Madalina Boca
@unibuc.ro
Faculty of Physics
University of Bucharest
RESEARCH INTERESTS
Theoretical Physics
Scopus Publications
Scholar Citations
Scholar h-index
Scholar i10-index
Scopus Publications
Petru-Vlad Toma, Sebastian Micluţa-Câmpeanu, Mădălina Boca, Alexandru Nicolin, and Virgil Băran
AIP Publishing
Madalina Boca
Author(s)
We study the scattering of intense electromagnetic radiation on free relativistic electrons in the classical formalism. Starting from the well known property that in the relativistic regime the radiation is emitted by an accelerated charged particle along its instantaneous velocity direction we discuss the effects of the radiation reaction on the shape of the angular distribution in Thomson effect for the case of linear and circular polarization of the incident light and for different collision geometries. We also study the polarization properties of the emitted radiation for several low intensity cases.
M Boca, C Stoica, A Dumitriu, and V Florescu
IOP Publishing
We study in the framework of quantum electrodynamics the scattering of a plane wave electromagnetic field on free electrons in the low intensity limit. We derive analytic formulas describing the polarization properties of the emitted photons. We discuss and illustrate with a numerical example the effects of the electromagnetic pulse duration on their polarization.
Madalina Boca
Walter de Gruyter GmbH
AbstractWe study the Mott scattering of charged spinless particles in the presence of an intense plane wave laser pulse with fixed propagation direction and arbitrary duration and shape. We derive two equivalent forms of the transition amplitude and we discuss the relation between the respective results obtained in the case of a laser pulse and the monochromatic case. We obtain the condition defining the boundaries of the “bright” domain (the domain of allowed values in the energy-direction space of the scattered particle) and we illustrate our results with numerical examples.
Madalina Boca, Victor Dinu, and Viorica Florescu
American Physical Society (APS)
Madalina Boca, Victor Dinu, and Viorica Florescu
Elsevier BV
Madalina Boca, Viorica Florescu, and Mihai Gavrila
American Physical Society (APS)
We obtain a generalization of the nonrelativistic space-translation transformation to the Dirac equation in the case of a unidirectional laser pulse. This is achieved in a quantum-mechanical representation connected to the standard Dirac representation by a unitary operator T transforming the Foldy-Wouthuysen free-particle basis into the Volkov spinor basis. We show that a solution of the transformed Dirac equation containing initially low momenta p (p/mc 1) will maintain this property at all times, no matter how intense the field or how rapidly it varies (within present experimental capabilities). As a consequence, the transformed four-component equation propagates independently electron and positron wave packets, and in fact the latter are propagated via two two-component Pauli equations, one for the electron, the other for the positron. These we shall denote as the Pauli low-momentum regime (LMR) equations, equivalent to the Dirac equation for the laser field. Successive levels of dynamical accuracy appear depending on how accurately the operator T is approximated. At the level of accuracy considered in this paper, the Pauli LMR equations contain no spin matrices and are in fact two-component Schrodinger equations containing generalized time-dependent potentials. The effects of spin are nevertheless included in the theory because, in the calculation of observables which are formulated in the laboratory frame, use is made of the spin-dependent transformation operator T . In addition, the nonrelativistic limit of our results reproduces known results for the laboratory frame with spin included. We show that in intense laser pulses the generalized potentials can undergo extreme distortion from their unperturbed form. The Pauli LMR equation for the electron is applicable to one-electron atoms of small nuclear charge (αZ 1) interacting with lasers of all intensities and frequencies ω mc2.
Victor Dinu, Madalina Boca, and Viorica Florescu
IOP Publishing
Our calculation of the final electron distribution in nonlinear Compton scattering with very energetic electrons is performed for an electromagnetic pulse with finite duration. In contrast to the monochromatic case, this gives access to the the asymptotically free electrons and not to those dressed by the laser field.
Madalina Boca
IOP Publishing
We present an elementary proof based on a direct calculation of the property of completeness at constant time of the solutions of the Klein–Gordon equation for a charged particle in a plane wave electromagnetic field. We also review different forms of the orthogonality and completeness relations previously presented in the literature and discuss the possibility of constructing the Feynman propagator for the particle in a plane-wave laser pulse as an expansion in terms of Volkov solutions. We show that this leads to a rigorous justification for the expression of the transition amplitude, currently used in the literature, for a class of laser-assisted or laser-induced processes.
