Bulletin of the American Physical Society
Joint Fall 2013 Meeting of the Texas Sections of the APS, AAPT, and Zone 13 of the SPS
Volume 58, Number 10
Thursday–Saturday, October 10–12, 2013; Brownsville, Texas
Session B2: Atomic, Molecular and Optical Physics |
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Chair: Malik Rakhmanov, University of Texas at Brownsville Room: EDBC 1.508 |
Friday, October 11, 2013 10:30AM - 10:42AM |
B2.00001: Discharging Fused Silica Optics Occluded by an Electrostatic Drive Dennis Ugolini Charge accumulation on test masses is a potentially limiting noise source for gravitational-wave interferometers, and may occur due to exposure to an electrostatic drive (ESD) in modern test mass suspensions. In this talk I will show that an ESD can cause charge accumulation on a fused silica test mass at a rate of 8 * 10$^{\mathrm{-16}}$ C/cm$^{\mathrm{2}}$/hr. I will also describe a charge mitigation system consisting of a stream of nitrogen ionized by copper feedthrough pins at 3750 VAC. This system can neutralize positive and negative charge from 10$^{\mathrm{-11}}$ C/cm$^{\mathrm{2}}$ to 3 * 10$^{\mathrm{-14}}$ C/cm$^{\mathrm{2}}$ in under two hours. [Preview Abstract] |
Friday, October 11, 2013 10:42AM - 10:54AM |
B2.00002: Spectroscopic and Theoretical Determination of the Structure of 2,6-Difluoropyridine in Its Ground and Excited Electronic States Jaan Laane, Hong-Li Sheu, Sunghwan Kim The infrared and Raman spectra of 2,6-difluoropyridine (26DFPy) along with \textit{ab initio} and DFT computations have been used to assign the vibrations of the molecule in its S$_{0}$ electronic ground state and to calculate its structure. The ultraviolet absorption spectrum showed the electronic transition to the S$_{1}(\pi $,$\pi $*) state to be at 37,820.2 cm$^{-1}$. With the aid of \textit{ab initio} computations the vibrational frequencies for this excited state were also determined. TD-B3LYP and CASSCF computations for the excited states were carried out to calculate the structures for the S$_{1}(\pi $,$\pi $*) and S$_{2}$(n,$\pi $*) excited states. The CASSCF results predict that the S$_{1}(\pi $,$\pi $*) state is planar and the S$_{2}$(n,$\pi $*) state has a barrier to planarity of 256 cm$^{-1}$. The TD-B3LYP computations predict a barrier of 124 cm$^{-1}$ for the S$_{1}(\pi $,$\pi $*) states, but the experimental results support the planar structure. Hypothetical models for the ring-puckering potential energy function were calculated for both electronic excited states to show the predicted quantum states. The changes in the vibrational frequencies in the two excited states reflect the weaker $\pi $ bonding within the pyridine ring. [Preview Abstract] |
Friday, October 11, 2013 10:54AM - 11:06AM |
B2.00003: Calculating Relativistic Atomic and Molecular Properties Using Monte Carlo Methods Steve Alexander, R.L. Coldwell There are a number of computational methods that can be used to calculate the energies and properties of nonrelativistic atoms and molecules. Fully relativistic calculations of these systems are much less common and more complicated. In part, this is because each relativistic particle generates four coupled components and the presence of negative energy states prohibits the use of most variational techniques. In this talk I will describe how variational Monte Carlo methods can be used to calculate the energy and properties of fully relativistic atoms and molecules. Results for both one electron and two electron systems will be presented. [Preview Abstract] |
Friday, October 11, 2013 11:06AM - 11:18AM |
