2020-10-24T14:32:14Zhttp://edoc.mpg.de/ac_ft_oai.ploai:edoc.mpg.de:2077022005-07-0837:954
Time Reversal and Exceptional Points
Harney, H. L.
Heiss, W. D.
expertsonly
Eigenvectors of decaying quantum systems are studied at exceptional points of the Hamiltonian. Special attention is paid to the properties of the system under time reversal symmetry breaking. At the exceptional point the chiral character of the system - found for time reversal symmetry - generically persists. It is, however, no longer circular but rather elliptic.
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag 2004
2004
Article
http://edoc.mpg.de/207702
info:doi/10.1140/epjd/e2004-00049-7
The European Physical Journal D, v.29, 429-432 (2004)
en
oai:edoc.mpg.de:2846502008-03-0337:954
Theory Advances in High-Precision Two-Photon Spectroscopy
Haas, Martin
expertsonly
¨ High-precision two-photon spectroscopy of hydrogen and hydrogenlike systems constitutes an exceptional tool for experimental tests of fundamental theories. In the analysis of these experiments, theory also plays a vital role in the modeling of time-resolved spectra, the calculation of precise transition matrix elements, and the correction of a number of systematic e ects. This thesis gives a detailed analysis of the relevant two-photon excitation dynamics, starting from the single-atom response and leading to a Monte Carlo model which can be used for the analysis of atomic beam experiments. Dynamic polarizabilities of relevant S and D states, quantifying the dynamic Stark shift, and transition matrix elements among these states are calculated, taking into account leading-order relativistic, radiative and non-dipole laser-field e ects. An important broadening e ect of the experimentally observed spectra in the hydrogen 1S 2S spectroscopy experiment at the Max Planck Institut f¨ur Quantenoptik (MPQ) is identified and quantitatively described, as well as systematic frequency shifts. Corresponding possible improvements to the experimental setup are proposed. By combining the results of repeated MPQ hydrogen 1S 2S measurements and other experiments, in collaboration with the MPQ group, separate stringent limits on the possible drift of the magnetic moment of the cesium nucleus and the finestructure constant are deduced.
