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Articles 1 - 12 of 12
Full-Text Articles in Physical Sciences and Mathematics
Internal Caustic Structure Of Illuminated Liquid Droplets, James A. Lock, Edward A. Hovenac
Internal Caustic Structure Of Illuminated Liquid Droplets, James A. Lock, Edward A. Hovenac
Physics Faculty Publications
The internal electric field of an illuminated liquid droplet is studied in detail with the use of both wave theory and ray theory. The internal field attains its maximum values on the caustics within the droplet. Ray theory is used to determine the equations of these caustics and the density of rays on them. The Debye-series expansion of the interior-field Mie amplitudes is used to calculate the wave-theory version of these caustics. The physical interpretation of the sources of stimulated Raman scattering and fluorescence emission within a liquid droplet is then given.
On Compensation And Conductivity Models For Molecular-Beam-Epitaxial Gaas Grown At Low-Temperature, David C. Look
On Compensation And Conductivity Models For Molecular-Beam-Epitaxial Gaas Grown At Low-Temperature, David C. Look
Physics Faculty Publications
Molecular‐beam‐epitaxial GaAs grown at 200 °C has an extremely high (≳1019 cm−3) concentration of AsGa defects and, after an anneal at 550–600 °C, a high concentration of As precipitates. The relative roles of the AsGa defects and As precipitates in compensation and conductivity is controversial. Here criteria are developed to distinguish between two existing models.
Mie Theory Model Of The Corona, James A. Lock, Leiming Yang
Mie Theory Model Of The Corona, James A. Lock, Leiming Yang
Physics Faculty Publications
We performed a calculation of the corona colors that employed Mie theory to obtain the scattered light intensity. The scattered intensity was integrated over the visible spectrum for a number of different cloud droplet size distributions. The results were converted to chromaticity coordinates, convolved with the angular size of the sun, and plotted on the 1931 CIE chromaticity diagram. The results were compared to observations of multiple-ring coronas. It was found that, when using Mie theory to estimate cloud droplet sizes, water droplets with diameters in the 7-mu-m less-than-or-similar-to D less-than-or-similar-to 15-mu-m range produced the 13 multiple-ring coronas that were …
Light And Color In The Open Air: Introduction By The Feature Editor, James A. Lock, Craig F. Bohren
Light And Color In The Open Air: Introduction By The Feature Editor, James A. Lock, Craig F. Bohren
Physics Faculty Publications
No abstract provided.
Infrared Quenching And Thermal Recovery Of Thermally Stimulated Current Spectra In Gaas, Z-Q. Fang, David C. Look
Infrared Quenching And Thermal Recovery Of Thermally Stimulated Current Spectra In Gaas, Z-Q. Fang, David C. Look
Physics Faculty Publications
Thermally stimulated current (TSC) spectra stimulated by infrared (hν≤1.12 eV) light at 90 K have been used to study the photoquenching and thermal recovery of several dominant TSC peaks in Ga‐rich, semi‐insulating GaAs. The filling‐pulse‐length dependence of the quenching for these traps, and the temperature dependence of their recovery are clearly identified with the ground‐to‐metastable state transition of EL2. The data are consistent with the traps having a direct association with EL2 or EL2∗ rather than an indirect association which could result from a change in the dominant‐free carriers as EL2 transforms to EL2∗. If so, they likely …
Interference Between Diffraction And Transmission In The Mie Extinction Efficiency, James A. Lock, Leiming Yang
Interference Between Diffraction And Transmission In The Mie Extinction Efficiency, James A. Lock, Leiming Yang
Physics Faculty Publications
We give simple analytic and numerical demonstrations showing that the interference structure in the Mie extinction efficiency of a sphere is caused by the interference of the light waves that are diffracted and transmitted in the near-forward direction.
