Orbital Angular Momentum Properties Research Articles

Entanglement of photons with complex spatial structure in Hermite-Laguerre-Gaussian modes

Photons with complicated spatial mode structures can be applied for different quantum information tasks. Here, we show the entanglement of photons with complex singularity patterns called Hermite-Laguerre-Gaussian (HLG) modes. Measuring one photon of the entangled pairs by HLG mode basis to define its singularity pattern, we can steer the singularity structure of its partner, while the initial singularity structure of the photons is undefined. We also calculate the HLG specific quantum-correlation function. It can be used to extend the quantum key distribution protocols and to tune experiments dealing with high-order transverse modes. In addition we discuss orbital angular momentum properties of the HLG modes and summarize some features of the singularity pattern of the HLG modes with varying angle parameter.

Optical vortex beam based optical fan for high-precision optical measurements and optical switching.

The polarization and orbital angular momentum properties of light are of great importance in optical science and technology in the fields of high-precision optical measurements and high-capacity and high-speed optical communications. Here we show a method for the construction of a simple and robust scheme to rotate a light beam such as a fan, which is based on a combination of these two properties and using the thermal-dispersion and electro-optical effect of birefringent crystals. Using a computer-based digital image-processing technique, we determine the temperature and thermal-dispersion difference of the crystal with high resolution. We also use the rotation phenomenon to realize thermo-optic and electro-optic switches. The basic operating principles for measurement and switching processes are presented in detail. The methods developed here will have wide practical applicability in various fields, including remote sensing, materials science, and optical communication networks.

Protecting orbital-angular-momentum photons from decoherence in a turbulent atmosphere

One of the most important properties of orbital angular momentum (OAM) of photons is that the Hilbert space required to describe a general quantum state is infinite dimensional. In principle, this could allow for encoding arbitrarily large amounts of quantum information per photon, but in practice, this potential is limited by decoherence and errors. To determine whether photons with OAM are suitable for quantum communication, we numerically simulated their passage through a turbulent atmosphere and the resulting errors. We also proposed an encoding scheme to protect the photons from these errors, and characterized its effectiveness by the channel fidelity.

Local spacetime curvature effects on quantum orbital angular momentum

This paper claims that local spacetime curvature can nontrivially contribute to the properties of orbital angular momentum in quantum mechanics. Of key importance is the demonstration that an extended orbital angular momentum operator due to gravitation can identify the existence of orbital states with half-integer projection quantum numbers m along the axis of quantization, while still preserving integer-valued orbital quantum numbers l for a simply connected topology. The consequences of this possibility are explored in depth, noting that the half-integer m states vanish as required when the locally curved spacetime reduces to a flat spacetime, fully recovering all established properties of orbital angular momentum in this limit. In particular, it is shown that a minimum orbital number of l = 2 is necessary for the gravitational interaction to appear within this context, in perfect correspondence with the spin-2 nature of linearized general relativity.

Focusing of elliptically polarized Gaussian beams through an annular high numerical aperture

Based on the vectorial Debye theory, the focusing properties of the Gaussian beam through an annular high numerical aperture are studied numerically, including the intensity, the phase and the orbital angular momentum properties. Then the influence of certain parameters on the focusing properties is also investigated. It is shown that sub-wavelength elliptical light spots can be obtained. And there exists a vortex in the longitudinal component of the focused field even though the incident beam is Gaussian beam, indicating that the spin angular momentum of the elliptically polarized Gaussian beam is converted into the orbital angular momentum by the focusing.

Temporary negative-ion effects on photon emission from free zinc atoms excited by electron impact

Temporary negative-ion formation has been investigated by observing photon emission from electronimpact-excited 4s4p P1, 4s4p P1, 4s4d D1,2,3, 4s4d D2, and 4s5d D1,2,3 states of zinc. Photon excitation functions are presented for incident electron energies from the first excited state threshold 4.003 eV to the first ionization potential 9.394 eV . The energies of isolated negative-ion resonance structures have been determined by fitting Fano profiles. These energies, and those of key features in the complicated overlapping resonance profiles, are compared with theory and previous experiments. The strength of resonance contributions, and which structures are dominant, depends on the spin and orbital angular momentum properties of the observed state.

Radiation forces on a two-level atom in a σ+ − σ− configuration of Laguerre-Gaussian beams

We investigate the radiation forces associated with the J = 0 → J = 1 transition of a two-level atom in a laser configuration of two counter-propagating Laguerre-Gaussian (LG) beams with opposite circular polarisations. It is shown that, in addition to the usual dissipative and dipole forces, the atom experiences a torque about the beam axis. The latter arises from the orbital angular momentum properties of the Laguerre-Gaussian beams. The atom experiences either a static torque or a purely velocity-dependent torque, depending on the relative signs of the orbital angular momenta of the two LG beams. The trajectories of the atom are calculated in each case by solving the optical Bloch equations together with the classical equation of motion for the atom.

Angular distribution of photoelectrons from fixed-in-space molecules

Angular distributions of 1sσ photoelectrons from spatially fixed N 2 molecules have been measured around the σ ∗ shape resonance in the K-shell continuum. This has been realized with the use of a coincidence technique: by detecting the photoelectron in coincidence with the fragment ion having the information on the molecular orientation at a moment of photoabsorption. The angular distributions obtained by this technique are rich in structure, which are completely different from usual photoelectron angular distributions from randomly oriented molecules. The orbital angular momentum properties of the 1sσ photoelectrons at the σ ∗ shape resonance have been revealed.

Angular distributions of 1s sigma photoelectrons from fixed-in-spaceN2 molecules.

The angular distributions of $1s\ensuremath{\sigma}$ photoelectrons from ${\mathrm{N}}_{2}$ molecules held fixed in space have been measured around the ${\ensuremath{\sigma}}^{*}$ shape resonance for the first time. The angular distributions have been very rich in structure, which are completely different from usual photoelectron angular distributions from randomly oriented molecules, as predicted by Dill. The orbital angular momentum properties of the $1s\ensuremath{\sigma}$ photoelectrons around the ${\ensuremath{\sigma}}^{*}$ shape resonance have been made clear from the angular distribution patterns.