1 Introduction
2 Two-Photon Excitation Dynamics
2.1 Introduction
2.2 Basic quantum dynamics
2.2.1 Analytic solution for constant intensity
2.2.2 Quantum dynamics including spontaneous decay
2.3 Generalizations of the equations of motion
2.3.1 Motion in a standing wave and time-dependent intensity 2.3.2 Further generalizations
2.4 Analytic solution including ionization and spontaneous decay
3 Transition Matrix Elements and Dynamic Polarizability
3.1 Introduction
3.2 Overview of the interactions of atom, laser mode and vacuum
3.2.1 Second-order perturbation
3.2.2 Fourth order perturbation
3.2.3 Transition matrix elements
3.3 Calculation of two-photon transition matrix elements
3.3.1 Calculational method
3.3.2 Results for two-photon transitions
3.4 Dynamic Stark e ect
3.4.1 Classical field approach
3.4.2 Second-quantized approach
3.5 Calculation of the AC Stark shift
3.5.1 Matrix elements
3.5.2 Results for two-photon transitions
3.6 Calculation of the photoionization cross section
3.7 Combined induced-spontaneous two-photon decay
3.8 Conclusion
4 Relativistic and Radiative Corrections to Dynamic Processes
4.1 Perturbation to the dynamic polarizability
4.2 Perturbation to the transition matrix element
4.3 Potential for relativistic corrections
4.4 Potential for radiative corrections
4.5 Calculation of relativistic and radiative corrections
4.5.1 Wavefunction contributions
4.5.2 Eigenenergy contributions
4.5.3 Hamiltonian contributions
4.5.4 Results for S S transitions
4.6 Beyond the dipole approximation
4.6.1 Field-configuration dependent corrections
4.6.2 Results for two-photon transitions
4.7 Lamb shift of laser dressed states
5 Monte Carlo Investigations and Lineshape
5.1 Introduction
5.2 Experimental setup
5.3 Implementation of the simulation
5.4 Photoionization broadening of the 1S 2S transition line shape
5.4.1 Introduction
5.4.2 Experimentally observed broadening and shift coe cients
5.4.3 Simulated broadening and shift coe cients
5.4.4 Comparison .
5.4.5 Laser line width
5.5 E ects of nozzle freezing
5.6 E ect of laser beam misalignment
5.6.1 The αθ-term
5.6.2 The α²-term
5.7 Conclusion
6 1S-2S Spectroscopy and Possible Drift of Fundamental Constants
6.1 Data analysis and systematic effects
6.1.1 MPQ data analysis procedure
6.1.2 Models for the velocity distribution
6.1.3 Full line shape model and Lorentz data analysis
6.1.4 Weighting and Χ²r in the data regression
6.1.5 Effect of unsteady power calibration
6.1.6 Freezing nozzle
6.1.7 Power-dependent line shape model
6.2 Test of the drift of fundamental constants
6.2.1 Introduction
6.2.2 Analysis of the laboratory measurements
6.2.3 Results
7 Conclusion 133 7.1 General conclusion
7.2 Proposals for future experiments
A Some comparisons with the literature
A.1 The 1S-2S transition
A.2 The 1S-3S transition
A.3 Light shifts
B Explicit Polarizabilities and Transition Matrix Elements Bibliography
Ruprecht-Karls-Universität Heidelberg
2006
PhD-Thesis
http://edoc.mpg.de/284650
en
oai:edoc.mpg.de:3017822008-03-0337:954
Bremsstrahlung in a Circularly Polarized Laser Field
Schnez, Stephan
expertsonly
In this diploma thesis, we evaluate the process of laser-assisted bremsstrahlung. In the usual,
well-known bremsstrahlung process, an electron scatters off a Coulomb potential and spontaneously
emits a photon. Here, the same process is considered, but in the presence of a strong,
circularly polarized laser field. The intensities of the lasers we consider here are in the range of
1019 W/cm2 to 1021 W/cm2 so that a fully relativistic description is necessary. Consequently, we
use a quantum-electrodynamical approach. In our formalism, we take the laser field into account
by using the solutions of the Dirac equation coupled to an external field { the so-called Volkov
solutions. Apart from the theoretical derivation of the laser-dressed bremsstrahlung cross section,
the numerical evaluation of the resulting expression with the help of a self-written Fortran
90 programme is an essential part of the thesis at hand. One of the main results is that the
cross section shows resonances at { depending on the scattering geometry { integer multiples of
the laser frequency. In other words, we have higher harmonic generation in the bremsstrahlung
process.
1 Introduction and Notation 1
1.1 Introduction 1
1.2 Units and Notation 4
1.3 The Ponderomotive Energy 6
2 Derivation of the Bremsstrahlung Cross Section 7
2.1 Volkov Solutions of the Dirac Equation 8
2.2 The Full, Laser-Dressed Electron Propagator 11
2.3 The Vector Potentials A Coul(x) and b,γ(x) 13
2.4 The S-Matrix and the Cross Section 14
2.4.1 Limit of Vanishing Laser Field a → 0 18
2.4.2 Integrated Cross Section 19
2.5 Resonances and Higher Harmonic Generation 19
2.6 Finite Peaks { the Imaginary Mass and Energy 21
2.7 Explicit Calculation of the Cross Section 23
3 The Numerical Evaluation 27
3.1 Overview over the Whole Programme 27
3.2 Implementation of the Minkowski Metric and the Dirac Algebra 29
