The bound-bound transition from the 5d²6s² ³F_2 ground state to the 5d6s²6p ³D_1 excited state in negative lanthanum has been proposed as a candidate for laser cooling, which has not yet been achieved for negative ions. Anion laser cooling holds the potential to allow the production of ultracold ensembles of any negatively charged species. In this work the aforementioned transition was studied in a beam of negative La ions by high-resolution laser spectroscopy. The center-of-gravity frequency of the transition was measured to be 96.592 80(10) THz. Seven of the nine expected hyperfine structure resonances were resolved. The observed peaks were unambiguously assigned to the predicted hyperfine transitions by a fit. From the determined hyperfine structure for this transition it was concluded that only three lasers would be required to cool and re-pump all hyperfine levels. Furthermore, the observed relative transition amplitudes suggest that in resonance the transitions are saturated at a laser power of 45 W/m². A rough estimate of the transition cross section confirms that La‾ is a promising candidate for the first laser cooling of negative ions.

Within this thesis, molecular dynamics of diatomic molecules is studied using the XUV–IR pump–probe technique. Here, a single extreme ultraviolet (XUV) photon created by high-harmonic generation ionizes the diatomic target molecule. The initiated dynamics is probed after a variable time delay by an ultrashort (12 fs) infrared (IR) laser pulse. The 3-dimensional momenta of all charged fragments are measured using a reaction microscope. In an experiment on O_2, a nuclear wave-packet oscillation is observed on the binding potential-energy curve (PEC) of the O_2^+(a ^4Π_u) electronic state. By comparing simulated results with experimental data, theoretically predicted PECs are tested. The experimental results are best reproduced if the wave packet is propagated on a Morse potential adjusted to the experimental data. This demonstrates the sensitivity of our method and its ability to predict accurate PECs from the measured wave-packet evolution. In an N2 experiment, the pump–probe delay dependent yield of stable N_2^+ is observed. It is interpreted as a sequential double ionization via a highly excited antibonding cationic state. The dissociation of the intermediate state is temporally resolved and can be interrupted by multi-photon ionization with the IR pulse within ≈ 15 fs after XUV ionization.

Various nonlinear electrodynamic and electroweak processes in strong plane-wave laser fields are considered with an emphasis on short-pulse effects. In particular, the momentum distribution of photoproduced electron-positron pairs is calculated numerically and a semiclassical interpretation of its characteristic features is established. By proving the optical theorem, compact double-integral expressions for the total pair-creation probability are obtained and numerically evaluated. The exponential decay of the photon wave function in a plane wave is included by solving the Schwinger-Dyson equations to leading-order in the quasistatic approximation. In this respect, the polarization operator in a plane wave is investigated and its Ward-Takahashi identity verified. A classical analysis indicates that a photoproduced electron-positron pair recollides for certain initial conditions. The contributions of such recollision processes to the polarization operator are identified and calculated both analytically and numerically. Furthermore, the existence of nontrivial electron-spin dynamics induced by quantum fluctuations is verified for ultra-short laser pulses. Finally, the exchange of weak gauge bosons is considered, which is essential for neutrino-photon interactions. In particular, the axial-vector--vector coupling tensor is calculated and the so-called Adler-Bell-Jackiw (ABJ) anomaly investigated.

Ultrahigh energy cosmic rays are extreme energetic particles from outer space. They have aroused great interest among scientists for more than fifty years. However, due to the rarity of the events and complexity of the process of their propagation to Earth, they are still one of the biggest puzzles in modern high energy astrophysics. This dissertation is dedicated to study the origin of ultrahigh energy cosmic rays from various aspects. Firstly, we discuss a possible link between recently discovered sub–PeV/PeV neutrinos and ultrahigh energy cosmic rays. If these two kinds of particles share the same origin, the observation of neutrinos may provide additional and non-trivial constraints on the sources of ultrahigh energy cosmic rays. Secondly, we jointly employ the chemical composition measurement and the arrival directions of ultrahigh energy cosmic rays, and find a robust upper limit for distances of sources of ultrahigh energy cosmic rays above ∼ 55EeV, as well as a lower limit for their metallicities. Finally, we study the shear acceleration mechanism in relativistic jets, which is a more efficient mechanism for the acceleration of higher energy particle. We compute the acceleration efficiency and the time-dependent particle energy spectrum, and explore the feature of synchrotron radiation of the accelerated particles. The possible realizations of this mechanism for acceleration of ultrahigh energy cosmic rays in different astrophysical environments is also discussed.

