Prozesse in laserangeregten Kristallen zu erhalten, werden experimentelle Techniken herangezogen, die ultrakurze Pulse von sichtbarem Licht und Röntgenstrahlung verwenden. Ein zentraler Bestandteil meiner Arbeit ist die Entwicklung eines Linearkettenmodells zur Simulation und Analyse der laserinitiierten Atombewegungen. Die damit errechneten Verzerrungsfelder werden anschließend verwendet, um die Änderung der optischen und Röntgeneigenschaften der betrachteten Dünnfilm- und Vielschichtsysteme zu simulieren. Diese Rechnungen werden dann mit den experimentellen Daten verglichen, um die experimentellen Signaturen mit errechneten strukturellen Prozessen zu identifizieren. Dadurch erhält man Einsicht in die vielseitige Gitterdynamiken, was z.B. einen kohärenten Transport der Vibrationsenergie von lokal angeregten Bereichen durch delokalisierte Phononenmoden offenbart. Es wird gezeigt, dass die komplexen Deformationen in maßgeschneiderten Vielschichtsystemen hochgradig nichtlineare Röntgenbeugungseffekte auf Grund von transienten Interferenzerscheinungen verursachen. Das Verständnis dieser Prozesse und die Möglichkeit, diese präzise zu simulieren, werden dazu verwendet, neuartige ultraschnelle Röntgenoptiken zu entwerfen. Insbesondere erläutere ich mehrere Phonon-Bragg-Schalter-Konzepte für die effiziente Erzeugung ultrakurzer Röntgenpulse, die in zeitaufgelösten Strukturanalysen Anwendung finden. Auf Grund der Erweiterung der numerischen Modelle zur Beschreibung von inkohärenter Phononenausbreitung und anharmonischer Gitterpotentiale decken diese ebenfalls die aktuellen Themengebiete von Wärmetransport auf Nanoskalen und anharmonischer Phonon-Phonon-Wechselwirkung (z.B. nichtlineare Schallausbreitung und Phononendämpfung) ab. Die erstere Thematik wird am Beispiel der zeitaufgelösten Wärmeleitung von einem dünnen SrRuO3-Film in ein SrTiO3-Substrat behandelt, wobei ein unerwartet langsamer Wärmetransport zu Tage tritt. Außerdem diskutiere ich mehrere Experimente, die auf Grund der sehr guten Reproduzierbarkeit durch die numerischen Modelle starke Gitteranharmonizitäten in dem oxidischen Perowskit SrTiO3 bezeugen. Diese Dissertation erarbeitet zusätzlich verschiedene Weiterentwicklungen von experimentellen Methoden, wie z.B. die zeitaufgelöste Phononenspektroskopie mittels optischer Photonen und Röntgenphotonen, sowie Konzepte für die Umsetzung von Röntgenbeugungsexperimenten an Standard-Synchrotronquellen mit stark verbesserter Zeitauflösung für weitere Studien von ultraschnellen Strukturvorgängen.

The main theme covered in this thesis is experimentalstudies of quantum dynamics and coherent control in homonuclearalkali diatomic molecules by ultrafast laser spectroscopy iththe implementation of pump-probe techniques. A series of experiments have been performed on the Rb2molecules in a molecular beam as well as in a thermal oven. Thereal-time molecular quantum dynamics of the predissociatingelectronically excited D(3)1Πu state of Rb2, which couples to/intersects several otherneighbouring states, is investigated using wavepackets. Thepredissociation of the D state, explored by this wavepacketmethod, arises from two independent states, the (4)3Σu+and (1)3∆u, for which the second corresponds to a much fasterdecay channel above a sharp energy threshold around 430 nm. Thelifetime of the D state above the energy threshold is obtained,τ ≈ 5 ps, by measuring the decay time of thewavepacket in a thermal oven. Further experimentalinvestigation performed in a molecular beam together withquantum calculations of wavepacket dynamics on the D state haveexplored new probe channels of wavepacket evolution: theD′(3)1Σu+ channel, which exhibits vibrational motionin a shelf state and the (4)3Σu+ channel, where direct build-up of thewavefunction is observed due to its spin-orbit oupling to the Dstate. The real-time quantum dynamics of wavepackets confined totwo bound states, A1Σu+(0u+) and b3Πu(0u+), have been studied by experiment andcalculations. It is shown that these two states are fullycoupled by spin-orbit interaction, characterised by itsintermediate strength. The intermediate character of thedynamics is established by complicated wavepacket oscillationatterns and a value of 75 cm-1is estimated for the coupling strength at thestate crossing. The experiments on the Li2molecule are performed by coherent control ofrovibrational molecular wavepackets. First, the Deutsch-Jozsaalgorithm is experimentally demonstrated for three-qubitfunctions using a pure coherent superposition of Li2rovibrational eigenstates. The function’scharacter, either constant or balanced, is evaluated by firstimprinting the function, using a phase-tailored femtosecond(fs) pulse, on a coherent superposition of the molecularstates, and then projecting the superposition onto an ionicfinal state using a second fs pulse at a specific delay time.Furthermore, an amplitude-tailored fs pulse is used to exciteselected rovibrational eigenstates and collision induceddephasing of the wavepacket signal, due to Li2-Ar collisions, is studied experimentally. Theintensities of quantum beats decaying with the delay time aremeasured under various pressures and the collisional crosssections are calculated for each well-defined rovibrationalquantum beat, which set the upper limitsfor ure dephasingcross sections. <b>Keywords:</b>Ultrafast laser spectroscopy, pump-probetechnique, predissociation, wavepacket, pin-orbit interaction,coherent control, (pure) dephasing

