Bulletin of the American Physical Society
11th Annual Meeting of the Northwest Section of APS
Volume 54, Number 6
Thursday–Saturday, May 14–16, 2009; Vancouver, BC, Canada
Session G1: Atomic, Molecular, and Optical Physics |
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Chair: Andrew Dawes, Pacific University Room: Irving Barber Learning Center 185 |
Saturday, May 16, 2009 1:30PM - 2:06PM |
G1.00001: New Light and New Science: Terahertz-Induced Extreme Nonlinear Optical Transients in Semiconductor Quantum Wells Invited Speaker: Interaction of THz radiation with condensed matter is a highly diverse subject. The wide spectrum of assorted phenomena ranges from the lattice vibrations and the intraband transitions in semiconductors to the dynamics of complex fluids, electron spins, and strongly correlated electrons. The unique and advanced techniques of THz spectroscopy are a powerful tool to explore the material properties inaccessible until recently. When strong THz pulses are applied to a semiconductor quantum- well system, time resolved optical measurements reveal remarkable quantum effects. The optical response of semiconductor quantum-wells displays excitonic resonances with a typical energy spacing of 1 to 100 meV. To directly access transitions between these resonances, one can apply electro- magnetic fields in the terahertz frequency range. The resulting quantum dynamics and associated nonlinear optical effects are of great interest. They both manifest fundamental physical processes, such as many-body interactions and Coulomb correlations; and also have broad applications for optoelectronic devices. We report an uncharted regime of THz excitations: quantum coherent transients of internal excitonic transitions in semiconductor QWs driven by ultrafast THz pulses. We employed a THz-pump and optical-probe technique to investigate time-resolved nonlinear optical effects induced by intense single-cycle THz pulses. The most distinctive feature of this approach is that we can observe the THz-induced effects with the temporal resolution of 0.1 ps, limited by the femtosecond laser pulse duration. [Preview Abstract] |
Saturday, May 16, 2009 2:06PM - 2:18PM |
G1.00002: Intense narrow band terahertz generation via type-II DFG in ZnTe Joe Tomaino, Andy Jameson, Jeremy Danielson, Yun-Shik Lee, K. Vodopyanov We developed a tabletop source of intense, tunable, and narrowband THz pulses using difference frequency generation (DFG) in a nonlinear crystal. The light source of the experiment was 800-nm, 100-fs pulses from a 1-kHz Ti:sapphire regenerative amplifier (Coherent Inc., Legend). The main portion of the optical power was used to generate strong narrowband THz pulses. A linear chirp was introduced to stretch the optical pump pulses to $\sim $4 ps. An optical setup split the pump beam into two, introduced a relative time delay, made them orthogonally polarized, and eventually recombined them to co-propagate. The two linearly-chirped and orthogonally-polarized optical beams produced narrowband THz radiation via type-II DFG in a 1-mm ZnTe crystal. The THz pulse energy was in the range of a few nJ, and the pulse duration was $\sim $3 ps. The maximum amplitude of the electric field reached $\sim $10 kV/cm. The central frequency of the spectrum is continuously tunable from 0.5 to 2.5 THz with a bandwidth of 0.2-0.5 THz. This technique can be easily integrated into time-resolved studies on terahertz-induced nonlinear effects with a subpicosecond resolution limited only by the transform-limited optical pulse duration. [Preview Abstract] |
Saturday, May 16, 2009 2:18PM - 2:30PM |
G1.00003: Terahertz Properties of an Organic Nonlinear Optical Crystal Andrew Jameson, Joseph Tomaino, Yun-Shik Lee, Ji-Youn Seo, O-Pil Kwon As a result of the findings that organic nonlinear crystals, e.g., DAST, have remarkably large nonlinear optical coefficients in the THz region, rigorous investigations have been conducted for efficient THz generation and detection using these material systems. We performed THz experiments on a new type of hydrogen-bonded organic nonlinear crystal, 2-[3-(4-hydroxystyryl)-5,5-dimethylcyclohex-2-enylidene]malononitrile (OH1). First, we demonstrated the generation of strong single-cycle THz pulses using optical rectification in an OH1 crystal. The output power reached up to a few microwatts. Second, we measured transmission spectra of the sample in the THz region using THz time-domain spectroscopy. We indentified several vibrational resonances from 0.8-2.1 THz. These preliminary experimental data on OH1 show much promise for future use as a THz source, as well as being readily adaptable to many nonlinear studies because of its high nonlinearity and easily accessible vibrational resonances in the THz region. [Preview Abstract] |
Saturday, May 16, 2009 2:30PM - 2:42PM |
G1.00004: Finite-size and confinement effects in spin-polarized trapped Fermi gases Mark Ku, Jens Braun, Achim Schwenk We calculate the energy of a single fermion interacting resonantly with a Fermi sea of different-species fermions in anisotropic traps, and show that finite particle numbers and the trap geometry impact the phase structure and the critical polarization. Our findings contribute to understanding some experimental discrepancies in spin-polarized Fermi gases as finite-size and confinement effects. [Preview Abstract] |
Saturday, May 16, 2009 2:42PM - 2:54PM |
G1.00005: Hydrogen and Helium atoms in strong magnetic fields Anand Thirumalai, Jeremy Heyl The energy levels of hydrogen and helium atoms in strong magnetic fields are calculated in this study. The current work contains accurate estimates of the binding energies of the first few low-lying states of these systems that are improvements upon previous estimates. The methodology involves computing the eigenvalues and eigenvectors of the generalized two-dimensional Hartree-Fock partial differential equations for these one- and two-electron systems in a self-consistent manner. The method described herein is applicable to calculations of atomic structure in magnetic fields of arbitrary strength as it exploits the natural symmetries of the problem without assumptions of any basis functions for expressing the wave functions of the electrons or the commonly employed adiabatic approximation. The method is found to be readily extendable to systems with more than two electrons. [Preview Abstract] |