Various nuclear effects in atomic systems and in a particular type of solids, namely, in unconventional superconductors, are investigated. The first process considered, internal pair conversion in heavy ions, can play an important role in numerous scattering processes to be examined at existing or upcoming high-energy heavy-ion-accelerator facilities. The rate of nuclear excitation and thus the number of created pairs is found here to be strongly increased by ion planar channeling through a crystal. The time-reversed process of pair conversion, nuclear excitation by resonant positron annihilation, provides an alternative mechanism of positronmatter interaction and constitutes a state-selective way to excite nuclei which is complementary to photo- and Coulomb excitation. Furthermore, weak-interaction effects are examined in the context of parity violation in unconventional p-wave superconductors. We suggest schemes to effciently enhance the effect and to enable its future experimental study. The considered effects represent new phenomena at the interface of atomic and nuclear physics and quantum electrodynamics, and provide effective ways to investigate fundamental interactions.

The ideal Penning trap consists of a homogeneous magnetic field and an electrostatic quadrupole potential. In this configuration, the three characteristic eigenfrequencies of a trapped particle do not depend on its motional amplitudes from a classical point of view. However, this three-fold harmonicity of the eigenmotions is compromised by higher-order terms in the magnetic field and electric potential, and ultimately by special relativity. Understanding the systematic effect of these deviations on the motional frequencies is crucial for accurate measurements.

This thesis calculates numerous frequency-shifts in the framework of classical perturbation theory working with equations of motion for the particle's trajectory. Starting from a general parametrization of cylindrically-symmetric electric and magnetic imperfections in cylindrical coordinates, it is shown how to calculate the corresponding first-order frequency-shift consistently. Relativistic frequency-shifts are handled perturbatively in the relativistic equations of motion rather than via a quantum-mechanical operator formalism. Other frequency-shifts considered include the effect of a slightly elliptic quadrupole potential, the interaction of an ion with its image charges induced in the trap electrodes, and a small modulation of the quadrupole potential. The frequency-shifts derived are translated into shifts under the operation mode of locked axial-frequency used by the THe-Trap experiment.

The reactor antineutrino experiment Double Chooz aims to provide a precise measurement of the neutrino mixing angle θ₁₃. In the analysis with one detector, accuracy in the predicted neutrino spectrum from simulation is a necessity with regard to normalization and energy shape. The detection efficiency of neutron events, which are part of the coincidence signal created by neutrinos, introduce the largest uncertainty contribution of the normalization of the experiment related to the signal detection. In order to accomplish a matching of the efficiencies observed in data and simulation, a correction of the Monte Carlo normalization and an associated systematic uncertainty are inputs in the θ₁₃ analysis. Calibration source deployments in the inner two detector volumes allow for a measurement of the neutron detection efficiency using ²⁵²Cf fission neutrons. New methods enable to compute the correction integrated over the whole volume and the corresponding uncertainty of the selection cut related efficiency. With these revised approaches a factor two improvement in the detection efficiency uncertainty was achieved. The correction of the neutron capture fraction – the capture fraction quantifies the proportion of captures on a particular element – is evaluated and tested for its robustness. Furthermore, a crosscheck of this quantity is discussed using neutrons produced by cosmic muon spallation. Finally, the uncertainty on border effects, emerging from neutron migration at the fiducial volume boundaries, is estimated by means of different Monte Carlo configurations with varying parameters and neutron physics modelings.

