64 research outputs found
The Off-Shell Electromagnetic T-matrix: momentum-dependent scattering from spherical inclusions with both dielectric and magnetic contrast
The momentum- and frequency-dependent T-matrix operator for the scattering of
electromagnetic waves by a dielectric/conducting and para- or diamagnetic
sphere is derived as a Mie-type series, and presented in a compact form
emphasizing various symmetry properties, notably the unitarity identity. This
result extends to magnetic properties one previously obtained for purely
dielectric contrasts by other authors. Several situations useful to
spatially-dispersive effective-medium approximations to one-body order are
examined. Partial summation of the Mie series is achieved in the case of
elastic scattering.Comment: 22 pages. Preprint of a paper to appear in `Waves in Complex And
Random Media' ((c) Taylor and Francis, 2011
Selective scattering between Floquet-Bloch and Volkov states in a topological insulator
The coherent optical manipulation of solids is emerging as a promising way to
engineer novel quantum states of matter. The strong time periodic potential of
intense laser light can be used to generate hybrid photon-electron states.
Interaction of light with Bloch states leads to Floquet-Bloch states which are
essential in realizing new photo-induced quantum phases. Similarly, dressing of
free electron states near the surface of a solid generates Volkov states which
are used to study non-linear optics in atoms and semiconductors. The
interaction of these two dynamic states with each other remains an open
experimental problem. Here we use Time and Angle Resolved Photoemission
Spectroscopy (Tr-ARPES) to selectively study the transition between these two
states on the surface of the topological insulator Bi2Se3. We find that the
coupling between the two strongly depends on the electron momentum, providing a
route to enhance or inhibit it. Moreover, by controlling the light polarization
we can negate Volkov states in order to generate pure Floquet-Bloch states.
This work establishes a systematic path for the coherent manipulation of solids
via light-matter interaction.Comment: 21 pages, 6 figures, final version to appear in Nature Physic
Electron-impact Excitation of Atoms in the Presence of a Nearly Resonant Laser Field
We have studied the electron-impact excitation of an atom, in the presence of a laser field whose photon energy is tuned close to the energy difference between two excited final states. Both the laser-projectile and the laser-target interactions are treated nonperturbatively, while the electron-atom interaction is treated within the first Born approximation. As an application, we have analyzed the resonant laser-assisted excitation of the 21S and 21P states of helium. The agreement between the present nonperturbative results and previous perturbative ones is excellent, except for very small detunings. The present nonperturbative treatment also shows that the results given by perturbation theory on both sides of the resonance, when plotted as a function of the laser frequency, correspond to the excitation of different Floquet pseudostates. This is related to the presence of avoided crossings in the diagram of the Floquet pseudoenergies, as a function of the laser frequency. © 1990 The American Physical Society.SCOPUS: ar.jinfo:eu-repo/semantics/publishe
Pre-gaussian Model of Laser Noise - Application To Resonant 2-photon Ionization
We present a theoretical treatment of resonant two-photon ionization in the presence of a noisy laser. The atom is modeled by a two-level system, while the statistical fluctuations of the field are described within the framework of the pre-Gaussian model. We show that previous results obtained by using Ornstein-Uhlenbeck statistics are recovered in the appropriate limit in the case of frequency fluctuations. We also give new results in the case of phase and amplitude noise. © 1987 The American Physical Society.SCOPUS: ar.jinfo:eu-repo/semantics/publishe
A 3rd-order Optical-potential Theory for Elastic-scattering of Electrons and Positrons By Atomic-hydrogen
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