Resonance fluorescence of laser-driven highly charged ions is investigated with regard to precisely measuring atomic properties. For this purpose an ab initio approach based on the Dirac equation is employed that allows for studying relativistic ions. These systems provide a sensitive means to test correlated relativistic dynamics, quantum electrodynamic phenomena and nuclear effects by applying x-ray lasers. We show how the narrowing of sidebands in the x-ray fluorescence spectrum by interference due to an additional optical driving can be exploited to determine atomic dipole or multipole moments to unprecedented accuracy.
Resonance fluorescence of laser-driven highly charged ions is investigated with regard to precisely measuring atomic properties. For this purpose an ab initio approach based on the Dirac equation is employed that allows for studying relativistic ions. These systems provide a sensitive means to test correlated relativistic dynamics, quantum electrodynamic phenomena and nuclear effects by applying x-ray lasers. We show how the narrowing of sidebands in the x-ray fluorescence spectrum by interference due to an additional optical driving can be exploited to determine atomic dipole or multipole moments to unprecedented accuracy.
In this thesis we investigate strong-field relativistic processes in highly charged ions. In the first part,we study resonance fluorescence of laser-driven highly charged ions in the relativistic regime by solving the time-dependent master equation in a multi-level model. Our ab initio approach based on the Dirac equation allows for investigating highly relativistic ions, and, consequently, provides a sensitive means to test correlated relativistic dynamics, bound-state quantum electrodynamic phenomena and nuclear effects by applying coherent light with x-ray frequencies. Atomic dipole or multipole moments may be determined to unprecedented accuracy by measuring the interference-narrowed fluorescence spectrum. Furthermore, we investigate the level structure of heavy hydrogenlike ions in laser beams. Interaction with the light field leads to dynamic shifts of the electronic energy levels, which is relevant for spectroscopic experiments. We apply a fully relativistic description of the electronic states by means of the Dirac equation. Our formalism goes beyond the dipole approximation and takes into account non-dipole effects of retardation and interaction with the magnetic field components of the laser beam. We predicted cross sections for the inter-shell trielectronic recombination (TR) and quadruelectronic recombination processes which have been experimentally confirmed in electron beam ion trap measurements, mainly for C-like ions, of Ar, Fe and Kr. For Kr30+, inter-shell TR contributions of nearly 6% to the total resonant photorecombination rate were found.
Resonance fluorescence of laser-driven atoms is studied in the relativistic regime by solving the time-dependent Dirac equation in a multi-level model. Electron spin and retardation of the electron–photon interaction give rise to new phenomena such as splitting of sideband peaks and modification of the Rabi oscillator frequencies not explainable in a nonrelativistic theory. In our theoretical investigation, we show how, by applying coherent light with x-ray frequencies, the relativistic fluorescence spectrum can be exploited to determine atomic multipole matrix elements.
We present the relativistic power spectrum for the interaction of an x-ray field with an highly charged ion, obtained by solving the time-dependent Dirac equation in a two-level approximation [1]. The phenomenon of splitting of sideband peaks is obtained as a consequence of the introduction in theory of the electronic spin. Also this phenomenon together with the retardation of the electron-photon interaction changes the values of Rabi frequencies. After describing the fluorescence spectrum, we show how it can be used to determine atomic multipole matrix elements.
The incoherent inelastic part of the resonance fluorescence spectrum of a laser-driven atom is known as the Mollow spectrum [B. R. Mollow, Phys. Rev. 188, 1969 (1969)]. Starting from this level of description, we discuss theoretical foundations of high-precision spectroscopy using the resonance fluorescence light of strongly laser-driven atoms. Specifically, we evaluate the leading relativistic and radiative corrections to the Mollow spectrum, up to the relative orders of ${(Z\ensuremath{\alpha})}^{2}$ and $\ensuremath{\alpha}{(Z\ensuremath{\alpha})}^{2}$, respectively, and Bloch-Siegert shifts as well as stimulated radiative corrections involving off-resonant virtual states. Complete results are provided for the hydrogen $1S\text{\ensuremath{-}}2{P}_{1∕2}$ and $1S\text{\ensuremath{-}}2{P}_{3∕2}$ transitions; these include all relevant correction terms up to the specified order of approximation and could directly be compared to experimental data. As an application, the outcome of such experiments would allow for a sensitive test of the validity of the dressed-state basis as the natural description of the combined atom-laser system.
