Abstract:
We consider the excitation of Rydberg states through photons carrying an intrinsic orbital angular momentum degree of freedom. Laguerre-Gauss modes, with a helical wave-front structure, correspond to such a set of laser beams, which carry some units of orbital angular momentum in their propagation direction. We demonstrate that, in a proper geometrical setting, this orbital angular momentum can be transferred to the internal degrees of freedom of the atoms, thus violating the standard dipolar selection rules. Higher orbital angular momentum states become accessible through a single photon excitation process. We investigate how the spacial structure of the Laguerre-Gauss beam affects the radial coupling strength, assuming the simplest case of hydrogen-like wavefunctions. Finally we discuss a generalization of the angular momentum coupling, in order to include the effects of the fine and hyperfine splitting, in the context of the Wigner-Eckart theorem.

Abstract:
It is shown that the vector-vortex Laguerre-Gauss modes with polarization-orbital angular momentum (OAM) entanglement are the vector solutions of the Maxwell equations in a graded-index medium. Focusing of linearly and circularly polarized vortex light beams with nonzero azimuthal and radial indices in a cylindrical graded-index medium is investigated. The wave shape variation with distance taking into account the spin-orbit and nonparaxial effects is analyzed. Effect of long-term periodical revival of wave packets due to mode interference in a graded-index cylindrical optical waveguide is demonstrated. High efficiency transfer of a strongly focused spot through an optical waveguide over large distances takes place with a period of revival.

Abstract:
Discrete-Gauss states are a new class of gaussian solutions of the free Schr\"odinger equation owning discrete rotational symmetry. They are obtained by acting with a discrete deformation operator onto Laguerre-Gauss modes. We present a general analytical construction of these states and show the necessary and sufficient condition for them to host embedded dark beams structures. We unveil the intimate connection between discrete rotational symmetry, orbital angular momentum, and the generation of focussing dark beams. The distinguishing features of focussing dark beams are discussed. The potential applications of Discrete-Gauss states in advanced optical trapping and quantum information processing are also briefly discussed.

Abstract:
We have investigated the generation of highly pure higher-order Laguerre-Gauss (LG) beams at high laser power of order 100W, the same regime that will be used by 2nd generation gravitational wave interferometers such as Advanced LIGO. We report on the generation of a helical type LG33 mode with a purity of order 97% at a power of 83W, the highest power ever reported in literature for a higher-order LG mode.

Abstract:
This paper theoretically treats the spontaneous resonant inelastic scattering of Laguerre-Gauss (LG) beams from the totally symmetric vibrations of complex polyatomic molecules within the semi-classical framework. We develop an interaction Hamiltonian that accounts for the position of the molecule within the excitation beam to derive the effective differential scattering cross-section of a classical LG beam from a molecule using the frequency domain third order nonlinear optical response function. To gain physical insight into this scattering process, we utilize a model vibronic molecule to study the changes to this scattering process. For specific molecular parameters including vibrational frequency and relative displacement of the involved electronic states, this investigation shows that an incident LG beam asymmetrically enhances one of two participating excitation transitions causing modulation of the interference present in the scattering process. This modulation allows a pathway to coherent control of resonant inelastic scattering from complex, poly-atomic molecules. We discuss the possible application of this control to the resonant x-ray inelastic scattering (RIXS) of small poly-atomic molecules central to applications ranging from single molecule electronics to solar energy science.

Abstract:
We study the establishment of vortex entanglement in remote and weakly interacting Bose Einstein condensates. We consider a two-mode photonic resource entangled in its orbital angular momentum (OAM) degree of freedom and, by exploiting the process of light-to-BEC OAM transfer, demonstrate that such entanglement can be efficiently passed to the matter-like systems. Our proposal thus represents a building block for novel low-dissipation and long-memory communication channels based on OAM. We discuss issues of practical realizability, stressing the feasibility of our scheme and present an operative technique for the indirect inference of the set vortex entanglement.

Abstract:
Scattering of the focused Laguerre-Gaussian beams by a spherical particle is performed. According to the generalized Mie theory, the scattering coefficient expressions are gained. From the numerical simulations of the electric field distribution and scattering intensity of the focused Laguerre-Gaussian beams, the scattering intensities are discussed for different scattering angles, radii of spherical particles and topology changes, and the oscillatory behavior of the scattered intensity distribution is explained by the scattering coefficients. The results show that in the focused Laguerre-Gaussian beams, the backscattering intensity increases with the particle radius; and the particle radius when the scattering intensity begins to increase is related to the topological charge. Comparing with the Gaussian beams, we can see that the focuced Laguerre-Gaussian beams have different the scattering characteristics, so they have potential value for particle size measurement, optical communication, atmospheric backscattering detection, etc.

Abstract:
Based on the method of stationary phase and the theorem of the vectorial structure, the analytical expressions for the vectrorial terms, namely the TE and TM terms, of a linearly polarized Laguerre-Gauss beam are derived in the far-field. According to the far-field energy flux distributions of the TE and TM terms, the ratios of the powers of the TE and TM terms to the power of the Laguerre-Gauss beam are given. The analytical formulae of the far-field divergence angles of the Laguerre-Gauss beam and its TE and TM terms are presented, respectively. A relation among the far-field divergence angles of the TE term, the TM term, and the Laguerre-Gauss beam is also derived. The formulae obtained are applicable not only to the paraxial case, but also to the non-paraxial case. The dependences of the ratios of the powers of the TE and TM terms to the whole power on f-parameter and mode number are numerically examined. The effects of the f-parameter, the mode number, and the linearly polarized angle on the far-field divergence angle of the Laguerre-Gauss beam and its TE and TM terms are also analyzed. This research reveals the far-field divergent properties of the linearly polarized Laguerre-Gauss beam from the vectorial structure, and enriches the recognition of the propagation characteristics of the linearly polarized Laguerre-Gauss beam.

Abstract:
Light beams can carry a discrete, in principle unbounded amount of angular momentum. Examples of such beams, the Laguerre-Gauss modes, are frequently expressed as solutions of the paraxial wave equation. There, they are eigenstates of the orbital angular momentum (OAM) operator. The paraxial solutions predict that beams with large OAM could be used to resolve arbitrarily small distances - a dubious situation. Here we show how to solve that situation by calculating the properties of beams free from the paraxial approximation. We find the surprising result that indeed one can resolve smaller distances with larger OAM, although with decreased visibility. If the visibility is kept constant (for instance at the Rayleigh criterion, the limit where two points are reasonably distinguishable), larger OAM does not provide an advantage. The drop in visibility is due to a field in the direction of propagation, which is neglected within the paraxial limit.