B2.00004: Frequency stabilization of a Planar Waveguide External Cavity Laser Oliver Puncken, Gregorio Tellez, Steven Shoen, Volker Quetschke Narrow linewidths and high stability in frequency and intensity are important laser properties in fields as optical communication, laser cooling, and atomic frequency standards. In the context of space based gravitational wave astronomy, it is assumed that the lasers must have a frequency stability of 30 $Hz/\sqrt{Hz}$ over a frequency-band from 3 mHz to 30 mHz. Planar-Waveguide External-Cavity lasers might provide an alternative to nonplanar ring oscillators or fiber lasers. To achieve this requirement, frequency stabilization to an external reference is necessary. We present our initial experimental results of the intensity and frequency stabilization setup for a Planar Waveguide External Cavity Laser at 1550 nm to a high finesse ultra low expansion (ULE) cavity. The stabilization to the sub-Hertz level can be accomplished by using a Pound-Drever-Hall stabilization scheme. The injection current is used as a fast actuator and the laser temperature as a compensator for slow drifts. The setup is isolated from the environment by using a radiative shield inside a vacuum tank in order to decouple it from thermal and acoustical disturbances. We build two identical setups, which allows for measuring the sum frequency noise of the systems by investigating the beat note. [Preview Abstract] |
Friday, October 11, 2013 11:18AM - 11:30AM |
B2.00005: Experimental and Theoretical Determination of the Structures and Molecular Vibrations of Benzocyclobutane in Its Ground and Excited Electronic States Jaan Laane, Esther Ocola, Hee Won Shin, Sunghwan Kim The infrared and Raman spectra of vapor-phase and liquid-phase benzocyclobutane (BCB) have been recorded and assigned. The structure and molecular vibrations of BCB were also computed using theoretical calculations. The ring-puckering, ring-twisting, and ring-flapping vibrations were of particular interest as these reflect the rigidity of the bicyclic ring system. The fluorescence excitation spectra of jet-cooled BCB have also been recorded and together with its ultraviolet absorption spectra were used to assign the vibrational frequencies for this molecule in its S$_{1}(\pi $,$\pi $*) electronic excited state. Theoretical calculations were carried out to compute the structure of the molecule in its excited state and this was compared to that of the molecule in its electronic ground state as well as to the structures of five related molecules in their S$_{0}$ and S$_{1}(\pi $,$\pi $*) electronic states. In each case the decreased $\pi $ bonding resulted in longer carbon-carbon bonds in the benzene ring in the electronic excited states. The vibrational frequencies in the electronic excited state were readily assigned and these were compared to the ground state and to the frequencies of similar molecules. The decreases in the frequencies of the out-of-plane skeletal modes also reflect the increased floppiness of these bicyclic molecules in their S$_{1}(\pi $,$\pi $*) excited state. [Preview Abstract] |
Friday, October 11, 2013 11:30AM - 11:42AM |
B2.00006: Transport coefficients from the Boson Uehling-Uhlenbeck Equation Erich Gust, Linda Reichl We derive microscopic expressions for the bulk viscosity, shear viscosity and thermal conductivity of a quantum degenerate Bose gas above $T_C$, the critical temperature for Bose-Einstein condensation. The gas interacts via a contact potential and is described by the Uehling-Uhlenbeck equation. To derive the transport coefficients, we use Rayleigh-Schrodinger perturbation theory rather than the Chapman-Enskog approach. This approach illuminates the link between transport coefficients and eigenvalues of the collision operator. We find that a method of summing the second order contributions using the fact that the relaxation rates have a known limit improves the accuracy of the computations. We numerically compute the shear viscosity and thermal conductivity for any boson gas that interacts via a contact potential. We find that the bulk viscosity remains identically zero as it is for the classical case. [Preview Abstract] |
Friday, October 11, 2013 11:42AM - 11:54AM |