3.3 The Numerical Integration over dΩ f< 30
3.4 Calculation of the Differential Cross Section 33
3.5 Calculation of the Imaginary Mass and Energy Shift 36
3.6 Numerical Tests of the Validity of the Code 37
4 Results 41
4.1 Comparison between the Free and the Laser-Dressed Electron Propagator 41
4.2 Comparison with and without Imaginary Mass and Energy 43
4.3 Differential Cross Sections 43
4.4 Total Cross Sections 47
4.5 The Peculiar Behaviour for a Varying Laser Intensity 49
5 Summary and Outlook 53
A Derivation of the Bethe-Heitler Cross Section 57
B Classical Motion of an Electron 63
C The Role of the Interference Term 67
D Dirac Algebra and the Free Dirac Spinor 69
E Bessel Functions and Generalized Bessel Functions 71
F Derivation of S(1)fi 77
G Main Structure of the Programme 83
University of Heidelberg
2006
Thesis
http://edoc.mpg.de/301782
en
oai:edoc.mpg.de:3139732008-03-1937:954
Optimization of high-order harmonic generation in laser-driven atomic and molecular systems
Fischer, Robert
expertsonly
When an atom or a molecule is subject to a strong laser pulse a recollision-recombination mechanism gives rise to the emission of high-order harmonic radiation containing frequency multiples of the irradiating laser field. This radiation is nowadays the basis for the highly active research field of attosecond physics. The laser magnetic field is responsible for the drift of ejected electron wave packets in the laser propagation direction. In the context of the first project of this thesis, it has been found that the harmonic radiation which is induced by this drift motion can be sensitively influenced by means of an additional relatively weak static magnetic field. In the second project, a novel mechanism is proposed which combines the drift in the laser propagation direction with the properties of antisymmetric orbitals. In a regime of high laser intensities, efficient high-order harmonic generation is proven to be possible without the common limitations due to the drift in the laser propagation direction. From a different viewpoint, it has been shown for the first time that this drift leads to an increase in harmonic intensity. The main results have been obtained by numerical integration of the time-dependent Schr¨odinger equation.
Ruprecht-Karls-Universtät
2007
PhD-Thesis
http://edoc.mpg.de/313973
oai:edoc.mpg.de:3152672007-05-2337:954
Lossless Negative Refraction in Dense Atomic Gases
Orth, Peter Philipp
expertsonly
Ruprecht-Karls-Universität
2007
Thesis
http://edoc.mpg.de/315267
oai:edoc.mpg.de:3209262007-10-1937:954
Coherence effects in vacuum-induced processes
Kiffner, Martin
expertsonly
Quantum interference and coherence effects in the interaction of atoms with the quantized electromagnetic field are investigated theoretically. A general master equation for the description of atom-field interactions is introduced. The interplay of the concepts of complementarity and interference in the time-energy domain are studied on the basis of the fluorescence light emitted by a single laser-driven atom, where the coherence of spontaneous processes gives rise to quantum interference in the spectrum of resonance fluorescence. The vacuum-induced dipole-dipole interaction in pairs of multi-level atoms is analyzed. It is shown that the interaction between orthogonal transition dipole moments of different atoms does not only in- fluence the system dynamics crucially, but implies that the few-level approximation in general cannot be applied to near-degenerate Zeeman sublevels of the atomic level scheme. Potential applications of dipole-dipole interacting multi-level atoms for the implementation of decoherence-free subspaces and the generation of entanglement between atomic states are examined. The generation of an entangled state of the radiation field with a macroscopic number of photons is discussed on the basis of a single-atom laser.
Ruprecht-Karls Universität
2007
PhD-Thesis
http://edoc.mpg.de/320926
en
oai:edoc.mpg.de:3224422007-11-1437:954
Relativistische Rekollisionen in starken Laserfeldern
Klaiber, Michael
expertsonly
The relativistic ionization-recollision process is investigated theoretically. In order to treat the problem analytically a gauge-invariant version of the strong-field approximation is developed and employed to describe above-threshold ionization (ATI) as well as highharmonic generation (HHG). Relativistic calculations of the corresponding energy spectra show a strong suppression of the recollision of the ionized electron with the atomic core in conventional laser fields compared to the nonrelativistic approach. Three different proposals based on a modification of the driving laser via the use of attosecond laser pulse trains are presented that circumvent this problem and allow the recollision of the ionized electron in the relativistic regime. In this way coherent radiation with energies up to 10 MeV and zeptosecond -ray pulses via the HHG-process become feasible.
