J. F. Ward

Bio: J. F. Ward is an academic researcher from University of Michigan. The author has contributed to research in topics: High harmonic generation & Dispersion (optics). The author has an hindex of 5, co-authored 6 publications receiving 1356 citations.

Perturbation theory of the non-linear optical polarization of an isolated system

Abstract: The non-linear optical polarization of an isolated atom or molecule is treated, giving careful consideration to secular and resonant terms in the perturbation expansion. The Method of Averages introduced by Bogoliubov and Mitropolsky is used. The case where resonance-induced excited state populations are negligible, which is relevant to a wide range of non-linear optical experiments, is examined in detail for polarizations through third order in the perturbing fields. This yields concise expressions which are valid for any combination of applied field frequencies, including static fields.

Measurements of molecular hyperpolarizabilities for ethylene, butadiene, hexatriene, and benzene

Abstract: Third‐order polarizabilities are measured in the gas phase using dc electric‐field induced optical second‐ harmonic generation and are found to be positive in each case.

Vibrational mode contributions to molecular third order polarizabilities

Abstract: Third order polarizabilities for fluorinated methanes and sulphur hexafluoride, derived from three non-linear optical processes are compared. Significant differences beyond those estimated for dispersion are ascribed to vibrational effects. Estimates of the vibrational mode contributions using spectroscopic data, while crude, are consistent with the experimental values. It is concluded that vibrational contributions to third order polarizabilities are significant in specific cases.

Optical third-harmonic generation in the fluorinated methanes and sulfur hexafluoride

Abstract: Optical third‐harmonic generation experiments are used to determine nonlinear polarizabilities for the fluorinated methanes and sulfur hexafluoride. An ambiguity present in previous measurements of third‐harmonic generation in gases is resolved.

Design of Organic Molecules with Large Two-Photon Absorption Cross Sections

Abstract: A strategy for the design of molecules with large two-photon absorption cross sections, δ, was developed, on the basis of the concept that symmetric charge transfer, from the ends of a conjugated system to the middle, or vice versa, upon excitation is correlated to enhanced values of δ. Synthesized bis(styryl)benzene derivatives with donor-π-donor, donor-acceptor-donor, and acceptor-donor-acceptor structural motifs exhibit exceptionally large values of δ, up to about 400 times that of trans-stilbene. Quantum chemical calculations performed on these molecules indicate that substantial symmetric charge redistribution occurs upon excitation and provide δ values in good agreement with experimental values. The combination of large δ and high fluorescence quantum yield or triplet yield exhibited by molecules developed here offers potential for unprecedented brightness in two-photon fluorescent imaging or enhanced photosensitivity in two-photon sensitization, respectively.

Quantum-mechanical condensed matter simulations with CRYSTAL

Abstract: The latest release of the Crystal program for solid-state quantum-mechanical ab initio simulations is presented. The program adopts atom-centered Gaussian-type functions as a basis set, which makes it possible to perform all-electron as well as pseudopotential calculations. Systems of any periodicity can be treated at the same level of accuracy (from 0D molecules, clusters and nanocrystals, to 1D polymers, helices, nanorods, and nanotubes, to 2D monolayers and slab models for surfaces, to actual 3D bulk crystals), without any artificial repetition along nonperiodic directions for 0–2D systems. Density functional theory calculations can be performed with a variety of functionals belonging to several classes: local-density (LDA), generalized-gradient (GGA), meta-GGA, global hybrid, range-separated hybrid, and self-consistent system-specific hybrid. In particular, hybrid functionals can be used at a modest computational cost, comparable to that of pure LDA and GGA formulations, because of the efficient implementation of exact nonlocal Fock exchange. Both translational and point-symmetry features are fully exploited at all steps of the calculation, thus drastically reducing the corresponding computational cost. The various properties computed encompass electronic structure (including magnetic spin-polarized open-shell systems, electron density analysis), geometry (including full or constrained optimization, transition-state search), vibrational properties (frequencies, infrared and Raman intensities, phonon density of states), thermal properties (quasi-harmonic approximation), linear and nonlinear optical properties (static and dynamic [hyper]polarizabilities), strain properties (elasticity, piezoelectricity, photoelasticity), electron transport properties (Boltzmann, transport across nanojunctions), as well as X-ray and inelastic neutron spectra. The program is distributed in serial, parallel, and massively parallel versions. In this paper, the original developments that have been devised and implemented in the last 4 years (since the distribution of the previous public version, Crystal14, occurred in December 2013) are described.