Shear Elastic Modulus of Carbon Fiber Nanotubes

J. Thomas Alford (Northwestern University / Materials Science Major)

Advisor: Prof. John Mintmire
Graduate Student Mentor: Ben Landis

Research Goal: To determine a theoretical shear modulus of elasticity for single walled carbon fiber nanotubes.

Method: Using a python script Professor Mintmire's group is modeling several metallic and non-metallic single walled carbon fiber nanotubes with diameters between .7 nm and 1.8 nm. Because of the way that the python script works we will mostly be working with carbon fiber nanotubes where n1 and n2 are relatively prime for time efficiency, but we will do the calculations for some non relatively prime nanotubes to make sure our results for them is the same as for relatively prime nanotubes. My project is to use the python script to find the net energy (E) as a function of the angular strain and analyze this data to find the torsional elastic constant for multiple single walled nanotubes. The elastic modulus can be defined as the second derivative of energy in respect to the strain. So I graph the energy vs. the strain and determine the second derivative. This data will be compared to various theoretical and experimental values.

Current Progress: Professor Mintmire expected that the resultJanuary 10, 2006parabolic function as predicted from a graphitic system. So far the data the computer has produced on my project has been almost perfectly parabolic as expected. We currently have data on 12 types of single walled carbon nanotubes with data processing for 3 more. I am about to start calculating the energy per carbon and the moduli for the various nanotubes.

Measuring the Force of an Optical Trap Using Lasers of Diverse Wavelengths

Matt Andrews (Oklahoma State University / Electrical and Computer Engineering Major)

Advisor: Prof. James Wicksted
Graduate Student Mentor: Emanuela Ene

One of the most useful tools, at the present, in photonics is the optical trap, also called tweezers. These tweezers allow users to examine micro particles like never before. This is because the particle is being held simply by a laser beam and there are no other chemical or physical "holding systems" in place. Because of this, we are able to measure the force the trap exerts on the particle inside the trap. This will be done by trapping a polystyrene micro-sphere in the tweezer and moving the particle until it escapes the trap. The velocity of the particle at this instance, along with knowledge of the fluid in which the particle is in, will give us the maximum force exerted by the laser on the micro-sphere.

Initially we will be using a low cost setup. This will include the following:

1. Steering mirrors to clarify the Gaussian beam.
2. A beam expander to make the beam hit the objective with maximum intensity.
3. A focusing lens to set the proper radius of curvature for the objective.
4. One pinhole to clean the edges of the beam.
5. An objective to focus the beam to a microscopic waist.

The above system will focus a near perfect Gaussian beam upon a polystyrene micro-sphere with enough power to trap it.

Future Research:
Tweezing is the ultimate way to hold a micro-object for RAMAN spectra. We will use the tweezer to bring micro-spheres with attached silver nano-particles near living cells, in order to enhance the image. Because the cell will not be being held by any physical or chemical means, it will remain undamaged. This will give us new insight into the workings of cellular processes.

Reference:
Gary Boas; p.18, Biophotonics International: April 2004.
Joseph T. Verdeyen; Laser Electronics
Melles Grios catalog 2004

Preliminary Investigations of Quantum Chaos

Jason Cartwright (The University of Texas at Austin / Physics Major)

Advisor: Prof. Gil Summy
Graduate Student Mentors: Peyman Ahmadi and Brian Timmons

Some classical systems can exhibit chaotic behavior and by chaotic we mean that the phase space of a system is not bounded to a finite number of trajectories e.g. on the Poincare map. Or as a restatement, the momentum is not periodic. But the very foundation of quantum mechanics is that particles have bound energy states. Then where does chaos come into play? In one experiment by the Raizen group they pulse a standing electromagnetic radiation (EMR) wave across a BEC gas and then let the gas warm up. In doing so the gas expands, the EMR diffracts off the gas atoms, and they measure the spread in diffraction orders, which can be related to momentum. What they find is that up until a certain time on the order of 10 ns the behavior of the diffracted EMR is "diffusive" (chaotic). After this "quantum break time" the system settles into a state of quasiperiodicity. What we will do in Dr. Summy's group is something similar to Raizen's group but in the space, instead of time, domain. We will be looking at light diffracted in the near field. We will be using hologram diffraction gratings that are created by making a hologram of an interference pattern. We will make a number of these gratings, which will be separated by a distance equal the Talbot length wherein an image reproduces itself. Incident light will pass thru many gratings before finally emerging with an image in the near field where we measure the number of diffraction orders. The light will be a red diode laser, and the hologram gratings will be phase gratings. We hope to use a similar method in the future using a BEC atomic laser incident upon hologram gratings.

Fabrication of Matching Optical Delay Lines with 820nm Single Mode Fiber

Christine G. Co (Oklahoma State University / Electrical and Computer Engineering Major)

Advisor: Prof. Alan Cheville
Graduate Student Mentor: Stacee Harmon

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 milimeters. An Ericsson FSU 925 Fusion Splicer will be used to make a calculated length of stretch. The fiber's new optical path will then be compared to the optical path of a reference single mode fiber. My research this summer will focus on the development of a practical and accurate fiber stretching technique.

