Electron-photon Interaction Research Articles

Relativistic exchange energies for heavy atoms

We present the results of self-consistent calculations for the exchange and total energies for several heavy atoms based on the local relativistic density functional theory. Our calculations clearly demonstrate the importance of transverse photon-electron interaction to the exchange processes. The calculated total energies for all the atoms agree extremely well with that of the nonlocal Dirac-Fock calculations. It is found that the exchange energy is proportional to Z1.6. The commonly used nonrelativistic Slater Xα exchange potential in the Dirac equation overestimates the exchange contribution to the total energy.

Exciton-cyclotron resonance in two-dimensional structures in a strong perpendicular magnetic field and optical orientation conditions

The absorption band shapes of the combined optical quantum transitions with creation of the two-dimensional magnetoexcitons and simultaneous excitation of one background electron from its lowest to the first-excited Landau level by circularly polarized radiation under the conditions of optical orientation and spin polarization are investigated. The light absorption in the frame of dipole-active transition is described in the second-order perturbation theory taking into account as the perturbations the electron-photon interaction and the electron-electron Coulomb interaction. The Hamiltonian of the electron-photon interaction depends on the directions of the light propagation and its circular polarization relative to the magnetic field direction and the electron-heavy-hole alignment with regard to the plane of the layer. It is shown that the probability of the combined absorption rate is four times larger if the optically created electron has the same spin projection as the background electrons, compared to the case when the electrons have antiparallel spins. The probability of quantum transition and the absorption band peaks decrease with the increased magnetic field as H-1/2 at a given filling factor v(2). If photocreated electron and hole have the same numbers of the Landau levels, n(e)=n(h), the quantum transitions are dipole active. If these numbers differ by one, the quantum transition is quadrupole active, depends on the projections of the light wave vector on the plane of the layer, and vanishes in the Faraday geometry.

Photon polarization in the two-photon decay of heavy hydrogen-like ions

We have applied the density matrix and second-order perturbation theory in order to re-analyze the two-photon decay of hydrogen-like ions for the polarization of emitted light. Special attention is paid to the linear polarization of one of the photons, while the spin state of the second photon is supposed to be unobserved. For such an “angle-polarization” correlation of the two photons we investigate the contributions that arise from non electric-dipole terms in the expansion of the electron-photon interaction. Detailed calculations are performed for the 2s1/2 →1s1/2 and 3d5/2 →1s1/2 transitions in neutral hydrogen as well as in hydrogen-like uranium.

Photon transparency in metallic photonic crystals doped with an ensemble of nanoparticles

Quantum optics of metallic photonic crystals is studied in this paper. Crystals are made from metallic spheres and a background dielectric material. The refractive index of the metallic spheres depends on the frequencies of the incident light and plasmons whereas the refractive index of the background material is a constant. Crystals are lightly doped with four-level nanoparticles. It is considered that nanoparticles are interacting with the metallic crystals via electron-photon interaction in the dipole approximation. The probe and pump laser fields are applied to monitor the absorption spectrum in the system. Two transparent states are predicted. One is due to the electromagnetically induced transparency and the other is due to the electron-photon interaction. For certain experimental conditions these transparent states merge into one transparent state. The effect of plasmon frequencies has also been studied. It is found that the system can be switched from a transparent state to an absorbing state just by changing the frequency of plasmons. This study can be used to makes new types of optical devices such as switches and optical transistors.

A semiclassical approach for the phase matching effect in the nonlinear optical phenomena

In this paper we present a semiclassical model for explanation of the nonlinear optical effect and phase matching. We calculate momentary quantities of the delay time of photon–electron interaction in each layer. We show that for phase matching, the average delay time for the fundamental photons must be equal to the average delay time for the harmonic photons. Additionally, we calculate the number of layers that the harmonic photon needs to be absorbed or converted to fundamental photons. This calculation applies to different wavelengths with different phase matching angles. Our simulation results are in good agreement with experimental data.

IONIZATION BY QUANTIZED ELECTROMAGNETIC FIELDS: THE PHOTOELECTRIC EFFECT

In this paper, we explain the photoelectric effect in a variant of the standard model of non relativistic quantum electrodynamics, which is in some aspects more closely related to the physical picture, than the one studied in [5]. Now, we can apply our results to an electron with more than one bound state and to a larger class of electron-photon interactions. We will specify a situation, where the second order of ionization probability is a weighted sum of single photon terms. Furthermore, we will see that Einstein's equality [Formula: see text] for the maximal kinetic energy E kin of the electron, energy hν of the photon and ionization gap △E is the crucial condition, for these single photon terms to be nonzero.

Microscopic nonequilibrium theory of quantum well solar cells

We present a microscopic theory of bipolar quantum well structures in the photovoltaic regime, based on the non-equilibrium Green's function formalism for a multi band tight binding Hamiltonian. The quantum kinetic equations for the single particle Green's functions of electrons and holes are self-consistently coupled to Poisson's equation, including inter-carrier scattering on the Hartree level. Relaxation and broadening mechanisms are considered by the inclusion of acoustic and optical electron-phonon interaction in a self consistent Born approximation of the scattering self energies. Photogeneration of carriers is described on the same level in terms of a self energy derived from the standard dipole approximation of the electron-photon interaction. Results from a simple two band model are shown for the local density of states, spectral response, current spectrum, and current-voltage characteristics for generic single quantum well systems.

