Formulation of the twisted-light–matter interaction at the phase singularity: The twisted-light gauge

Twisted light is light carrying orbital angular momentum. The profile of such a beam is a ring-like structure with a node at the beam axis, where a phase singularity exists. Due to the strong spatial inhomogeneity the mathematical description of twisted-light–matter interaction is non-trivial, in particular close to the phase singularity, where the commonly used dipole-moment approximation cannot be applied. In this paper we show that, if the handedness of circular polarization and the orbital angular momentum of the twisted-light beam have the same sign, a Hamiltonian similar to the dipole-moment approximation can be derived. However, if the signs differ, in general the magnetic parts of the light beam become of significant importance and an interaction Hamiltonian which only accounts for electric fields is inappropriate. We discuss the consequences of these findings for twisted-light excitation of a semiconductor nanostructures, e.g., a quantum dot, placed at the phase singularity.Fil: Quinteiro, Guillermo Federico. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; ArgentinaFil: Kuhn, Tilmann. Westfalische Wilhelms Universitat; AlemaniaFil: Reiter, D. E.. Westfalische Wilhelms Universitat; Alemani

Light-hole transitions in quantum dots: Realizing full control by highly focused optical-vortex beams

An optical vortex is an inhomogeneous light beam having a phase singularity at its axis, where the intensity of the electric and/or magnetic field may vanish. Already well studied are the paraxial beams, which may carry well-defined values of spin (polarization σ) and orbital angular momenta; the orbital angular momentum per photon is given by the topological charge times the Planck constant. Here we study the light hole–to–conduction band transitions in a semiconductor quantum dot induced by a highly focused beam originating from a = 1 paraxial optical vortex. We find that at normal incidence the pulse will produce two distinct types of electron-hole pairs, depending on the relative signs of σ and . When sgn(σ) = sgn(), the pulse will create electron-hole pairs with band+spin and envelope angular momenta both equal to 1. In contrast, for sgn(σ) = sgn(), the electron-hole pairs will have neither band+spin nor envelope angular momenta. A tightly focused optical-vortex beam thus makes possible the creation of pairs that cannot be produced with plane waves at normal incidence. With the addition of co-propagating plane waves or switching techniques to change the charge both the band+spin and the envelope angular momenta of the pair wave function can be precisely controlled. We discuss possible applications in the field of spintronics that open up.Fil: Quinteiro, Guillermo Federico. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; Argentina. Universität Münster; AlemaniaFil: Kuhn, Tilmann. Universität Münster; Alemani

Diseño de un dispositivo compacto para generar y testear vórtices ópticos

Presentamos un diseño compacto para generar y testear diferentes vórtices ópticos con momento angular orbital (OAM). El diseño consiste en una máscara que contiene un holograma binario y un pinhole. Cuando la máscara es iluminada y el pinhole se bloquea el holograma produce un vórtice óptico con OAM cuya distribución de intensidades se observa en el campo lejano. Cuando se deja pasar la luz proveniente del pinhole se genera una onda de referencia que permite testear de manera interferométrica la distribución especial de fase del haz. Mostramos simulaciones numéricas del experimento para dos clases de haces conteniendo OAM: un haz tipo Laguerre-Gauss y un haz Mathieu.We present a compact design to generate and test different vortex beams with orbital angular momentum (OAM). The design consists of a mask that contains both, a binary amplitude hologram and a pinhole. When the mask is illuminated and the pinhole is blocked, the hologram produces a vortex beam with OAM whose intensity distribution can be observed in the far field. When the pinhole is unblocked a reference wavefront is generated which allows testing interferometrically the spatial phase distribution of the beam. We numerically simulate the experiment for two kind of beams containing OAM: Laguerre-Gaussian like vortex beams and Mathieu beams.Fil: Pabon Riaño, Dudbil Olvasada. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; ArgentinaFil: Ledesma, Silvia Adriana. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; ArgentinaFil: Quinteiro, Guillermo Federico. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; ArgentinaFil: Capeluto, Maria Gabriela. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; Argentin

Dark exciton preparation in a quantum dot by a longitudinal light field tuned to higher exciton states

Several important proposals to use semiconductor quantum dots in quantum information technology rely on the control of the dark exciton ground states, such as dark exciton based qubits with a microsecond lifetime. In this paper, we present an efficient way to occupy the dark exciton ground state by a single short laser pulse. The scheme is based on an optical excitation with a longitudinal field component featured by, e.g., radially polarized beams or certain Laguerre-Gauss or Bessel beams. Utilizing this component, we show within a configuration interaction approach that high-energy exciton states composed of light-hole excitons and higher dark heavy-hole excitons can be addressed. When the higher exciton relaxes, a dark exciton in its ground state is created.Fil: Holtkemper, M.. Westfälische Wilhelms Universität; AlemaniaFil: Quinteiro, Guillermo Federico. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Modelado e Innovación Tecnológica. Universidad Nacional del Nordeste. Facultad de Ciencias Exactas Naturales y Agrimensura. Instituto de Modelado e Innovación Tecnológica; ArgentinaFil: Reiter, Doris E.. Westfälische Wilhelms Universität; AlemaniaFil: Kuhn, Tilmann. Westfälische Wilhelms Universität; Alemani

Below-bandgap excitation of bulk semiconductors by twisted light

I theoretically investigate the excitation of bulk semiconductors by twisted light below the energy bandgap. To this end, I modify a well-known model of light-semiconductor interaction to account for the conservation of the momentum of light. I predict that the optical excitation produces a superposition of exciton-like states that undergo a complex center-of-mass motion. In addition, I show that the energy at which the absorption occurs is slightly different from that of pure excitons, due to the center-of-mass kinetic energy of the new states. Finally, I provide expressions for the induced polarization and electric current, which exhibit complex spatial patterns that mimic the twisted-light electric field. Copyright © 2010 EPLA.Fil: Quinteiro, Guillermo Federico. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; Argentin

