Bulletin of the American Physical Society
2006 Texas Section of the APS Joint Fall Meeting
Thursday–Saturday, October 5–7, 2006; Arlington, Texas
Session OP1: Optics and Semiconductors |
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Chair: William Graham, Texas Christian University Room: UT Arlington, University Center San Saba |
Friday, October 6, 2006 1:30PM - 1:42PM |
OP1.00001: Three-dimensional photonic crystals formed through a single diffractive optical element Yuankun Lin, David Rivera Photonic crystals are microstructured materials in which the dielectric constant is periodically modulated on a length scale comparable to the desired electromagnetic wavelength of operation. They hold the promise of numerous applications in integrated optical circuits such as enhancing the performance of semiconductor lasers, waveguides, and all on chip optical transistor. We simulate the photonic band structure in woodpile-type photonic crystals and show the fabrication feasibility of these crystals with phase mask based holographic lithography. The experimental demonstration on SU-8 photoresist indicates that a single optical element can replace a complex optical setup for the holographic fabrication of woodpile-type photonic crystals. Photonic band gap calculation predicts the existence of full band gap in these crystals. [Preview Abstract] |
Friday, October 6, 2006 1:42PM - 1:54PM |
OP1.00002: Reverse-Mode Transmission Gratings Holographically Recorded Utilizing Liquid Crystalline Photopolymers Robert Ramsey, Suresh Sharma Reverse-mode transmission gratings are holographically recorded in a polymer dispersed liquid crystal materials set utilizing the 540nm lasing wavelength. The samples are synthesized utilizing mixtures of a reactive mesogen, RM257, nematic liquid crystals E44 and E3100-100, acrylate monomers and a photo- oxidant dye. We investigate the formation parameters, electro- optical and frequency characteristics of these gratings. It is found that for an applied field strength of around 14 V/$\mu$m a relative increase in the diffraction efficiency of almost 1200\% is obtained with switching times of 12ms. [Preview Abstract] |
Friday, October 6, 2006 1:54PM - 2:06PM |
OP1.00003: Spectroscopic analysis of Pr$^{3+}$ (4f$^{2})$ absorption intensities in a plastic host (HEMA). David Stonestreet, Kelly Nash, Doug Dee, Raylon Yow, John Gruber, Dhiraj Sardar A spectroscopic investigation has been performed on the Pr$^{3+}$ ions embedded in 2-hydroxyethyl methacrylate (HEMA) solid plastic host. The standard Judd-Ofelt analysis was applied to the room temperature absorption intensities of Pr$^{3+}$ transitions to determine three phenomenological intensity parameters: $\Omega _{2}$, $\Omega _{4}$ and $\Omega _{6}$. Values of the intensity parameters were subsequently used to determine the decay rates (emission probabilities), radiative lifetimes, and branching ratios of the principal intermanifold transitions of Pr$^{3+}$ from the $^{3}$P$_{2}$, $^{1}$D$_{2}$, and $^{3}$P$_{0}$ manifold states to the lower-lying manifolds. The spectroscopic properties Pr$^{3+}$ in HEMA will be compared with those in glasses. [Preview Abstract] |
Friday, October 6, 2006 2:06PM - 2:18PM |
OP1.00004: Adaptive quantum control of two photon fluorescence on Coumarin 30 by using evolutionary algorithm Milan Poudel, Alexender Kolomenski, Hans Schuessler Two-photon excitation fluorescence of complex molecules (Coumarin-30) is successfully optimized by using feedback control pulse shaping technique. For such an optimization we have implemented an evolutionary algorithm [1], [2] in a Lab-view programming environment with a liquid crystal pulse shaper in a folded 4f set up. In the algorithm, one generation uses 48 individuals (vectors of voltage on the LC matrix).For each generation the fitness value is measured for every setting of the mask. A new generation is built from the previous by combining parents (the fittest individuals) and producing the desired degree of mutations (changes of the vector elements by some random value) to provide reasonable convergence. By successive repetition of this scheme, individuals corresponding to the highest fitness values will survive and produce offspring's for subsequent generations. Typically, convergence to the optimum value was achieved