Brian J. Orr

Bio: Brian J. Orr is an academic researcher from Macquarie University. The author has contributed to research in topics: Optical parametric oscillator & Rotational–vibrational spectroscopy. The author has an hindex of 30, co-authored 191 publications receiving 4546 citations. Previous affiliations of Brian J. Orr include University of Waterloo & University of Sydney.

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.

A Discussion on photoelectron spectroscopy - Angular distributions and intensity in molecular photoelectron spectroscopy I. General theory for diatomic molecules

Abstract: A theory of the angular distribution of photoelectrons ejected with a given energy from diatomic molecules is presented. The differential cross-section OO is of the form a = ^ [l+ /JP ,(co»® )] where O Total is the total cross-section, B an anisotropy parameter and O the angle between the polarization vector of the incident light and the direction of the photoelectron. Expressions for O total and B in terms of internal transition dipole moments are obtained for transitions between individual rotational states of the molecule and ion, for either of Hund’s cases (a) or (b) . The formulae have been developed for central-field bases for the eigenstates of the electron before and after ionization. When rotational structure in the photoelectron spectrum is unresolved the angular distribution is independent of the choice of Hund’s case

Angular distribution and intensity in molecular photoelectron spectroscopy I. General theory for diatomic molecules

Abstract: A theory of the angular distribution of photoelectrons ejected with a given energy from diatomic molecules is presented. The differential cross-section σΩ is of the form σ Ω = σ total 4 π [ 1 + β P 2 ( cos Θ ) ] where σtotal is the total cross-section, β an anisotropy parameter and Θ the angle between the polarization vector of the incident light and the direction of the photoelectron. Expressions for σtotal and β in terms of internal transition dipole moments are obtained for transitions between individual rotational states of the molecule and ion, for either of Hund's cases (a) or (b). The formulae have been developed for central-field bases for the eigenstates of die electron before and after ionization. When rotational structure in the photoelectron spectrum is unresolved the angular distribution is independent of the choice of Hund's case.

Optical heterodyne detection in optical cavity ringdown spectroscopy

Abstract: The present invention relates to optical heterodyne detection cavity ringdown spectroscopy. In one aspect the invention relates to an optical system (1) comprising a ringdown cavity cell (3) defining a resonant optical cavity, means for directing coherent light selected from the group consisting of continuous or quasi-continuous light into said optical cavity (8, 9, 10, 11 and 12), means for altering the resonant optical cavity so as to generate a frequency shift of the coherent light in the optical cavity (6, 7), means for coupling said coherent light into the optical cavity and means for decoupling the frequency shifted coherent light out of said optical cavity (5, 6, 7), means for optically combining (10, 11, 12) said decoupled frequency shifted coherent light with another portion of coherent light not in optical communication with the optical cavity and means for optical heterodyne detection (13) of the intensity of said combined light. A method for optical detection is also described as well as methods and apparatus for detecting a parameter of a sample.

Kerr effect in methane and its four fluorinated derivatives

Abstract: Electric birefringence has been measured at a wavelength of 632.8 nm over a range of temperature and pressure in the gases CH4, CH3F, CH2F2, CHF3 and CF4. The results yield values of the second hyperpolarizability γ for CH4 and CF4 and, for CH3F, CH2F2 and CHF3, the first hyperpolarizability β and the difference (α33–α) between the optical polarizability component in the direction of the molecular dipole and its mean. For CH2F2(α33–α) is unusually small; the birefringence changes sign as the pressure is increased, the change occurring at 1.7 bar at 244°K. Limitations of a bond additivity model for β are exposed, and the importance of hyperpolarizability contributions to the Kerr constant demonstrated. The density dependence of the birefringence in the five gases is compared with the predictions of simple theoretical models, but agreement is in most cases poor.

Gaussian basis sets for use in correlated molecular calculations. IV. Calculation of static electrical response properties

Abstract: An accurate description of the electrical properties of atoms and molecules is critical for quantitative predictions of the nonlinear properties of molecules and of long‐range atomic and molecular interactions between both neutral and charged species. We report a systematic study of the basis sets required to obtain accurate correlated values for the static dipole (α1), quadrupole (α2), and octopole (α3) polarizabilities and the hyperpolarizability (γ) of the rare gas atoms He, Ne, and Ar. Several methods of correlation treatment were examined, including various orders of Moller–Plesset perturbation theory (MP2, MP3, MP4), coupled‐cluster theory with and without perturbative treatment of triple excitations [CCSD, CCSD(T)], and singles and doubles configuration interaction (CISD). All of the basis sets considered here were constructed by adding even‐tempered sets of diffuse functions to the correlation consistent basis sets of Dunning and co‐workers. With multiply‐augmented sets we find that the electrical properties of the rare gas atoms converge smoothly to values that are in excellent agreement with the available experimental data and/or previously computed results. As a further test of the basis sets presented here, the dipole polarizabilities of the F− and Cl− anions and of the HCl and N2 molecules are also reported.

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.

Optical gas sensing: a review

Abstract: The detection and measurement of gas concentrations using the characteristic optical absorption of the gas species is important for both understanding and monitoring a variety of phenomena from industrial processes to environmental change. This study reviews the field, covering several individual gas detection techniques including non-dispersive infrared, spectrophotometry, tunable diode laser spectroscopy and photoacoustic spectroscopy. We present the basis for each technique, recent developments in methods and performance limitations. The technology available to support this field, in terms of key components such as light sources and gas cells, has advanced rapidly in recent years and we discuss these new developments. Finally, we present a performance comparison of different techniques, taking data reported over the preceding decade, and draw conclusions from this benchmarking.

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.