Fundamental interactions and symmetries define the structure and properties of all matter, in particular of its small and diverse visible constituents—the atoms. The study of their distinctive spectra through precision spectroscopy is therefore a vital tool to advance our understanding of nature. Highly charged ions (HCIs) constitute the largest fraction of all atoms since every atom has as many charge states as electrons it can bind. Although most of the matter on Earth is neutral, HCIs are ubiquitous in the universe and their systematic study is essential not only for atomic physics but eminently for astrophysics, nuclear physics, and fusion research, among others. Recently, HCIs have been identified as ideal candidates for sensitive tests of physics beyond the Standard Model of particle physics and for use in future high-accuracy optical atomic clocks. However, the realization of such proposals has been hindered by the hitherto constrained laboratory control and limited spectroscopic accuracy of about parts-per-million fractional uncertainty levels. This thesis reports the first coherent laser spectroscopy of HCIs, boosting the achievable spectroscopic precision by eight orders of magnitude compared to traditional spectroscopy methods. The 2P1/2–2P3/2 fine-structure ground-state transition in highly charged 40Ar13+ at an optical wavelength of 441 nm was chosen as a proof-of-principle case. A single ion of this species was isolated from a megakelvin-hot plasma cloud and co-trapped together with a laser-cooled singly charged 9Be+ ion in a two-ion crystal, confined in the harmonic potential of a cryogenic linear Paul trap. This coupled quantum-mechanical system was then cooled to its ground state of axial motion, corresponding to the lowest temperature of a HCI ever achieved. The spectroscopy was realized by implementing quantum logic techniques which allow preparation of the quantum state of the HCI and to map its electronic state after spectroscopy onto the 9Be+ logic ion in order to detect it there with high efficiency through electron shelving. In addition to the increase of spectroscopic precision, the excited-state lifetime and g-factor were measured—the latter one to unprecedented accuracy, resolving effects from special relativity, interelectronic interactions, and quantum electrodynamics. Moreover, it settled a discrepancy between theoretical predictions. The demonstrated techniques are not limited to the specific 40Ar13+ species but universally applicable to other HCIs. Thereby, this work unlocks the potential of HCIs for unrivaled tests of fundamental physics, the search for new physics—such as a 5th force, variations of fundamental constants and dark matter candidates—as well as the use of HCIs in novel optical atomic clocks.
One active topic in Atomic Physics is the study of highly charged ions (HCI). These physical systems have a strong Coulomb field that provides a unique opportunity to investigate and validate relativistic, Quantum ElectroDynamics (QED), and many-body e ects. Moreover, fundamental test on symmetries and parity violation gives clues to the physics beyond the Standard Model. Thus, nowadays, a primary goal of Atomic Physics is the existence of precise experimental data and accurate theoretical calculations for these systems. In this thesis I focus on the investigation of forbidden radiative transitions in HCI. The main emphasis of this work is on atomic transitions, in which the selection rules forbids the emission of electric dipole photons. In this special type of radiative transition, the electron decays mainly through the emission of a single magnetic dipole photon, or two electric dipole photons. Both types of decay are investigated either experimentally or theoretically. The two-photon decay is only theoretically investigated, using a full relativistic formalism,in HCI with one or two electrons. Several physical e ects in the two photon decay, such as resonances, the Dirac’s negative continuum or angular correlations are considered. Related with the decay, two-photon excitation is also investigated. According to these evaluations, I stress the importance of relativistic and nondipolar e ects. Moreover, a new approach based on the B-polynomials basis set is employed on two-photon transitions. The second part of the work is devoted to the precise measurement of transitions in highly charged Ar with two to four electrons. For that matter, I describe the technical features of a double crystal spectrometer used to perform those measurements in HCI for the first time. This kind of spectrometer is able to perform absolute and precise measurements with an accuracy never achieved in these systems, which enables a comparison with recent QED calculations. I describe a Monte-Carlo code developed with the purpose of studying several systematic errors, as well as testing the various methods of retrieving physical quantities from raw data. Finally, I present the first absolute 2 ppm measurements on HCI with this spectrometer, paying special attention on the forbidden magnetic dipole transition in He-like Ar.