after 30 generations. Without any prior knowledge of the molecular system, the optimization goal was automatically achieved by changing the spectral phases [3]. The pulses before and after optimization were measured with GRENOUILLE, a type of second harmonic frequency resolved optical gating (SH FROG). To find the efficient pulse with lower intensity, three types of optimization were performed, the two photon fluorescence signal, the second harmonic signal and the ratio between them. The Intensity of two photon fluorescence of coumarin-30 could be increased noticeably compared to the transform limited pulse optimizing the second harmonic generation. The experimental results appear to be the potential applications of coherent control to the complicated molecular system as well as in bio medical imaging. [Preview Abstract] |
Friday, October 6, 2006 2:18PM - 2:30PM |
OP1.00005: X-ray diffraction methods for semiconductors structure analysis of photovoltaic devices Fatima Amir, Eduardo Maldonaldo, Kevin Clark, Wiley Kirk X-ray diffraction is a powerful tool for characterizing any kind of crystal; analysis can be performed across a whole spectrum of material types from perfect single crystals to amorphous materials. X-ray methods are generally non-destructive, in that specimen preparation is not required, and they can provide an appropriate route for obtaining structural information on thin films and multilayers without disturbing the layers. To improve the quality of photovoltaic device, it is important to improve the structure of the sample, and have a single crystal. We will report performance of different x-ray experiments on several semiconductor samples involving the molecular beam epitaxy growth of II-VI compound semiconductors on silicon substrates. We will present out of plane, in plane, and reflectivity data that have been taken on various types of samples. [Preview Abstract] |
Friday, October 6, 2006 2:30PM - 2:42PM |
OP1.00006: A novel technique for cleaning semiconductor wafers using ultrasonic transducer Rugved Nakade, Raylon Yow, Tony Sayka, Dhiraj Sardar An experiment was designed based on U.S. Patent no. 6,766,813 which describes a process that effectively cleans a semiconductor wafer with the help of ultrasonic vibrations. The semiconductor wafer was freely supported by a hollow cylindrical box made of foam. Two commonly occurring contaminants found on wafers in the industry are silicon and silicon dioxide. Micrometer sizes of these two materials were used to replicate contaminants that commonly occur in the industry. The wafer was then excited with the help of an ultrasonic transducer in the aim of knocking off these contaminants from the surface of the semiconductor wafer. Particle counts were taken with the help of a modified optical microscope before and after applying the ultrasonic vibration in order to determine the effectiveness of this technique. [Preview Abstract] |
Friday, October 6, 2006 2:42PM - 2:54PM |
OP1.00007: Galvanomagnetic Channel Mobility Measurements of low-k and high-k Transistors. R. Agrawal, R. Mahajan, R.T. Bate, W.P. Kirk, G. Pant, B.E. Gnade, R.M. Wallace This paper reports a different diagnostic technique for SiO$_{2}$ and HfSiO gate stacks which can determine true mobility ($\mu )$ regardless of trap characteristics. It can be used in the wafer fab to give workers greater insight into determining the true drift mobility. Effective mobility ($\mu_{eff})$ measurements in high-k transistors are ambiguous as a diagnostic technique because there are two different mechanisms by which $\mu_{eff}$ can be degraded: (1) Enhanced scattering of carriers by phonons and by charged defects at or near the interface, and (2) Reduction of the channel carrier density by trapping. Conventional measurements cannot distinguish between the two mechanisms of mobility degradation, hence their contributions cannot be determined. The trapping can cause $\mu_{eff}$ to underestimate $\mu$. The potential use of new materials for the conducting channel compounds the uncertainty about what the true $\mu$ should be. So, it is highly desirable to measure both $\mu$ and $\mu_{eff}$ to understand what is limiting the channel current. Our method employs galvanomagnetic (Hall effect \textit{and} magnetoresistance) measurements on SiO$_{2}$ and HfSiO transistors to determine the drift velocity of carriers in the channel, even in the presence of carrier trapping. We will report on Hall and magnetoresistance measurements using specially designed and fabricated low-k and high-k transistors. [Preview Abstract] |