Ruprecht-Karls Universität
2007
PhD-Thesis
http://edoc.mpg.de/322442
de
oai:edoc.mpg.de:3284372009-09-0137:954
Energy absorption, ionization, and harmonic emission in laser-irradiated atomic clusters
Kundu, Mrityunjay
expertsonly
The excellent coupling of laser light to atomic clusters is a known, experimentally established fact. However, the physical mechanism of laser absorption is still controversially discussed. Linear resonance (LR) absorption occurs for sufficiently long laser pulses of optical or longer wavelengths. Here the Mie-plasma frequency initially rises above the laser frequency, then drops due to cluster expansion and therefore meets the laser frequency at some point. Instead, in few-cycle laser pulses this LR is not met but efficient laser energy absorption is found to persist. By particle-in-cell simulations and analytical modelling it is shown that the cluster electrons contributing to efficient absorption pass a nonlinear resonance (NLR), i.e., the instantaneous frequency of their motion in a time-dependent, anharmonic potential transiently meets the laser frequency. For a given laser intensity and cluster it is further shown that an optimum laser wavelength for absorption exists which typically lies in the ultraviolet regime. This yields a higher laser absorption efficiency than employing LR during the cluster expansion. The emission spectrum of laser-irradiated clusters is also investigated. Only the deeply bound, coherently oscillating electrons in the cluster potential contribute to low-order harmonic emission. In contrast, electrons crossing the NLR and leaving the cluster emit radiation with random phase which inhibits high-order harmonics. A pump-probe experiment is proposed to measure the time-dependent nano-cluster charge density by detecting the harmonic radiation.
Ruprecht-Karls-Universität
2007
PhD-Thesis
http://edoc.mpg.de/328437
oai:edoc.mpg.de:3517192008-10-2837:954
Laser-assisted second-order relativistic QED processes: Bremsstrahlung and pair creation modified by a strong electromagnetic wave field
Lötstedt, Erik
expertsonly
The primary aim of this thesis is to advance the understanding of higher-order laser-assisted relativistic processes within quantum electrodynamics (QED), which necessitates a formulation using fully laser-dressed fermion propagators. This study is motivated by presently available laser sources which routinely produce electromagnetic fields strong enough to accelerate the electron to velocities close to the speed of light. The strong laser-matter interaction requires an all-order treatment, different from the perturbative expansion of the usual QED. In this thesis, the influence of a strong laser field on two fundamental processes of QED is studied theoretically. The first process, bremsstrahlung from an electron scattered at the Coulomb potential of a nucleus, is found to show a resonant behavior in the presence of the laser. The cross section is numerically evaluated from the formula resulting from applying the strong-field Feynman rules. The second process, electron-positron pair creation by a gamma photon and a Coulomb field is studied in the case when the laser field strength is below the critical field. Here the total cross section is unchanged by the laser, while the differential cross section is drastically modified. Finally, a detailed study and a novel evaluation algorithm of the generalized Bessel function, a special function occurring naturally in laser-modified QED, is presented.
Ruprecht-Karls-Universität
2008
PhD-Thesis
http://edoc.mpg.de/351719
en
oai:edoc.mpg.de:3595482009-09-0137:954
Höhere QED-Bindungs-Korrekturen unter besonderer Berücksichtigung der Selbstenergie
Wundt, Benedikt Johannes Wilhelm
expertsonly
In this work, higher order QED binding corrections to the self-energy are calculated. It is our aim to determine the non-logarithmic contribution of the order α(Zα)6, which has proven to be a difficult task in the past. This is because due to the two energy scales present in the problem, one has to apply methods of quantum field theory as well as of relativistic atomic physics. These two energy scales are seperated by introducing an overlapping parameter. We present a numerical method where we use a discrete complete basis set on a lattice which allows us to avoid the problems encountered in the previous methods. Therefore, we can calculate this contribution for higher excited states that are important for high-precision spectroscopy but have not been accessible using previous methods.