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

Elijah Dale (Oklahoma State University / Physics and Aerospace Engineering Major)

Advisor: Prof. Al Rosenberger
Graduate Student Mentor: Michael Humphrey

In support of the research performed by Prof. A. T. Rosenberger and NASA's Dave Smith et. al [1], the topics being investigated are the coupling requirements between two microresonators in a two-resonator system necessary to produce Coupled Resonator Induced Transparency (CRIT) and Coupled Resonator Induced Absorption (CRIA), which are analogous to electromagnetically-induced transparency and electromagnetically-induced absorption in atomic systems, respectively.

Experimentally, a biconically tapered fused-silica fiber is used to couple light into a fused-silica microsphere. In a coupled optical system, the factors that determine observed throughput power are the intrinsic loss ?L and a phase shift between resonator and optical fiber. Three distinct coupling conditions can exist within these systems with each condition being defined by its transmission T and intrinsic losses ?L. In a critically coupled system the light coupled back into the optical fiber is equal in magnitude but opposite in phase to the incident light resulting in no observed throughput for the system. In an overcoupled system, T > ?L, the light coupled back into the optical fiber is greater in magnitude but opposite in phase resulting in an apparent inverting of the throughput field. In an undercoupled system, T < ?L, the light coupled back into the optical fiber is decreased in magnitude but opposite in phase resulting in a decrease of total throughput power.

With the addition of another resonator into the system, coupled to the first resonator, additional effects can be seen due to the phase shift resonator-to-resonator. In both of the following two cases, the primary resonator coupled to the optical fiber is overcoupled initially. The first such case is CRIA in which the destructive interference caused by the resonator-to-resonator coupling can cause the system to appear critically coupled; i.e. at resonance, the system throughput power is zero. The second case is CRIT in which the phase interactions can cause the system to appear strongly undercoupled; i.e. at resonance, the system throughput power is equal to the incident power of the optical fiber.

Specifically, the goals for the research being performed this summer are to calculate the coupling coefficient requirements to produce the CRIT and CRIA states through calculation of spatial field overlap between the resonators using coupled-mode theory. Within these calculations, both fundamental polar and radial modes will be investigated as well as higher-order modes for both polar and radial modes. Furthermore, the sphere sizes, separation distance between primary and secondary resonator and equatorial alignment will be greatly varied to study their effects both directly on coupling and indirectly on the production of the CRIT and CRIA states. These calculations are critical to predict the conditions necessary in the lab for researchers to further investigate and verify the experimental effects in these systems.

[1] D.D. Smith, H. Chang, K.A.Fuller, A.T. Rosenberger and R. Boyd , Phys. Rev. A 69, 063804 (2004).

Photochromic and Photorefractive Evaluation of Transitional Metal Doped LiNbO₃

Rebekah Esmaili (James Madison University / Physics Major)

Advisor: Prof. Joel Martin
Graduate Student Mentor: Walid Hikal

I will be investigating the photoinduced absorption (photochromic) in LiNbO₃ (LN) doped with transitional metal ions. Not all samples are expected to show a photoinduced change in absorption. Bleaching and anneal studies will be made on selected samples with interesting effects.

At the present time I am working on exposing LN samples to ultraviolet (UV) light (400 nm specifically) and looking for absorption differences between unexposed spectra and the UV exposed spectra.

In later weeks I will analyze the photorefractive properties of the crystal using 514 nm light and 633 nm light and also with different grating spacings.

Design, Construction, and Testing of a Laser Scanning System

Josh Munger (Oklahoma State University / Electrical and Computer Engineering Major)

Advisor: Prof. Alan Cheville

Introduction
This project consists of the design, construction, and testing of a laser scanning system that will operate at a higher frequency than the current system allowing for faster acquisition of data. This is accomplished by reflecting a laser beam with two scanners then sending it back along its original path with a roof mirror. The oscillation of the two scanners alters the distance traveled by the laser beam creating the time delay necessary for this process.

Design
Starting from scratch, parts must be ordered first. These include two scanners with their driver, a v-block at exactly ninety degrees, and first surface mirrors to attach to the v-block to make a roof mirror. While the parts ship, I learn to use MatLab and write a simulation program to aid in understanding the system. I also practice aligning optics in the lab.

Construction
The scanners need bases and the v-block needs holes drilled to mount it properly. I can make the scanner bases out of aluminum in the machine shop. Mike Lucas has to do special drilling on the hardened v-blocks. The mirrors must be attached to the v-block with epoxy. With all the parts completed, I begin setting up the system.

Testing
When something does not work as expected, I go back to the design stage and modify the MatLab code trying to find possible causes for the error. This may require reconstructing the system with a different configuration. Once a working configuration is achieved, the system is ready to be tested in a graduate student's experiment. I work with Mo and observe how effectively it works. If more problems are encountered, then analysis and possible redesign are in order until a fully functional system is created.