X-ray lasers are creating unprecedented research opportunities in physics,chemistry and biology. The peak brightness of these lasers exceeds presentsynchrotrons by 1010, the coherence degeneracy parameters exceedsynchrotrons by 109, and the time resolution is 105 times better. In theduration of a single flash, the beam focused to a micron-sized spot has the samepower density as all the sunlight hitting the Earth, focused to a millimetresquare. Ultrafast coherent X-ray diffractive imaging (CXDI) with X-ray lasers exploitsthese unique properties of X-ray lasers to obtain high-resolution structures fornon-crystalline biological (and other) objects. In such an experiment, thesample is quickly vaporised, but not before sufficient scattered light can berecorded. The continuous diffraction pattern can then be phased and thestructure of a more or less undamaged sample recovered% (speed of light vs. speed of a shock wave).This thesis presents results from the first ultrafast X-ray diffractive imagingexperiments with linear accelerator-driven free-electron lasers and fromoptically-driven table-top X-ray lasers. It also explores the possibility ofinvestigating phase transitions in crystals by X-ray lasers. An important problem with ultrafast CXDI of small samples such as single proteinmolecules is that the signal from a single measurement will be small, requiringsignal enhancement by averaging over multiple equivalent samples. We present anumerical investigation of the problems, including the case where samplemolecules are not exactly identical, and propose tentative solutions. A new software package (Hawk) has been developed for data processing and imagereconstruction. Hawk is the first publicly available software package in thisarea, and it is released as an open source software with the aspiration offostering the development of this field.

The biological significance of photosynthesis is indisputable as it is necessary for nearly all life on earth. Photosynthesis provides chemical energy for plants, algae, and bacteria, while heterotrophic organisms rely on these species as their ultimate food source. The initial step in photosynthesis requires the absorption of sunlight to create electronic excitations. Light-harvesting proteins play the functional role of capturing solar radiation and transferring the resulting excitation to the reaction centers where it is used to carry out the chemical reactions of photosynthesis. Despite the wide variety of light-harvesting protein structures and arrangements, most light-harvesting proteins are able to utilize the captured solar energy for charge separation with near perfect quantum efficiency. This thesis will focus on understanding the energy transfer dynamics and photophysics of a specific subset of light-harvesting antennae known as phycobiliproteins. These proteins are extracted from cryptophyte algae and are investigated using steady-state and ultrafast spectroscopic techniques.

The biological significance of photosynthesis is indisputable as it is necessary for nearly all life on earth. Photosynthesis provides chemical energy for plants, algae, and bacteria, while heterotrophic organisms rely on these species as their ultimate food source. The initial step in photosynthesis requires the absorption of sunlight to create electronic excitations. Light-harvesting proteins play the functional role of capturing solar radiation and transferring the resulting excitation to the reaction centers where it is used to carry out the chemical reactions of photosynthesis. Despite the wide variety of light-harvesting protein structures and arrangements, most light-harvesting proteins are able to utilize the captured solar energy for charge separation with near perfect quantum efficiency. This thesis will focus on understanding the energy transfer dynamics and photophysics of a specific subset of light-harvesting antennae known as phycobiliproteins. These proteins are extracted from cryptophyte algae and are investigated using steady-state and ultrafast spectroscopic techniques.