Ruprecht-Karls-Universität
2007
Thesis
http://edoc.mpg.de/359548
de
oai:edoc.mpg.de:3663772008-07-0237:954
Gebunden-freie Paarerzeugung in kombinierten Laser- und Coulombfeldern
Deneke, Carlus Clemens
expertsonly
In the present work, the process of bound-free pair production of electrons and positrons in combined laser and Coulomb fields is investigated. It is assumed that an ion at relativistic speed collides with an intense x-ray laser beam. The process proceeds nonlinearly due to simultaneous absorption of several laser photons. The capture of the electron into the ground state and excited states is considered. The process probability is calculated in the framework of relativistic quantum mechanics. For this nonlinear process ordinary perturbation theory cannot be applied; instead the Strong-Field-Approximation is used,which neglects the influence of the Coulomb field on the positron. An analytical result for the amplitude is derived and numerical results of pair production rates for parameters for the planned x-ray laser at DESY are presented. The main outcome is that bound-free pair production has a sizeable probability and that it is comparable to the free-free reaction channel. Experimental observation of this process will become feasible in the near
future.
Ruprecht-Karls Universität
2008
Thesis
http://edoc.mpg.de/366377
de
oai:edoc.mpg.de:3674112008-07-1737:954
Negative Refraction in Atomic Two-Component Media
Jungnitsch, Bastian
expertsonly
Negative Refraction in Atomic Two-ComponentMedia: In the present thesis we study the feasibility of negative refraction at optical wavelengths and low absorption in gases consisting of two species of atoms. Compared to a single-component system, we expect it to be easier to find candidates for an experimental realization due to less stringent conditions that must be met. The two involved species contribute the electric and the magnetic response, respectively. To obtain a negative refractive index, both responses must be large. Therefore, we optimize the magnetic susceptibility, which typically is considerably smaller than the electric susceptibility, in different systems. Moreover, we investigate a mechanism in so-called closed-loop systems that enhances the magnetic response by a factor of 1, the inverse fine structure constant. Closed-loop configurations are characterized by the fact that the coupling control and probe fields build up a closed interaction loop in the level scheme. We find that the enhancement occurs, as the electric probe field component scatters into the magnetic probe transition. Using the previous results, we calculate the refractive index for several combinations of two realistic level schemes and address the occurring instabilities of the probe field. We obtain a refractive index of n = 6.4 and n = 3.7, respectively, at vanishing absorption for two different systems.
Ruprecht-Karls Universität
2008
Thesis
http://edoc.mpg.de/367411
en
oai:edoc.mpg.de:3775452008-09-1537:954
Coherence and interference in quantum optics
Evers, Jörg
expertsonly
Ruprecht-Karls Universität
2008
Habilitation
http://edoc.mpg.de/377545
en
oai:edoc.mpg.de:3952072008-12-0437:954
Ionization and bound-state relativistic quantum dynamics in laser-driven multiply charged ions
Hetzheim, Henrik
expertsonly
The interaction of ultra-strong laser fields with multiply charged hydrogen-like ions can be distinguished in an ionization and a bound dynamics regime. Both are investigated by means of numerically solving the Dirac equation in two dimensions and by a classical relativistic Monte-Carlo simulation. For a better understanding of highly nonlinear physical processes the development of a well characterized ultra-intense relativistic laser field strength has been driven forward, capable of studying e.g. the magnetic field effects of the laser resulting in an additional electron motion in the laser propagation direction. A novel method to sensitively measure these ultra-strong laser intensities is developed and employed from the optical via the UV towards the XUV frequency regime. In the bound dynamics field, the determination of multiphoton transition matrixelements has been investigated between different bound states via Rabi oscillations.
