1:30 pm

Ab Initio Study of a Hypothesized Trinitrotoluene Degradation Reaction Pathway

Ryan Scott and Tim Wilson, Department of Physics, Oklahoma State University, Stillwater, OK 74078.

Abstract

The enthalpy of reaction is calculated for each step in a hypothesized reaction pathway involving the degradation of trinitrotoluene. GAUSSIAN 03 electronic structure codes are used to calculate the optimized ground state energy and vibrational, rotational, and translational energies of the products and reactants involved. Density functional method (B3LYP), basis set 6-31G(d,p), and the SCRF method for the implementation of a dielectric screen were used for each calculation. All reactions are also assumed to occur in a water solvent at room temperature.

1:50 pm

Calculation of Coupling Strength Between Whispering Gallery Modes in a Dual Microsphere System

Elijah Dale, Michael J. Humphrey, A. T. Rosenberger, and D. K. Bandy, Department of Physics, Oklahoma State University, Stillwater, Oklahoma 74078.

Abstract

Coupled-mode theory is used to numerically calculate the coupling coefficients between transverse electric modes of various polar and radial order within a dual fused-silica microsphere system. The results of these calculations suggest that the overall coupling coefficients are largely independent of the relative radii of the coupled microspheres. Furthermore, within these calculations it is found that coupling is strongly dependent on spatial field overlap between modes of different polar order while strongly dependent on phase matching between modes of different radial order. The results of these calculations are in good agreement with experimental results.

2:10 pm

Fabrication of Matching Optical Delay Lines with 820nm SingJanuary 10, 2006o, R. A. Cheville, Department of Electrical and Computer Engineering, Oklahoma State University, Stillwater OK, 74078.

Abstract

A terahertz transmitter consisting of an array of photoconductive switches requires precisely matched optical delay lines for the femtosecond laser excitation pulses. The purpose of this study was to develop an accurate and consistent method of stretching 820nm single mode optical fiber to sub-millimeter accuracy. Cutting the fiber to match the length of the reference fiber is not practical because it only yields accuracy within a few millimeters. An Ericsson FSU 925 Fusion Splicer was used to make a calculated length of stretch and the fiber’s new optical path was then be compared to the optical path of a reference single mode fiber. We are continuing modifications for the tapering method in order to develop a precise technique for in situ fiber stretching.

 

2:30 – 2:50 pm Intermission

 

2:50 pm

Optical Delay Using Resonant Optical Scanners

Joshua D. Munger and R. Alan Cheville, Department of Electrical and Computer Engineering, Oklahoma State University, Stillwater OK, 74078.

Abstract

An ongoing problem in ultrafast optical experiment is providing a time varying optical delay. For rapid data acquisition the defining factor is the scan rate given as a velocity (m/s) where a longer change in optical path length (m) in a short time period (s) is desirable. A pair of resonant optical scanners in conjunction with a roof mirror has been used to create a time-varying delay. By having the angular positions of two mirrors vary sinusoidally with equal amplitudes and locked in phase, the delay varies sinusoidally. This method has been used to measure a signal from a terahertz spectroscopy system, and can potentially allow data acquisition to occur more than six times faster.

3:10 pm

Theoretical Elastic Properties of Single Walled Carbon Nanotubes

J. Thomas Alford, Ben Landis, John W. Mintmire, Department of Physics, Oklahoma State University
Stillwater, OK 74078.

Abstract

Carbon fiber nanotubes are a relatively new material with amazing physical and electrical properties. Several of these properties have been predicted theoretically, as well as observed experimentally, and include a Young modulus on the order of 1 TPa and high conductivity in certain nanotubes. In this paper we report the results of the first principle calculations for the physical properties of several single wall carbon nanotubes (SWNT) with radii between 3 and 8 Ǻ. After discussion of our data for both the Young modulus and shear modulus for several SWNTs, we will compare these values to other studies and the values of these properties predicted by a simple graphene tube.

