Genetic algorithm for the response of arbitrarily twisted nematic liquid crystals to an applied field.

When an external field is applied across a liquid-crystal cell, the twist and tilt distributions cannot be calculated analytically and must be extracted numerically. In the standard approach, the Euler-Lagrange equations are derived from the minimization of the free energy of the system and then solved via finite-difference methods, often implemented in commercial software. These tools iterate from initial solutions that are compatible with the boundary conditions, providing limited to no flexibility for customization.

Full Spatial Characterization of Entangled Structured Photons.

Vector modes are fully polarized modes of light with spatially varying polarization distributions, and they have found widespread use in numerous applications such as microscopy, metrology, optical trapping, nanophotonics, and communications. The entanglement of such modes has attracted significant interest, and it has been shown to have tremendous potential in expanding existing applications and enabling new ones. However, due to the complex spatially varying polarization structure of entangled vector modes (EVMs), a complete entanglement characterization of these modes remains challenging and time consuming.

Two-photon interference: the Hong-Ou-Mandel effect.

Nearly 30 years ago, two-photon interference was observed, marking the beginning of a new quantum era. Indeed, two-photon interference has no classical analogue, giving it a distinct advantage for a range of applications. The peculiarities of quantum physics may now be used to our advantage to outperform classical computations, securely communicate information, simulate highly complex physical systems and increase the sensitivity of precise measurements.

Characterization of an underwater channel for quantum communications in the Ottawa River.

We examine the propagation of optical beams possessing different polarization states and spatial modes through the Ottawa River in Canada. A Shack-Hartmann wavefront sensor is used to record the distorted beam's wavefront. The turbulence in the underwater channel is analysed, and associated Zernike coefficients are obtained in real-time.

Interaction-free ghost-imaging of structured objects.

Quantum - or classically correlated - light can be employed in various ways to improve resolution and measurement sensitivity. In an "interaction-free" measurement, a single photon can be used to reveal the presence of an object placed within one arm of an interferometer without being absorbed by it. With a technique known as "ghost-imaging", entangled photon pairs are used for detecting an opaque object with significantly improved signal-to-noise ratio while preventing over-illumination.

Quantum cryptography with structured photons through a vortex fiber.

Optical fiber links and networks are integral components within and between cities' communication infrastructures. Implementing quantum cryptographic protocols on either existing or new fiber links will provide information-theoretical security to fiber data transmissions. However, there is a need for ways to increase the channel bandwidth.

Quantum cryptography with twisted photons through an outdoor underwater channel.

Quantum communication has been successfully implemented in optical fibres and through free-space. Fibre systems, though capable of fast key and low error rates, are impractical in communicating with destinations without an established fibre link. Free-space quantum channels can overcome such limitations and reach long distances with the advent of satellite-to-ground links.

Unimolecular reaction energies for polycyclic aromatic hydrocarbon ions.

Imaging photoelectron photoion coincidence spectroscopy was employed to explore the unimolecular dissociation of the ionized polycyclic aromatic hydrocarbons (PAHs) acenaphthylene, fluorene, cyclopenta[d,e,f]phenanthrene, pyrene, perylene, fluoranthene, dibenzo[a,e]pyrene, dibenzo[a,l]pyrene, coronene and corannulene. The primary reaction is always hydrogen atom loss, with the smaller species also exhibiting loss of CH to varying extents. Combined with previous work on smaller PAH ions, trends in the reaction energies (E) for loss of H from sp-C and sp-C centres, along with hydrocarbon molecule loss were found as a function of the number of carbon atoms in the ionized PAHs ranging in size from naphthalene to coronene.

Nondestructive Measurement of Orbital Angular Momentum for an Electron Beam.

Free electrons with a helical phase front, referred to as "twisted" electrons, possess an orbital angular momentum (OAM) and, hence, a quantized magnetic dipole moment along their propagation direction. This intrinsic magnetic moment can be used to probe material properties. Twisted electrons thus have numerous potential applications in materials science.

Dissociative photoionization and threshold photoelectron spectra of polycyclic aromatic hydrocarbon fragments: an imaging photoelectron photoion coincidence (iPEPICO) study of four substituted benzene radical cations.

Four molecules were investigated by imaging photoelectron photoion coincidence (iPEPICO) spectroscopy: 1-propynylbenzene, indene, ethynylbenzene, and benzocyclobutene. Their threshold photoelectron spectrum was obtained and electronic transitions were assigned by OVGF (outer valence Green's function) calculations. Vibrational progressions observed in the electronic ground and excited states were simulated by calculating Franck-Condon factors based on the neutral as well as the cation ground and excited state geometries.

Dissociation of the anthracene radical cation: a comparative look at iPEPICO and collision-induced dissociation mass spectrometry results.

The dissociation of the anthracene radical cation has been studied using two different methods: imaging photoelectron photoion coincidence spectrometry (iPEPCO) and atmospheric pressure chemical ionization-collision induced dissociation mass spectrometry (APCI-CID). Four reactions were investigated: (R1) C14H10(+•) → C14H9(+) + H, (R2) C14H9(+) → C14H8(+•) + H, (R3) C14H10(+•) → C12H8(+•) + C2H2 and (R4) C14H10(+•) → C10H8(+•) + C4H2. An attempt was made to assign structures to each fragment ion, and although there is still room for debate whether for the C12H8(+•) fragment ion is a cyclobuta[b]naphthalene or a biphenylene cation, our modeling results and calculations appear to suggest the more likely structure is cyclobuta[b]naphthalene.