Ruprecht-Karls-Universität
2009
PhD-Thesis
http://edoc.mpg.de/395207
oai:edoc.mpg.de:3956722008-12-1137:954
Muonic Atoms in Super-Intense Laser Fields
Shahbaz, Atif
expertsonly
Nuclear effects in hydrogenlike muonic atoms exposed to intense high-frequency laser fields have been studied. Systems of low nuclear charge number are considered where a nonrelativistic description applies. By comparing the radiative response for different isotopes we demonstrate characteristic signatures of the finite nuclear mass, size and shape in the high-harmonic spectra. Cutoff energies in the MeV domain can be achieved, offering prospects for the generation of ultrashort coherent γ-ray pulses. Also, the nucleus can be excited while the laser-driven muon moves periodically across it. The nuclear transition is caused by the time-dependent Coulomb field of the oscillating charge density of the bound muon. A closed-form analytical expression for electric multipole transitions is derived within a fully quantum mechanical approach and applied to various isotopes. The excitation probabilities are in general very small. We compare the process with other nuclear excitation mechanisms through coupling with atomic shells and discuss the prospects to observe it in experiment.
Ruprecht-Karls-Universität
2009
PhD-Thesis
http://edoc.mpg.de/395672
oai:edoc.mpg.de:4347172009-08-2137:954
Laser-induced high-energy processes in atomic, nuclear, and particle physics
Müller, Carsten
expertsonly
Ruprecht-Karls Universität
2009
Habilitation
http://edoc.mpg.de/434717
en
oai:edoc.mpg.de:4355192009-09-0437:954
Numerical studies of pair creation in counterpropagating laser fields
Ruf, Matthias
expertsonly
Pair creation from vacuum induced by electromagnetic fields is probably one of the most intriguing phenomena in physics. If the fields are sufficiently strong, the QED vacuum become unstable. Due to the remarkable progress inm laser technology during recent years an experimental investigation of pair creation by pure laser light is coming into reach. The focus of this thesis is on pair creation in counterpropagating laser beams. The pair creation probability is calculated employing the numerically obtained solutions of the Dirac equation. This numerical ansatz has the capability of calculating the momentum distribution of the created pairs in a single propagation, for pure time dependent field configurations. Furthermore, it allows to take the magnetic component of the laser fields into account, which is usually neglected. The latter strongly affects the creation process at high laser frequency. The involved numerical calculations are rather time consuming, therefore the second project of this thesis was to develop a highly efficient code for solving relativistic quantum mechanical problems. This is accomplished by adopting the split-operator method to the Klein-Gordon equation. Here the possibility arises to use parallel computing. However the corresponding spin-statistics becomes crucial in the case of pair creation, demonstrated in several examples.
Ruprecht-Karls Universität
2009
PhD-Thesis
http://edoc.mpg.de/435519
en
oai:edoc.mpg.de:4356032011-01-1437:954
Time-Dependent Density Functional Theory for Intense Laser-Matter Interaction
Ruggenthaler, Michael
expertsonly
In order to properly describe the dynamics of a many-particle system in strong, timedependent fields, a nonperturbative treatment of all constituents and of their correlation is needed. An ab initio solution of the time-dependent many-body Schr¨odinger equation is only feasible for simple systems. Hence, for many-electron systems in intense laser fields practicable methods for solving the quantum-mechanical many-body problem are required. An formally exact approach is the time-dependent density functional theory. In this work a mathematically rigorous formulation of the foundations of this theory is given. Further the non-locality in time of the exchange correlation functionals is examined, and we formally define the notion of “quantum memory”. We investigate the fundamental process of Rabi oscillations from a density functional point of view and find the few-level approximation to be in conflict with the basis of time-dependent density functional theory. Finally, we apply the theory to calculate the electron dynamics of C60 in intense laser pulses. Although the laser light is far off-resonant with respect to the collective modes of the C60 the multi-electron dynamics strongly influences the harmonic spectra. The efficiency of this multi-particle recollision process with respect to the usual single active electron approximation of high-order harmonic generation is estimated by two analytical models.