3:30 pm

Optical Properties of Single-Walled Carbon Nanotubes

Shagoto Nandi, S. L. Elizondo, J. W. Mintmire, Department of Physics, Oklahoma State University, Stillwater, OK 74078.

Abstract

Calculations on the electronic properties of single-walled carbon nanotubes (SWNT) can be made using a first principles local-density functional method. From this the optical cross sections can be obtained and the components can be plotted against the excitation energy. This will result in a plot from which the peaks can be used to describe the absorption and emission of specific nanotubes. We can make plots of the excitation wavelength and emission wavelength using the optical cross section peaks. Bachilo, et.al report a spectroflourimetric study in which distinct first and second van Hove optical transitions are measured for 33 different nanotubes and assigned to specific structures [1]. In their data they report the ratio of optical excitation to emission energies plots for each peak versus the peak's excitation wavelength and their results show a linear pattern through the experimental points qualitatively resembling the computed findings using an extended tight-binding model calculation on SWNTs. Using first principles calculations and analyzing the optical data, we compare results with previous work to see whether or not such patterns can be determined.

[1] S.M Bachilo, M.S. Strano, C. Kittrell, R.H. Hauge, R.E. Smalley, R.B Weisman, Science 298, 2361 (2002).

1:30 pm

The Formation of Three Dimensional Bud-Like Structures in Various Tri-Octyl Phosphine Oxide and 1,2-Dipalmitoyl–sn-Glycero-3-Phosphocholine Mixtures

Eric A. Tong* and Bret N. Flanders, Department of Physics, Oklahoma State University, Stillwater, OK 74078.

Abstract

The surface pressure-area isotherms of different tri-octyl phosphine oxide (TOPO) and 1,2-dipalmitoyl–sn-glycero-3-phosphocholine (DPPC) mixture monolayers were collected on the air-water interface. Most of these isotherms exhibited a plateau at a surface pressure between 30mN/m and 40mN/m, similar to the plateau of pure TOPO monolayer isotherms. However, after continual compression, these isotherms also showed a secondary liftoff which do not exist in the pure TOPO case. The lengths of the plateaus on these isotherms are dependent on the mole percent of the mixtures; as the mole percent of TOPO increases, the plateau length also increases. Through AFM microscopy, small bud-like structures were observed on pure TOPO monolayer at surface pressures in its plateau region. These behaviors suggest that both the mixtures of DPPC and TOPO and pure TOPO form these bud-like structures under the two dimensional monolayer in order to undergo compression without increasing the surface pressure of the interface.

*Department of Physics, Duke University, Durham, North Carolina

1:50 pm

Hydrogen Bonding Interactions Between Amino Acid Side Chains and Isotopic Labeling of Tyrosine for Infrared Spectroscopy

David Paige, Beining Nie and Aihua Xie, Department of Physics, Oklahoma State University, Stillwater, Oklahoma 74078.

Abstract

Infrared Spectroscopy is an important technique for studying protein structure and dynamics. Fourier Transform Infrared Spectroscopy (or FTIR) is a form of infrared spectroscopy which has several key advantages. First it has high wavenumber accuracy and allows the creation of very high-resolution instruments. Secondly, the Jacquinot advantage arises from the circular apertures used in FTIR apparatuses, which have larger areas than the corresponding linear apertures in traditional spectrometers. Finally, the use of a Michelson interferometer allows very good time resolutions, essential to any detailed study of protein dynamics.1 Tyrosine (Tyr) and aspartic acid (Asp) are two amino acids which play an important role in many protein structures. Theoretical ab initio calculations of frequency are important in determining the interaction of these two amino acids with other side chains so that protein structure can be better understood. Finally, isotopic labeling of tyrosine can provide important clues for the deduction of protein function.

2:10 pm

Photorefractive Evaluation of LiNbO3 Co-doped with Fe and Ni

Rebekah Esmaili, Joel J. Martin, and Walid Hikal, Department of Physics, Oklahoma State University, Stillwater, OK 74078.