Friday, October 6, 2006 2:54PM - 3:06PM |
OP1.00008: Developing a Capacitive Probe for Measuring Charging Effects on In-Vacuum Optics Dennis Ugolini, Robert McKinney Many gravitational-wave observatories such as LIGO use suspended fused-silica optics in a Michelson interferometer in an effort to measure oscillations in the curvature of space between 40 Hz and 1 kHz. One potential noise source in this frequency range is the buildup and motion of surface charge on the optics, which can generate fluctuating electric fields, interfere with position control, and attract dust to the optical surface. The noise contribution depends on the magnitude of charge buildup and the time constant for motion of deposited charge, neither of which is well understood \textit{in situ}. Many commercial probes exist that measure surface charge by modulating the capacitance between probe and sample through a vibrating probe tip. We have developed a probe that modulates capacitance with a tuning-fork optical chopper between probe and sample, chosen for vacuum compatibility and minimal cost. The probe has a resolution of 3 $\times $ 10$^{5} \quad e^{-}$\textit{/cm}$^{2}$ in air, which we expect will improve once the probe is moved to vacuum. We will report on efforts to characterize the probe's behavior and initial attempts at measuring the charging time constant. [Preview Abstract] |
Friday, October 6, 2006 3:06PM - 3:18PM |
OP1.00009: Recent development of Second-Harmonic Generation in Quantum Cascade Laser Feng Xie, Alexey Belyanin, Dongxia Qu, Gary Shu, Claire Gmachl Quantum cascade laser (QCL) has been rapidly developed in the recent decade. Integration of second harmonic generation (SHG) within the QCL enables this realization of a 3$\sim $5$\mu $m laser. In this talk, recent progress on SHG QCL (D3056) will be presented. The D3056 is designed to combine the resonant SHG and pump lasing within the same active region, working at 8.5$\mu $m (fundamental laser) and 4.2$\mu $m (SH signal). One interesting thing is that the linear-to-nonlinear power conversion efficiency $\eta $ increased with increasing electrical current. A Couple of explanations are discussed. One is that a multi-set of three-level systems was formed due to the significant change of dipole moments between some electron energy states for various applied electrical field. The other one is that increasing of electron population at upper lasing level caused the increase of nonlinear susceptibility. Moreover, lasing at both current polarities of the D3056 is a beneficial side effect of this active region design. [Preview Abstract] |
Friday, October 6, 2006 3:18PM - 3:30PM |
OP1.00010: Microwave Initiated Atomic Spectra from Select Atomic Species Aman Anand, James Roberts, Don Henley, Timothy Imholt, Jai Dahiya Isotopes of gaseous Helium ($^{3}$He and $^{4}$He) were admitted into the vacuum system at various pressures and allowed to stabilize. Quantum states were then energized using a 2.45 GHz magnetron coupled to the gases by loose coupling. A residual gas analyzer Mode100 series manufactured by Stanford Research Systems was used to determine the mass of each species and an Ocean Optics Optical Spectrometer model collecting the light via an optic probe was used to collect the spectra and to characterize the spectroscopic peaks. The data collected from these isotopes represent characteristic spectral emission lines generated due to the transitions among discrete quantum energy levels. The data analysis, especially for atomic spectroscopy, becomes an extremely important tool in developing an understanding of the quantum levels active within each atom. In this paper is presented a summary of the analysis work that was done on two isotopes of helium. Data using both computational as well as theoretical techniques are presented. Traditional high voltage arc discharge data were taken for the gas species and these are compared with microwave stimulated atomic emissions. [Preview Abstract] |
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