Ruprecht-Karls Universität
2009
PhD-Thesis
http://edoc.mpg.de/435603
en
oai:edoc.mpg.de:4758812010-05-1137:954
Light propagation in dense and chiral media
Fleischhaker, Robert
expertsonly
In quantum optics, the electromagnetic character of light is mostly reduced to its electric component. Technologically interesting, a medium interacting with both the electric and magnetic component has recently been proposed. But the suggested combination of high density and induced chirality to enhance the magnetic response is beyond the limits of current experiments. This thesis studies light propagation in dense and chiral media, assessing both concepts separately and in more accessible parameter ranges. In this context, we analyze a so-called closed-loop system, demonstrate a scheme for group velocity control in the UV range, show how to utilize parametric processes for light propagation, and explain effects due to high density on a slow light pulse. We derive the wave equation for media with induced chirality and solve it on the level of general medium response coefficients. This is then followed by a specific example, in which the developed concepts are applied to study light propagation with chiral interactions. We find that a chiral medium is an ideal implementation of a closed-loop-phase control scheme and show that the dynamics of a slow light pulse can be controlled throughout propagation time. Furthermore, our results demonstrate that the magnetic probe field component can become relevant for parameters achievable in current experiments.
Ruprecht-Karls Universität
2009
PhD-Thesis
http://edoc.mpg.de/475881
en
oai:edoc.mpg.de:5220492010-12-2037:954
Strong-field relativistic processes in highly chargerd ions
Postavaru, Octavian
expertsonly
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 Diracv 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.
Ruprecht-Karls-Universität
2010
PhD-Thesis
http://edoc.mpg.de/522049
en
oai:edoc.mpg.de:5238632011-01-1337:954
Vacuum polarisation effects in intense laser fields
King, Benjamin J.
expertsonly
Polarisation of the vacuum by an external electromagnetic field is predicted to lead to an array of non-linear processes. In light of upcoming laser facilities that will access intensity ranges orders of magnitude above current limits, the continued study of vacuum polarisation effects is both necessary and timely. By considering how photons from a probe laser field are scattered by two ultra-intense laser beams, we present a novel experimental scenario in which interference effects separate the vacuum signal from the probe background. By placing emphasis on experimental considerations, we demonstrate a realistic arrangement that could be used to observe, for the first time, real, elastic, photon-photon collisions. In doing so, we also show how strong-field lasers can in principle be used to generate a double-slit experiment consisting entirely of light. Moreover, such a set-up is also shown to modestly increase vacuum birefringence and dichroism over traditional two-beam collisions. We complement this by expounding an original theoretical method that incorporates both finite temperature and vacuum polarisation in a common setting. By employing this method on the case of a constant crossed field, we calculate the resulting change in the pressure of the vacuum in an external field.
Ruprecht-Karls-Universität
2010
PhD-Thesis
http://edoc.mpg.de/523863
en
oai:edoc.mpg.de:5238662011-01-1337:954
Multiphoton COMPTON scattering in ultra-short laser pulses
Mackenroth, Kai Felix
expertsonly
This work is dedicated to the computation of emission spectra of an electron scattering off an ultra-short and highly intense laser pulse. By ultra-short we label pulses containing only a single cycle of the laser's electric eld. To be able to describe highly intense laser elds we compute the emission spectra in the so called Furry picture of quantum dynamics taking an external electromagnetic eld into account exactly. For weak and ultra-strong incident laser pulses we will present analytical expressions for the emission spectra. For intermediate laser intensities we are going to present numerically computed spectra. Finally we are going to investigate the in uence of a changed carrier-envelope phase on the emission spectra. The main results of this work concern the observation of distinct differences in electron scattering between an ultra-short and a long laser pulse what has been investigated in the literature so far. Furthermore we note that the results of this work indicate the possibility to infer the carrier-envelope-phase from the angular distribution of the scattered photons.