Abstract

The photorefractive properties of LiNbO3 (LN) improve when doped with certain transition metals, in particular iron and nickel. LN doped with Fe and co-doped with Fe and Ni were measured at three different wavelengths in the visible and near-infrared. The three crystals that showed improved optical performance were LN:0.1%Fe, LN:0.05%Fe + 0.1%Ni, and LN:0.2% Fe + 0.1% Ni. The photorefractive response was measured by writing a simple holographic grating with two crossed laser beams; one beam was interrupted periodically to read the Bragg reflected signal of the other beam. At 514 nm LN:0.2% Fe + 0.1% Ni had a slightly faster rise time but the magnitudes of gratings for all three samples were about the same. Diffraction efficiency at 633 nm light improved with increased percentages of iron. However, at 784 nm LN:0.2% Fe + 0.1% Ni showed a significantly improved performance over the other two samples. At 784 nm the excitation is into a broad Ni2+ internal transition. It appears that this excitation may couple to the Fe and free charge necessary for the photorefractive effect.

This research was supported by the National Science Foundation-Research Experience for Undergraduates, the Air Force Research Laboratory, WPAFB, and the Anteon Corporation.

2:30 – 2:50 pm Intermission

2:50 pm

Force Measurement with Optical Tweezers

Matt Andrews, Emanuela Ene, Jerry Morgan, Electrical Engineering and Physics Departments, Oklahoma State University, Stillwater, OK 74078.

Abstract

This experiment is designed to calibrate an optical trap for the purpose of SERS tweezing. In order for this to be done, one must know the forces that are: 1) Being exerted by the tweezers upon the particle, and 2) exerted by the fluid upon the particle. Previously this has been done in order to view biological samples. In this case we are trapping polystyrene spheres in the order of 0.1 to 6.4 microns. Some of the particles have had carbon nano tubes attached to them. The particles are captured because light carries momentum, which is similar to stopping a train with about one trillion ping pong balls. Trapping is accomplished by expanding the laser beam to the size of the objectives first lens and the radius of curvature set to the objective. Force calculations are made by finding the maximum speed one can move the particle while holding the particle in the trap. With this and knowledge of the solution that the particle is submersed in, stokes force can then be calculated.

3:10 pm

Frequency Stabilizing using the DAVLL Technique

Jonathan White, Gil Summy, Ghazal Behin-Aein, and Peyman Ahmadi, Department of Physics, Oklahoma State University, Stillwater, OK 74078.

Abstract

In laser cooling and laser trapping experiments it is very important to have the laser locked to specific frequency without drifting more than 1 MHz. The DAVLL technique, which we have set up, utilizes the dichroic properties of Rb vapor in a magnetic field. The left- and right- circular polarizations are only absorbed by the ml=-1 and the ml=+1 hyperfine transitions respectively. By then separating these polarizations an error signal can be obtained whose locking slope depends on the magnitude of the hyperfine separation (about 500 MHz). We send a 785nm diode laser, reflected off of a diffraction grating, into a Rb vapor cell, which is in a magnetic field of about 100 gauss. The two polarization beams are divided using a quarter wave plate and a polarizing beam splitter, and they are then sent into photodiodes. Through these techniques, we were able to observe the DAVLL signal in the experimental setup.

3:30 pm

Experimental Investigation of Diffraction by Multiple Gratings for use in Quantum Chaos Experiments

Jason Cartwright and G. S. Summy, Department of Physics, Oklahoma State University, Stillwater, Oklahoma 74078.

Abstract

We investigate the spread of momentum in the spatial frequency band due to several diffraction gratings of uniform grating period that are separated by variable distances. The incident plane wave undergoes an evolution by the grating potential, which is affected by the phase modulation depth. The wave then undergoes a second evolution by the different phases from the grating, which depend on grating separation and increase quadratically with increasing diffraction order. Additionally, we note how varying the grating separation effects the positioning of intensity maxima. Finally we discuss the relevance of this work to the study of quantum chaos.