Madalina Boca and Andreea Oprea
IOP Publishing
Within the framework of classical electrodynamics, we investigate the scattering of a very intense laser pulse on ultrarelativistic electrons. The laser pulse is modeled by a plane wave of finite length. For a circularly polarized laser pulse, we focus on the angular distribution of the emitted radiation in its dependence on the electron energy for the cases of head-on and 90° collisions. We investigate the relation between dW/dΩ and the trajectory followed by the velocity of the electron during the laser pulse; for the case of a short laser pulse, we discuss the carrier–envelope phase effects. We also present an analysis of the polarization of emitted radiation. We present two scaling laws that allow us to predict the behavior of angular distributions for a broad range of parameters.
M. Boca and V. Florescu
Springer Science and Business Media LLC
Madalina Boca and Viorica Florescu
American Physical Society (APS)
A factor with the expression p0 2/(n · p2) is missing from the right-hand side of Eqs. (32), (34), and (38) and the numerical computations based on them. However, this factor differs by less than 10−5 from 1 for all the plots corresponding to an electron initially at rest, which stay, therefore, practically correct. The only figure to be amended is Fig. 4 since, for the very high initial electron momentum it corresponds, the factor is close to 0.5. The deviation from 0.5 being no bigger than 10−6, a simple division by 2 is enough to get the true values of σ (2) from the published ones in Fig. 4. Nevertheless, we present here the corrected Fig. 4. Furthermore, the phrase after Eq. (47) must be replaced by “In both cases it is obvious that the envelope has negligible values except for a finite duration, proportional to the parameter τ in the expression of the envelope, and, as a consequence, the factor τp (the effective pulse duration) used in Eq. (31) should be chosen proportional to τ ; we have taken τp = 2λτ .” The error was the omission of the factor 2 in the expression of τp. Our numerical calculation did include this factor.
G S J Armstrong, J S Parker, M Boca, and K T Taylor
IOP Publishing
We present high-accuracy calculations of ionization rates of helium at UV (195 nm) wavelengths. The numerical results are obtained from full-dimensional numerical integration of the two-electron time-dependent Schrödinger equation. Comparison is made between ionization rates at 195 nm with previously obtained data at 390 nm and 780 nm. In addition, we have obtained quantitatively accurate solutions of the full-dimensional time-dependent Schrödinger equation for static-field ionization of helium. We compare our numerically integrated rates with those of time-independent calculations, and obtain good agreement over a wide range of intensities.
Madalina Boca and Viorica Florescu
IOP Publishing
We theoretically investigate the scattering of intense laser radiation on energetic electrons. The laser field is described as a pulse with a fixed propagation direction; this allows the use of relativistic Volkov solutions and leads to a transition amplitude which is a product of a three-dimensional δ-function with an one-dimensional integral evaluated numerically. We study the dependence of the emitted photon spectrum on the pulse duration. In contrast with the monochromatic case, where the spectrum is discrete, in our case one obtains a continuous distribution with a succession of maxima located near the corresponding discrete values.
J S Parker, G S J Armstrong, M Boca, and K T Taylor
IOP Publishing
We present high-accuracy calculations of ionization rates of helium at UV (195 nm) wavelengths. The data are obtained from full-dimensionality integrations of the helium-laser time-dependent Schrödinger equation. Comparison is made with our previously obtained data at 390 nm and 780 nm. We show that scaling laws introduced by Parker et al extend unmodified from the near-infrared limit into the UV limit. Static-field ionization rates of helium are also obtained, again from time-dependent full-dimensionality integrations of the helium Schrödinger equation. We compare the static-field ionization results with those of Scrinzi et al and Themelis et al, who also treat the full-dimensional helium atom, but with time-independent methods. Good agreement is obtained.