Ruprecht-Karls-Universität
2009
Thesis
http://edoc.mpg.de/523866
en
oai:edoc.mpg.de:5258372011-01-2037:954
Elektron–Positron–Paarerzeugung durch Multiphotonen–Absorption im Stoß eines relativistischen Myons mit einem hochfrequenten Laserstrahl
Müller, Sarah
expertsonly
In the present work, electron–positron pair creation in the collision of a relativistic muon with a circular–polarised X–ray laser beam is investigated within the range of small laser intensity parameters. In the head–on collision between the muon projectile and the laser field, pairs of electrons and positrons are produced via the simultaneous absorption of one or more laser photons. The leading–order Feynman diagram of this process is evaluated within the framework of laser–dressed quantum electrodynamics employing relativistic Volkov states. The result is compared to the known expression for proton projectiles which are treated as external Coulomb field. In the limit of small laser intensity, both approaches are shown to coincide. Differential pair creation rates, in particular the recoil distribution, are calculated numerically. The dependence of the recoil effect on the projectile mass is discussed. We consider both linear and non–linear processes. Furthermore, we investigate the pair creation rate for proton projectiles in the above–threshold regime and find an exponential relation between the total rate and the ratio of electron rest mass to photon energy.
Ruprecht-Karls-Universität
2009
Thesis
http://edoc.mpg.de/525837
de
oai:edoc.mpg.de:5258392011-01-2037:954
Spin-Eff ekte bei der Multiphotonen-Paarerzeugung
Müller, Tim-Oliver
expertsonly
The thesis at hand deals with the influence of the lepton spin on the rates for e+e- pair production by a nucleus in an intense laser eld. The process of pair production is considered to be a Coulomb-induced transition from a Volkov state with negative energy to a Volkov state with positive energy, according to the Dirac theory. Starting with the transition amplitude for this process the pair production rates are calculated, taking di erent numbers of absorbed photons from a circularly polarized laser wave into account. Our calculations reproduce the well-known results for the spin-resolved single photon process.Beyond that we discover that the e ffect arising from polarization of the produced particles is not necessarily increased by absorbing more photons. In fact the energy transfer to the produced particles is identi ed as the main impact on their polarization. An efficient transfer of helicity becomes possible in the transition regime. Results for total and differential rates are going to be presented. The results for the considered processes are discussed with respect to the possibility of their experimental implementation.
Ruprecht-Karls-Universität
2009
Thesis
http://edoc.mpg.de/525839
de
oai:edoc.mpg.de:5283362011-01-2737:954
Measurement of Distance and Orientation of Two Atoms in Arbitrary Geometry
Gulfam, Qurrat-ul-Ain
expertsonly
Accurate measurement of relative distance and orientation of two nearby quantum particles is discussed. We are in particular interested in a realistic description requiring as little prior knowledge about the system as possible. Thus, unlike in previous studies, we consider the case of an arbitrary relative orientation of the two atoms. For this, we model the atom with complete Zeeman manifolds, and include parallel as well as orthogonal dipole-dipole couplings between all states of the two atoms. We find that it is possible to determine the distance of the two atoms independent of the orientation, as long as the particles are sufficiently close to each other. Next, we discuss how in addition the alignment of the atoms can be measured. For this, we focus on the two cases of atoms in a two-dimensional waveguide and of atoms on a surface. 2. We propose a scheme for the quantum teleportation of a generalized bipartite (N + 1)2 dimensional entangled field state in two high-Q cavities. All the processes of teleportation including preparation of entangled states in high-Q cavities, measurement of the basis.
Ruprecht-Karls-Universität
2009
Thesis
http://edoc.mpg.de/528336
en