Comparison Of Deep Centers In Semiinsulating Liquid-Encapsulated Czochralski And Vertical-Gradient Freeze Gaas, Z-Q. Fang, David C. Look
Comparison Of Deep Centers In Semiinsulating Liquid-Encapsulated Czochralski And Vertical-Gradient Freeze Gaas, Z-Q. Fang, David C. Look
Physics Faculty Publications
Three‐inch, semi‐insulating (SI) GaAs, grown by the vertical gradient freeze (VGF) technique, has been studied by IR absorption, temperature‐dependent dark current and Hall‐effect, thermally stimulated current (TSC), and photoinduced current transient spectroscopy and has been compared with undoped, SI GaAs, both As‐rich and Ga‐rich, grown by the high‐pressure liquid‐encapsulated Czochralski method. The results clearly indicate that (1) the VGF GaAs contains less EL2, which suggests a less As‐rich crystal stoichiometry; (2) in some VGF samples activation energies of 0.43 or 0.46 eV are deduced from temperature‐dependent carrier concentration or resistivity measurements, respectively, and (3) VGF samples often show a thermal …
On-Wafer Hall-Effect Measurement System, P. D. Mumford, David C. Look
On-Wafer Hall-Effect Measurement System, P. D. Mumford, David C. Look
Physics Faculty Publications
A novel system capable of making on‐wafer Hall‐effect measurements of a patterned wafer during the fabrication sequence has been developed. A flat, powerful rare‐earth magnet provides the magnetic field required. The wafer need only have van der Pauw patterns available for on‐wafer measurement capability. Measurement of room temperature Hall mobility can quickly and easily be obtained, making possible detailed study of carrier concentration and mobility variations during wafer fabrication.
Third‐Order, Nonlinear Optical Interactions Of Some Benzporphyrins, D.V.G.L.N. Rao, Francisco J. Aranda, Joseph F. Roach, David E. Remy
Third‐Order, Nonlinear Optical Interactions Of Some Benzporphyrins, D.V.G.L.N. Rao, Francisco J. Aranda, Joseph F. Roach, David E. Remy
Physics Faculty Publications
We measured third‐order, nonlinear optical susceptibility χ(3) for a series of tetrabenzporphyrins in solution in tetrahydrofuran at 532 nm using degenerate four‐wave mixing with picosecond pulses and obtained values of molecular second hyperpolarizability 〈γ〉. The corresponding macroscopic χ(3) values calculated for nine compounds with different substituent groups are four to five orders larger than CS2. For five of the compounds the χ(3) values are in the range 1.2–2.8×10−8 esu. Our experiments indicate that the nonlinearity is predominately electronic in origin with a response time faster than the 15 ps resolution of our system.
The Jovian Ionospheric E Region, Y. H. Kim, Jane L. Fox
The Jovian Ionospheric E Region, Y. H. Kim, Jane L. Fox
Physics Faculty Publications
We have constructed a model of the Jovian ionosphere that includes direct photoionization of hydrocarbon molecules. A high resolution solar spectrum was synthesized from Hinteregger's solar maximum spectrum (F79050N) and high resolution cross sections for photoabsorption by H2 bands in the range 842 to 1116 Å were constructed. Two strong solar lines and about 30% of the continuum flux between 912 and 1116 Å penetrate below the methane homopause despite strong absorption by CH4 and H2. We find that hydrocarbons (mainly C2H2) are ionized at a maximum rate of 55 cm−3 …
Diffuse Band Profiles In The Spectrum Of Hd 29647: Evidence For A Molecular Origin?, Theodore P. Snow, C G. Seab
Diffuse Band Profiles In The Spectrum Of Hd 29647: Evidence For A Molecular Origin?, Theodore P. Snow, C G. Seab
Physics Faculty Publications
High signal-to-noise ratio spectra have been obtained of the diffuse interstellar bands at 5780 and 5797 Å in the spectrum of HD 29647, a heavily reddened star within or behind a portion of the Taurus dark cloud complex. The observations were made using the coudé spectrograph on the Canada-France-Hawaii Telescope. The Reticon detector combined with the coudé spectrograph and excellent observing conditions allowed S/N ratios as high as 200 for this star, which was V=8.37 and E(B–V)=1.03. In two separate exposures both bands were found to be narrower and weaker than normal values for …
The Venus Ultraviolet Aurora: A Soft Electron Source, Jane L. Fox, A. I. F. Stewart
The Venus Ultraviolet Aurora: A Soft Electron Source, Jane L. Fox, A. I. F. Stewart
Physics Faculty Publications
The Pioneer Venus Orbiter Ultraviolet Spectrometer has recorded continuous but variable emissions of atomic oxygen at 1304 and 1356 Å in images of the nightside of Venus. We show that the observed intensities are consistent with the presence of precipitation of soft electrons into the nightside thermosphere. Model calculations are presented in which upper and lower limits to the magnitude of the electron flux necessary to produce the observed intensities are derived. Constraints are imposed on the energy spectrum of the electrons by the measured ion densities and by the predicted intensities of other emissions that have not been detected.