The results will be presented with a full report at the end of the eight weeks.

Properties of Nonmetal Single-Wall Carbon Nanotubes

Shagoto Nandi (Boston University / Computer Science Major)

Advisor: Prof. John Mintmire
Graduate Student Mentor: Shelly Elizondo

My goal will be to research the properties of nonmetal Single-Wall Carbon Nanotubes(SWNTs). In this I will observe the band structures for some SWNTs whose N1 and N2 values are relatively prime for calculation purposes. From these I can run calculations on the optical cross sections of the SWNT on the OKRA Beowulf Cluster. Also I can plot the fluorescence intensity and excitation and emission wavelengths using SM software on the cluster. After that I can compare the results of plots and data with those given in the research paper Structure-Assigned Optical Spectra of Single-Walled Carbon Nanotubes, written by Sergei M. Bachilo, Michael S. Strano, Carter Kittrell, Robert H. Hauge, Richard E. Smalley, and R. Bruce Weisman. Specifically, I can compare Excitation/Emission wavelengths with those shown in Structure-Assigned Optical Spectra of Single-Walled Carbon Nanotubes figures A, B, C, and D.

Hydrogen Bond Interactions of Amino Acids

David Paige (Oklahoma State University / Physics and Mathematics Major)

Advisor: Prof. Aihua Xie
Graduate Student Mentor: Beining Nie

Research Summary

1. Investigate the hydrogen bond interactions between a protonated carboxylic group and various hydrogen bonding amino acid side chain groups. Perform energy and frequency analysis.
2. Investigate the hydrogen bond interactions between a phenol group (the side chain group of the amino acid Tyrosine) and other amino acid side groups. Again perform energy and frequency analysis.
3. Perform steady state FTIR measurements of a tyrosine model compound (4-ethylphenol).
4. Perform time resolved steady state rapid-scan FTIR measurements of the H108F mutant of the PYP protein at various pH levels and at 295K.

Hypothesized Reaction Pathways for the Degradation of Trinitrotoluene in the Presence of Tetraphenylporphyrinsulfonate (TPPS) and Fe-TPPS

Ryan Scott (Oklahoma State University / Physics and Mathematics Major)

Advisor: Prof. Tim Wilson

Hypothesized reaction pathways for the degradation of trinitrotoluene in the presence of tetraphenylporphyrinsulfonate (TPPS) and Fe-TPPS will be analyzed. Enthalpy calculations for intermediary reaction steps will be calculated using ab initio electronic structure principles using density functional theory.

Monolayer Structures of Tri-Octyl Phosphine Oxide

Eric Tong (Duke University / Physics and Economics Major)

Advisor: Prof. Bret Flanders

This summer we will be continuing the study of the monolayer structures of tri-octyl phosphine oxide through the compression and expansion of the monolayer. We plan using different mixed samples of DPPC and TOPO to study the differences in the isotherms in the different mixture ratios. Additionally we will perform AFM studies on the TOPO monolayer to determine the structure of the monolayer at different surface pressures. Structures to be examined include six fold lattice networks and buckling. Also studied will be the reversibility of the expansion and compression cycles of the monolayer.

Setting Up A Dichroic Atomic Vapor Laser Locking (DAVLL) System

Jonathan White (Oklahoma State University / Physics Major)

Advisor: Prof. Gil Summy
Graduate Student Mentors: Peyman Ahmadi and Brian Timmons

For the REU program, I am going to be setting up a Dichroic Atomic Vapor Laser Locking (DAVLL) system. This is a method used to stabilize a diode laser's frequency to oscillate no more than one megahertz. Laser locking is very important in laser cooling and trapping because the diode laser must be stabilized to the atomic resonance frequency of the atoms. The DAVLL technique has the benefit of being able to tune the frequency several megahertz off a resonance while still maintaining a lock. Once I successfully establish this system it will be integrated into Dr. Summy's Bose-Einstein Condensation experiment.

The DAVLL system consists of a laser diode that is first reflected off of a diffraction grating in the Littrow configuration. A piezo is set behind the grating so that the angle of the grating can be adjusted which changes the frequency of the laser. The beam is then sent through a polarizer in order to make sure the light is linearly polarized. Next the beam passes through an 87Rb vapor cell. A uniform magnetic field is then applied across the vapor cell causing a Zeeman energy split in the atomic transitions. The + polarized light is absorbed by the mf = +1 transitions and the - polarized light is absorbed by the mf = -1 transitions. The light exiting the vapor cell is sent through a quarter-wave plate in order to change the circular polarizations to linear polarizations. A polarizing beam splitter then separates the two polarization states which are sent to two different detectors. The absorption signals can be subtracted from one another to form a DAVLL signal. This signal is sent through a servo-lock circuit which controls the voltage across the piezo. Therefore, when the frequency of the laser starts to drift, the DAVLL signal will change. This causes the servo-lock circuit to adjust the piezo voltage. In this manner, the frequency can be constantly monitored and tweaked as needed.