Photon equation of motion with application to the electron’s anomalous magnetic moment

The photon equation of motion previously applied to the Lamb shift is here applied to the anomalous magnetic moment of the electron. Exact agreement is obtained with the QED result of Schwinger. The photon theory treats the radiative correction to the photon in the presence of the electron rather than its inverse as in standard QED. The result is found to be first order in the photon–electron interaction rather than second order as in standard QED, introducing an ease of calculation hitherto unavailable.

Electron-photon interaction associated with uncertainty-based tunneling in a parallel double quantum dot

The electron-photon interaction associated with the uncertainty based tunneling (EPAUT) in the parallel double quantum dot system is studied. In the considered system, the electron interacts with the single mode detuning quantum photon field, i.e., ${\ensuremath{\omega}}_{\mathit{ph}}+\ensuremath{\Delta}={\ensuremath{\epsilon}}_{2}\ensuremath{-}{\ensuremath{\epsilon}}_{1}$, and transits between the quantum dots (QDs). The corresponding characteristic temperature is calculated and compared with the Kondo temperature to recognize the role of the related quantities. There are two energy uncertainties in the considered system. One is the energy difference between the energy of electron-photon interacting quasiparticle and the Fermi energy of the lead. The other is the detuning factor $\ensuremath{\Delta}$. Besides, $\ensuremath{\mid}\ensuremath{\Delta}∕\ensuremath{\pi}\ensuremath{\mid}$ is the bandwidth of the intermediate state of EPAUT. The peak of the density of state corresponding to the EPAUT rises when the temperature is in the order of or below the characteristic temperature. The EPAUT peak can be modified via tuning the Fermi energy of the lead connected to the adjoined QD. Hence, the conductance between the connected leads is varied via tuning the Fermi energy of the lead connected to the adjoined QD.

Temperature Dependence of Abnormal Fano Resonance in Photon-Assisted Transport Through a Side-Coupled Quantum Dot

We investigate transport through a perfect quantum wire with a side-coupled quantum dot under an ac field. Time-averaged complex conductance is formulated by using the nonequilibrium Green function (NGF) method. We find that the electron-photon interaction together with the quantum interference of electron wave function can lead to anti-resonance in the conductance, which is then useful for tuning coherence and phases of electrons. Meanwhile, we study the temperature dependence of the conductance. Interestingly, a peak-structure can be developed at the Fano resonance levels with increasing temperatures.

Analysis of Surface Texturization of Solar Cells by Molecular Dynamics Simulations

The purpose of this paper is to develop a simple new model, based on the classic molecular dynamics simulation (MD), alternative to complex electron-photon interactions to analyze the surface texturization of solar cells. This methodology can easily propose the absorptance differences between texturing and nontexturing solar cells. To verify model feasibility, this study simulates square, pyramidal, and semicircular texturization surfaces. Simulations show that surface texturization effectively increases the absorptance of incident light for solar cells, and this paper presents optimal texturization shapes. The MD model can also be potentially used to predict the efficiency promotion in any optical reflection-absorption cases.

Analysis of Pyramidal Surface Texturization of Silicon Solar Cells by Molecular Dynamics Simulations

The purpose of this paper is to explore the relations between surface texturization and absorptance of multicrystalline silicon solar cells by a simple new model, based on the classic molecular (MD) dynamics simulation, alternative to complex electron-photon interactions to analyze the surface texturization of solar cells. In this study, the large tilted angle leads to the lower efficiency of solar cell. To consider the effect of incident angle, a range of high efficiency exists due to the increasing probability of second reflection. Furthermore, the azimuth angle of incident light also affects the efficiency of solar cells. Our results agree well with previous studies. This MD model can potentially be used to predict the efficiency promotion in any optical reflection-absorption cases.

Broadband magneto-optical absorption by a Rashba spintronic system

We examine the selection rules for electron-photon interaction in a two-dimensional electron gas (2DEG) in the presence of the Rashba spin-orbit interaction and quantizing magnetic fields. In such a case, new channels open up for electronic transition accompanied by the absorption of photons. As a result, two absorption peaks and a broadband absorption spectrum can be observed for high-mobility samples at relatively high magnetic fields. We find that electronic transitions between the neighboring Landau levels within the same spin orientation are the main channels for magneto-optical absorption in a spin-split 2DEG.