B2.00007: Modeling of Error Signal and Locking of Laser to Photonic Crystal Nanocavity Darkhan Tuyenbayev, Benjamin Frost, Malik Rakhmanov In many applications of silicon nanophotonics, lasers are brought to resonate in photonic crystal nanocavities. We analyze the possibility of locking a laser to a photonic crystal nanocavity using computer simulations. The nanocavity is formed by a single point defect in a 2-d square lattice of holes in a silicon slab. We couple light to the cavity through a line-defect waveguide and detect the leakage light from the cavity through an auxiliary waveguide. The resonance is achieved by choosing the frequency at the guided mode within the band gap of the photonic crystal. Detuning the light from perfect resonance gives rise to intensity beats in two waveguides which generate the error signal. This error signal is then used in feedback control loop to lock the laser to the cavity. The calculations are performed with the Finite-Difference Time-Domain (FDTD) model and the numerical analysis of the photonic band structure. [Preview Abstract] |
Friday, October 11, 2013 11:54AM - 12:06PM |
B2.00008: Solutions of the Harmonic Oscillator Equation in a B-polynomial basis Muhammad Bhatti A method to construct approximate solutions for a quantum mechanical system has been introduced in a Bernstein-polynomial (B-polynomial) basis. The B-polynomial-Galerkin method is applied to produce the energy spectrum of quantum harmonic oscillator equation. The discrete eigenstates are produced after applying the initial condition to the generalized eigenvalue problem which was constructed from the exact analytic matrix elements in the basis. The numerical discrete eigenvalues and the corresponding eigenstates are in excellent agreement with the exact results of the harmonic oscillator. However, the accuracy of the results depends on the number of B-polynomials chosen to construct the approximate solutions. To check the quality of the spectrum and the wave functions, the resulting basis set is used to evaluate the Thomas-Reiche-Kuhn (TRK) sum rules. In addition, perturbations through 5$^{\mathrm{th}}$ order are calculated to first excited state of harmonic oscillator using a perturbation potential and excellent agreement has been observed with exact results. [Preview Abstract] |
Friday, October 11, 2013 12:06PM - 12:18PM |
B2.00009: A Dual Locking Scheme for Measurement of Long-Term Stability of a Triangular Ring Resonator Johnathan Aguilar, Oliver Puncken, Malik Rakhmanov The triangular ring resonator is an optical cavity that filters the higher order Hermite-Gaussian modes of a laser beam. Once locked to the fundamental mode, the resonator behaves as a Fabry-Perot interferometer. We analyze the sensitivity of the triangular ring resonator using a dual-locking scheme based on the Pound-Drever-Hall (PDH) method. The resonator is locked to the fundamental mode of a 1064-nm Nd:YAG Laser using the PDH error signal to drive the piezo-mounted curved mirror of the resonator. The laser is then locked to the transition line of a stable atomic reference (Iodine vapor cell). Once the frequency of the laser is stabilized, the PDH error signal pertains only to the intrinsic noise of the resonator. The proposed scheme is intended for measurement of long-term stability of the ring resonator and its limiting noise performance at very low frequencies. [Preview Abstract] |
Friday, October 11, 2013 12:18PM - 12:30PM |
B2.00010: Theoretical Analysis of an Interferometer with Variable Signal Recycling Mirror Artemiy Bogdanovskiy, Malik Rakhmanov Searches for gravitational waves are now conducted with Laser Interferometer Gravitational-wave Observatory (LIGO) which utilizes Michelson interferometers with 4-km arm lengths. To achieve the desired sensitivity the detectors are enhanced with Fabry-Perot resonators in the interferometer arms. Currently, the detectors are undergoing an upgrade to the Advanced LIGO configuration which will involve the Signal Recycling mirror for further increase of their sensitivity. In the present design, the Signal Recycling mirror has fixed reflectivity which leads to fixed detection bandwidth. Future gravitational wave detectors will benefit from variable reflectivity of the Signal Recycling mirror which allows controlled bandwidth. To understand the performance of such a detector we calculate its transfer functions in terms of mirror parameters. We analyze ways to tune its peak sensitivity and its detection bandwidth using the variable signal recycling mirror. The results can be used in future work on prototyping such tunable detectors. [Preview Abstract] |
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