The lateral spatial separation between the circular polarization components of a linearly polarized light beam impinging at off-normal incidence on an air-semiconductor interface is investigated experimentally and theoretically. This fundamental optical phenomenon is referred to as the Spin Hall effect of light (SHEL). An optical pump-probe technique is demonstrated to resolve in situ the nanometer size SHEL displacement of a beam transmitted inside an absorptive material. Three different types of optical interactions in silicon and GaAs demonstrate the technique’s general applicability. First, resonant ∼150 fs pump and probe pulses at λ = 820 nm resolve the SHEL displacement via free-carrier absorption in a 10 μm thick silicon sample. The measured SHEL displacements for a p-polarized probe beam are obtained between −10 to 150 nm as a function of the angle of incidence on the sample. Different angles of incidence are achieved by keeping a fixed angular separation between the pump and the probe beams while rotating the sample about the axis perpendicular to the plane of incidence. In another experiment, an optically thin (500 nm thick) GaAs sample allows one to use Pauli-blocking as an optical interaction to investigate the polarization and angular dependence of the SHEL in the probe beam. For such a polarization-dependent imaging technique, the SHEL displacement in the pump beam also contributes to the measured signal and is evaluated experimentally. A probe beam at normal incidence is used to measure a SHEL displacement of ∼180 nm in a transmitted p-polarized pump beam impinging on the sample with an angle of incidence of 55 degrees. Finally, two-photon absorption is used to resolve the SHEL in a (001) oriented 500 μm thick GaAs wafer using an optical source generating sub-bandgap radiation (λ = 1550 nm) with a pulse duration of 120 fs. Linearly p- and s- co-polarized pump and probe beams are also used to investigate the polarization dependence of the SHEL. All the experimental results obtained using these different optical interactions agree with the theory within the experimental error. Finally, analytical expressions of the shifts experienced by the circular components of a beam impinging at an interface between two optical media are also derived for an incident beam with an arbitrary spatial distribution.

An algorithm for extracting event information from a Coulomb Explosion Imaging (CEI) position sensitive detector (PSD) is developed and compared with previously employed schemes. The PSD is calibrated using a newly designed grid overlay and validates the quality of the described algorithm. Precision calculations are performed to determine how best the CEI apparatus at The University of Waterloo can be improved. An algorithm for optimizing coincidence measurements of polyatomic molecules in CEI experiments is developed. Predictions of improved efficiency based on this algorithm are performed and compared with experiments using a triatomic molecule. Analysis of an OCS targeted CEI experiment using highly charged Argon ions to initiate ionization is performed. The resulting measurements are presented using a variety of visualization tools to reveal asynchronous and sequential fragmentation channels of OCS3+.

The lateral spatial separation between the circular polarization components of a linearly polarized light beam impinging at off-normal incidence on an air-semiconductor interface is investigated experimentally and theoretically. This fundamental optical phenomenon is referred to as the Spin Hall effect of light (SHEL). An optical pump-probe technique is demonstrated to resolve in situ the nanometer size SHEL displacement of a beam transmitted inside an absorptive material. Three different types of optical interactions in silicon and GaAs demonstrate the technique’s general applicability. First, resonant ∼150 fs pump and probe pulses at λ = 820 nm resolve the SHEL displacement via free-carrier absorption in a 10 μm thick silicon sample. The measured SHEL displacements for a p-polarized probe beam are obtained between −10 to 150 nm as a function of the angle of incidence on the sample. Different angles of incidence are achieved by keeping a fixed angular separation between the pump and the probe beams while rotating the sample about the axis perpendicular to the plane of incidence. In another experiment, an optically thin (500 nm thick) GaAs sample allows one to use Pauli-blocking as an optical interaction to investigate the polarization and angular dependence of the SHEL in the probe beam. For such a polarization-dependent imaging technique, the SHEL displacement in the pump beam also contributes to the measured signal and is evaluated experimentally. A probe beam at normal incidence is used to measure a SHEL displacement of ∼180 nm in a transmitted p-polarized pump beam impinging on the sample with an angle of incidence of 55 degrees. Finally, two-photon absorption is used to resolve the SHEL in a (001) oriented 500 μm thick GaAs wafer using an optical source generating sub-bandgap radiation (λ = 1550 nm) with a pulse duration of 120 fs. Linearly p- and s- co-polarized pump and probe beams are also used to investigate the polarization dependence of the SHEL. All the experimental results obtained using these different optical interactions agree with the theory within the experimental error. Finally, analytical expressions of the shifts experienced by the circular components of a beam impinging at an interface between two optical media are also derived for an incident beam with an arbitrary spatial distribution.