Madalina Boca and Viorica Florescu
American Physical Society (APS)
We investigate the scattering of intense laser radiation on free electrons using a semiclassical relativistic approach. The laser field is described as an ideal pulse with a finite duration, a fixed direction of propagation, and indefinitely extended in the plane perpendicular to it. This allows the use of Volkov solutions and leads to a transition amplitude which is a product of a three-dimensional delta function with a linear combination of three one-dimensional integrals that we evaluate numerically. We give the general expression of the emitted photon spectrum as a function of frequency and direction valid for any initial geometry of the electron-laser beam scattering and for arbitrary shape, duration, and polarization of the laser pulse averaged over the initial electron spin and summed over the emitted photon and ejected electron polarizations. At a fixed photon scattering angle, one obtains a continuous frequency distribution with a succession of maxima located near the discrete values corresponding to the monochromatic case. We present results for head-on collisions and circularly polarized laser pulses. Our figures illustrate the dependence of the photon spectrum on pulse parameters (duration, shape, and maximum intensity) and the role of the initial electron energy. For a few-cycle linearly polarized pulse we also explore the effect of the carrier-envelope phase.
Mădălina Boca, Iulia Ghiu, Paulina Marian, and Tudor A. Marian
American Physical Society (APS)
Centre for Advanced Quantum Physics, University of Bucharest,P.O.Box MG-11, R-077125 Bucharest-M˘agurele, Romania(Dated: June 30, 2009)We evaluate a Gaussian distance-type degree of nonclassicality for a single-mode Gaussian state ofthe quantum radiation field by use of the recently discovered quantum Chernoff bound. The generalproperties of the quantum Chernoff overlap and its relation to the Uhlmann fidelity are interestinglyillustrated by our approach.
M. Boca and V. Florescu
Springer Science and Business Media LLC
Marius Stroe and Mãdãlina Boca
American Physical Society (APS)
We report discrepancies between the results presented in Fig. 1 of a recent paper of Yasuike and Someda [Phys. Rev. A66, 053410 (2002)] and our independent calculation. At the frequency $\\ensuremath{\\omega}=0.55\\phantom{\\rule{0.3em}{0ex}}\\mathrm{a.u.}$, we find that the state of the one-dimensional modified P\\"oschl-Teller potential, described by the authors as light induced and originating from a shadow of the field-free ground state, is in fact physical for ${\\ensuremath{\\alpha}}_{0}l10\\phantom{\\rule{0.3em}{0ex}}\\mathrm{a.u.}$ and its origin is the zero-energy antibound state of the bare potential. For $\\ensuremath{\\omega}=0.45\\phantom{\\rule{0.3em}{0ex}}\\mathrm{a.u.}$, we also find differences in one of the presented quasienergy trajectories in the low ${\\ensuremath{\\alpha}}_{0}$ region $({\\ensuremath{\\alpha}}_{0}l0.4\\phantom{\\rule{0.3em}{0ex}}\\mathrm{a.u.})$, but we confirm the starting point at $E=\\ensuremath{-}0.5\\phantom{\\rule{0.3em}{0ex}}\\mathrm{a.u.}$ for both quasienergies, as found by Yasuike and Someda.
M Boca, H G Muller, and M Gavrila
IOP Publishing
We present a comprehensive calculation of 3D dynamic stabilization (DS) of ground-state hydrogen in superintense circularly polarized laser pulses. Three laser-pulse envelopes have been considered: Gaussian, sech, and Lorentzian. The ionization probability at the end of the pulse Pion was calculated for a range of high frequencies ω ranging from 0.65 to 8 au, for peak fields up to about 60 au (depending on ω), and for full width at half maximum pulse lengths τp extending from 0.25 to 100 cycles (depending on ω). This is a very accurate calculation, very much more time consuming than its linear polarization counterpart. For Gaussian and sech pulses we find prominent DS and substantial atomic survival under conditions where our nonrelativistic, dipole approximation calculation is expected to be valid. For Lorentzian pulses there is no DS in the range studied, and we explain the reasons. We find that the evolution of the atom is adiabatic and amenable to single-state Floquet theory, up to very large peak fields (several au), and down to very short pulses (few cycle, subfemtosecond). The general case of nonadiabatic pulses is interpreted in terms of the multistate Floquet theory. We compare the results for Pion in the cases of circular and linear polarization and find a surprising resemblance, when represented as a function of the peak intensity. Our results indicate the possibility of observing DS experimentally with the VUV–FEL light sources that are now in test operation, or with the attosecond pulses obtained from high harmonic generation, in a state-of-the-art experiment, however.
C. Chiril�, M. Boca, V. Dinu, and V. Florescu
Springer Science and Business Media LLC
Mãdãlina Boca, Ciprian Chirilã, Marius Stroe, and Viorica Florescu
Elsevier BV