The novel Penning-trap mass spectrometer PENTATRAP aims at mass-ratio determinations of medium-heavy to heavy ions with relative uncertainties below 10^−11. From the mass ratios of certain ion species, the corresponding mass differences will be determined with sub-eV/c^2 uncertainties. These mass differences are relevant for neutrino-mass experiments, a test of special relativity and tests of bound-state QED. Means to obtain the required precision are very stable trapping fields, the use of highly-charged ions produced by EBITs, a non-destructive cyclotron-frequency determination scheme employing detectors with single-ion sensitivity and a five-trap tower, that allows for measurement schemes being insensitive to magnetic field drifts.

Within this thesis, part of the detection electronics was set up and tested under experimental conditions. A single-trap setup was realized. A Faraday cup in the trap tower enabled the proper adjustment of the settings of the beamline connecting the EBIT and the Penning-trap system, resulting in the first trapping of ions at PENTATRAP. A stabilization of switched voltages in the beamline and detailed studies of ion bunch characteristics allowed for reproducible loading of only a few ions. Detection of the axial oscillation of the trapped ions gave hints that in some cases, even single ions had been trapped. Furthermore, valuable conclusions about necessary modifications of the setup could be drawn.

Die Emissions- und Absorptionslinien von K-Schalen-Übergängen in hochgeladenen Eisenionen gehören zu den bedeutendsten Charakteristika in den Röntgenspektren vieler astronomischer Objekte. Sie werden verwendet, um Eigenschaften und Dynamik heißer astrophysikalischer Plasmen zu bestimmen, wozu eine genaue Kenntnis der Übergangsraten, und insbesondere des Verhältnisses von radiativem und autoionisierendem Zerfall, benötigt wird. Diese waren bisher jedoch nur aus theoretischen Berechnungen bekannt. In der vorliegen Arbeit wurden erstmals absolute Zerfallsraten von radiativen und autoionisierenden Übergängen in lithiumartigen, berylliumartigen und kohlenstoffartigen Eisenionen experimentell bestimmt. Dazu wurden die Ionen in einer Elektronenstrahlionenfalle erzeugt und durch Röntgenstrahlung des Synchrotrons PETRA III resonant angeregt. Durch Anwendung einer neu entwickelten Messmethode, bei der gleichzeitig der Auger- und der radiative Zerfall beobachtet wurden, konnten systematische Unsicherheiten stark reduziert werden, wodurch Genauigkeiten besser als 10% erreicht wurden.

Atomic masses and hence binding energies of nuclides are of great importance for studies of nuclear structure since they reflect all effective interactions in a nucleus. Within this thesis the masses of seven nuclides, namely 194Au, 194Hg, 190,193,198Tl and 202,208Pb, were determined at the Penning-trap mass spectrometer ISOLTRAP at ISOLDE/CERN. The thallium region in the chart of isotopes is of special interest due to the occurrence of nuclear structure effects like low-lying isomers, level inversion, shape coexistence and deformations. These effects are investigated by applying finite-difference mass formulas, such as the two-neutron separation energies or the so-called empirical pairing gaps. The second topic addressed within the present thesis is an ultra-stable voltage source, called StaReP (Stable Reference for Penning Trap Experiments), which was developed at the Max-Planck-Institut für Kernphysik. It is one of the key components of the high-precision mass spectrometer PENTATRAP, containing a tower of five Penning traps. A 25-channel voltage source with a relative stability of few 10^−8 over a period of 10 minutes in the range of 0 to −100V is mandatory for PENTATRAP aiming for mass measurements with relative mass uncertainties of ≤ 10^−11. Mass values with such a high precision allow for stringent tests of quantum electrodynamics in strong electric fields, testing Einstein’s mass-energy relation E = mc^2 as well as measurements of decay energies (Q-values) with applications in neutrino physics.