Electric currents induced by twisted light in quantum rings

We theoretically investigate the generation of electric currents in quantum rings resulting from the optical excitation with twisted light. Our model describes the kinetics of electrons in a two-band model of a semiconductor-based mesoscopic quantum ring coupled to light having orbital angular momentum (twisted light). We find the analytical solution, which exhibits a circular photon-drag effect and an induced magnetization, suggesting that this system is the circular analog of that of a bulk semiconductor excited by plane waves. For realistic values of the electric field and material parameters, the computed electric current can be as large as juA; from an applied perspective, this opens new possibilities to the optical control of the magnetization in semiconductors. © 2009 Optical Society of America.Fil: Quinteiro, Guillermo Federico. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; ArgentinaFil: Berakdar, J.. Martin-universitat Halle-wittenberg; Alemani

Electronic transitions in disk-shaped quantum dots induced by twisted light

We theoretically investigate the absorption and emission of light carrying orbital angular momentum (twisted light) by quasi-two-dimensional (disk-shaped) quantum dots in the presence of a static magnetic field. We calculate the transition matrix element for the light-matter interaction and use it to explore different scenarios, depending on the initial and final states of the electron undergoing the optically induced transition. We make explicit the selection rule for the conservation of the z projection of the orbital angular momentum. For a realistic set of parameters (quantum dot size, beam waist, photon energy, etc.) the strength of the transition induced by twisted light is 10% of that induced by plane waves. Finally, our analysis indicates that it may be possible to select precisely the electronic level one wishes to populate using the appropriate combination of light-beam parameters suggesting technological applications to the quantum control of electronic states in quantum dots. © 2009 The American Physical Society.Fil: Quinteiro, Guillermo Federico. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; ArgentinaFil: Tamborenea, Pablo Ignacio. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; Argentin

Formulation of the twisted-light-matter interaction at the phase singularity: Beams with strong magnetic fields

The formulation of the interaction of matter with singular light fields needs special care. In a recent article [G. F. Quinteiro, Phys. Rev. A 91, 033808 (2015)PLRAAN1050-294710.1103/PhysRevA.91.033808] we have shown that the Hamiltonian describing the interaction of a twisted-light beam having parallel orbital and spin angular momenta with a small object located close to the phase singularity can be expressed only in terms of the electric field of the beam. Here we complement our study by providing an interaction Hamiltonian for beams having antiparallel orbital and spin angular momenta. Such beams may exhibit unusually strong magnetic effects. We further extend our formulation to radially and azimuthally polarized beams. The advantages of our formulation are that for all beams the Hamiltonian is written solely in terms of the electric and magnetic fields of the beam and as such it is manifestly gauge invariant. Furthermore, it is intuitive by resembling the well-known expressions in the dipole-electric and dipole-magnetic moment approximations.Fil: Quinteiro, Guillermo Federico. Universidad de Buenos Aires. Facultad de Ciencias Exactas. Departamento de Ecología, Genética y Evolución. Buenos Aires; Argentina. Westfalische Wilhelms Universitat; AlemaniaFil: Reiter, D.E.. Westfalische Wilhelms Universitat; AlemaniaFil: Kuhn, T.. Westfalische Wilhelms Universitat; Alemani

Large centroid shifts of vortex beams reflected from multi-layers

Gaussian beams reflected from a multi-layered dielectric experience a shift in their centroid that is different than that from a single interface. This has been previously investigated for linearly polarized beams and, to a much lesser extent, beams with spin angular momentum. Here a combination of theoretical and computational analysis is used to provide a unified quantification of these shifts in layered dielectrics, for light endowed with an intrinsic orbital angular momentum (OAM) - i.e. vortex beams. Two geometries are considered: air/glass/air and glass/air/glass multi-layers. Destructive interference causes singular lateral shifts in the centroid of the reflected vortex beam for which spin alone produces only a mild modulation. In the case of total internal reflection, both spin and intrinsic OAM contribute to an enhancement of these lateral shifts as the interlayer thickness is decreased. This is just the opposite of the trend associated with longitudinal shifts. We find that vortex beams undergo centroid shifts up to tens of microns, more than an order of magnitude larger than for Gaussian beams.Fil: Lusk, Mark T.. Colorado School Of Mines; Estados UnidosFil: Siemens, Mark. University of Denver; Estados UnidosFil: Quinteiro, Guillermo Federico. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Nordeste. Instituto de Modelado e Innovación Tecnológica. Universidad Nacional del Nordeste. Facultad de Ciencias Exactas Naturales y Agrimensura. Instituto de Modelado e Innovación Tecnológica; Argentin

Magnetic-optical transitions induced by twisted light in quantum dots

It has been theoretically predicted that light carrying orbital angular momentum, or twisted light, can be tuned to have a strong magnetic-field component at optical frequencies. We here consider the interaction of these peculiar fields with a semiconductor quantum dot and show that the magnetic interaction results in new types of optical transitions. In particular, a single pulse of such twisted light can drive light-hole-to-conduction band transitions that are cumbersome to produce using conventional Gaussian beams or even twisted light with dominant electric fields.Fil: Quinteiro, Guillermo Federico. Consejo Nacional de Investigaciones Científicas y Técnicas. Universidad de Buenos Aires; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; ArgentinaFil: Reiter, D. E.. Westfalische Wilhelms Universitat; AlemaniaFil: Kuhn, T.. Westfalische Wilhelms Universitat; Alemani