Convergent close coupling calculations of two-photon double ionization of He

We review recent applications of the convergent close-coupling (CCC) method to studies of two-photon double ionization (TPDI) of He. In a weak-field regime, the electron-photon interaction can be treated within the lowest order perturbation theory (LOPT) whereas the electron-electron interaction is included in full. The intermediate states of the target can either be represented by a discrete set of B-splines in a box or summed over with an average weight (closure approximation). In a non-perturbative regime, we solve the time-dependent Schrödinger equation on a square-integrable basis and project this solution on a set of CCC final states. In both regimes, we are able to calculate reliably the total intgrated and full differential TPDI cross-sections.Besides purely numerical results, we introduce a convenient analytical parametrization of the TPDI amplitude in the manner similar to single photon double ionization. Aided with this parametrization, we observe two distinctly different modes of correlated motion of the photoelectron pair. We also derive the angular anisotropy parameters and the recoil ion momentum distribution for TPDI of He. The latter can be compared with recent experimental observations.

Broadband optical absorption in a two-dimensional electron gas in the presence of spin–orbit interaction and high magnetic fields

We examine the selection rules for electron–photon interaction in a two-dimensional electron gas (2DEG) in the presence of the Rashba spin–orbit interaction (RSOI) and quantizing magnetic fields. In such a case, new channels open up for electronic transition accompanied by the absorption of photons. As a result, two absorption peaks and a broadband absorption spectrum can be observed for high-mobility samples at relatively high magnetic fields. We find that electronic transitions between the neighboring Landau levels within the same spin orientation are the main channels for optical absorption in a spin–split 2DEG.

Theory of x-ray absorption by laser-dressed atoms

An ab initio theory is devised for the x-ray photoabsorption cross section of atoms in the field of a moderately intense optical laser (800nm, 10^13 W/cm^2). The laser dresses the core-excited atomic states, which introduces a dependence of the cross section on the angle between the polarization vectors of the two linearly polarized radiation sources. We use the Hartree-Fock-Slater approximation to describe the atomic many-particle problem in conjunction with a nonrelativistic quantum-electrodynamic approach to treat the photon-electron interaction. The continuum wave functions of ejected electrons are treated with a complex absorbing potential that is derived from smooth exterior complex scaling. The solution to the two-color (x-ray plus laser) problem is discussed in terms of a direct diagonalization of the complex symmetric matrix representation of the Hamiltonian. Alternative treatments with time-independent and time-dependent non-Hermitian perturbation theories are presented that exploit the weak interaction strength between x rays and atoms. We apply the theory to study the photoabsorption cross section of krypton atoms near the K edge. A pronounced modification of the cross section is found in the presence of the optical laser.

OBSERVATION OF NONLINEAR THOMSON SCATTERING AT BNL-ATF

Measurement of X-rays produced in nonlinear Thomson scattering of high power laser and electron beams is a good test of electrodynamics in the high field region. We performed an experiment of head-on collision between sub-terawatt CO 2 laser and 60-MeV electron beams at Brookhaven National Laboratory, Accelerator Test Facility. Angular distributions of X-rays produced in Thomson scattering were measured and contribution of the second order nonlinear interaction was observed by comparing the distributions with Monte Carlo simulations based on the semi-classical theory of photon-electron interactions.

SOME ASPECTS OF THE ELECTRON-BOSON INTERACTION AND OF THE ELECTRON-ELECTRON INTERACTION VIA BOSONS

By using a Hamiltonian of interaction between fermions via bosons1 we derive some properties of the electro-phonon and electron-photon interaction and also of the electron-electron interaction. We have obtained that in a degenerate electron gas there is an attraction between two electrons via acoustical phonons. Also, in certain conditions, there may be an attraction between two electrons via longitudinal optical phonons. Although our expressions for the polaron energy in both cases of the acoustical and longitudinal optical phonons are different from that obtained in the standard theory, their magnitudes are the same with these and they are in good agreement with experimental data. The total emission rate of an electron against a phonon system at absolute zero is directly proportional to the electron momentum. Also, an attraction between two electrons may appear via photons.

A new algorithm for accurate evaluation of the generalized Bloch–Gruneisen function and its applications to MgB2 superconductor

The objective of this Letter is to provide an efficient and reliable analytical procedure for the generalized Bloch–Gruneisen function with the Debye temperatures for the wide temperature range using the binomial expansion theorems. As will be seen, the present formulation yields compact closed-form expressions which enable the ready calculation of Bloch–Gruneisen function for integer and noninteger values of parameter m. The proposed procedure guarantees the reliable application of the contribution of electron–photon interaction to the electrical resistivity of metals. Finally, the algorithm is used to simulate the variation of the resistivity and thermal conductivity against temperature sintered polycrystalline MgB2. Furthermore, the comparison of the method with numerical calculations demonstrates the applicability and accuracy of the method.

Convergent close-coupling calculations of two-photon double ionization of helium

We apply the convergent close-coupling (CCC) formalism to the problem of two-photon double ionization of helium. The electron–photon interaction is treated perturbatively whereas the electron–electron interaction is included in full. The integrated two-photon double ionization cross-section is substantially below non-perturbative literature results. However, the pattern of the angular correlation in the two-electron continuum is remarkably close to the non-perturbative time-dependent close-coupling calculation of Hu et al (2005 J. Phys. B: At. Mol. Opt. Phys. 38 L35).