Saturday, May 16, 2009 2:54PM - 3:14PM |
G1.00006: BREAK
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Saturday, May 16, 2009 3:14PM - 3:50PM |
G1.00007: Optical antennas for nanoscale imaging and spectroscopy: probing matter on its natural time and length scales Invited Speaker: The natural time- and length-scales of the elementary excitations in matter define a new regime of ultrafast vibration and electron dynamics as the dimensions of the medium shrink into the 1 to 100 nm range. To achieve the required femtosecond temporal and nanometer spatial resolution we take advantage of the optical antenna properties of nanoscopic metal tips. They provide the necessary local field enhancement and spatial confinement for what became known as scattering-type near-field optical microscopy. I will discuss several examples of linear and nonlinear spectroscopic imaging in the visible and infrared spectral region providing direct access to the molecular vibrational dynamics in organic nanocomposites, the ultrafast electronic decoherence of plasmonic nanostrucutres, or the phase behavior of complex materials such as transition metal oxides. I will also discuss new concepts for the rational design of nanoconfined light sources for spectroscopy and imaging. [Preview Abstract] |
Saturday, May 16, 2009 3:50PM - 4:02PM |
G1.00008: Ultrashort laser pulse absorption and target heating Sergey Bochkarev, Wojciech Rozmus, Andrei Brantov, Valery Bychenkov, Mark Sherlock A theory of ultrashort laser pulse absorption in dense targets is important for modeling of basic physics and applications of short laser pulse plasma interactions. Recent experiments have challenged our understanding of absorption processes by showing dramatic increases of absorbed laser energy fraction at relativistic intensities. An important issue is the question how and with what efficiency the laser energy could be absorbed in dense plasmas. We describe a model of ultrashort laser pulse absorption which includes linear absorption and thermal transport into dense plasma. Plasma dielectric function in our model describes collisional and collisionless absorption mechanisms including the effect of electron-electron collisions. Thermal transport is modeled using nonlocal expressions that are valid in the weakly collisional regime. We also compare our results with Vlasov-Fokker-Planck simulations. [Preview Abstract] |
Saturday, May 16, 2009 4:02PM - 4:14PM |
G1.00009: An intuitive approach to broadband dispersion measurements in high finesse optical cavities T.J. Hammond, Arthur K. Mills, David J. Jones We present a simple method to determine group delay dispersion by measuring the resonance condition of a high finesse optical cavity across a broad bandwidth using a femtosecond laser frequency comb. More generally, our technique measures the complete wavelength dependence of the cavity dispersion including higher order dispersion. This intuitive method is simply analyzed, and it is a powerful tool that can be used to extend well-understood single frequency optical resonator concepts to the case of broadband excitation. Accurate measurement of the dispersion of high finesse cavities is key to designing passive enhancement cavities for use in extreme ultraviolet light generation using high harmonic generation and other applications of extreme nonlinear optics. In this talk we will present the background behind our technique and experimental results, including the accuracy in determining group delay dispersion properties of several well-characterized materials. [Preview Abstract] |
Saturday, May 16, 2009 4:14PM - 4:26PM |
G1.00010: Characterizing Galbumin as a high molecular weight contrast agent in MRI - A novel dual contrast agent protocol Firas Moosvi, Stefan Reinsberg, Jennifer Baker In studying cancer and tumours, traditional biochemical methods call for analyzing frozen cross sections of tumour tissues, staining and then fluorescently imaging them at high resolution. While this method has served its purpose for decades, situations and conditions are arising that require dynamic imaging in live animals. Recent advances in the field of Biophysics have allowed researchers the ability to correlate images taken with Magnetic Resonance Imaging (MRI) to those using high- resolution fluorescent microscopy. While live imaging is possible using MRI, it is certainly not possible to reproduce much of the biologically relevant data acquired by fluorescent microscopy. In this proposal, we set the stage for the biological problem, cover some basic tumour biology then outline the basic principles of imaging with NMR. Finally, we characterize the use of a new contrast agent, Galbumin, to conduct a pilot study for a new class of animal MRI experiments.Finally, we present a novel protocol for a dual contrast agent MR protocol to extract permeability and flow information to improve characterization of drug delivery. Our over-arching goal is to use the live imaging capabilities of MR, and combine them with traditional fluorescent microscopy techniques to get a more accurate biological picture of a tumour. [Preview Abstract] |
Saturday, May 16, 2009 4:26PM - 4:38PM |
G1.00011: Calibration of holographic optical tweezers for force measurements on biomaterials Astrid van der Horst, Nancy Forde Holographic optical tweezers (HOTs) modify the phase of a laser beam to create and dynamically position multiple optical traps independently in 3D; refractive micrometer-sized particles can be held in these traps to function as probing handles. HOTs offer the flexibility needed to probe the mechanics of complex systems such as cells or protein networks. Thus far, however, HOTs have not found wide use in biophysics, in large part due to lack of evidence as to how exerted forces vary as the positions of HOT traps are changed. To perform quantitative force measurements, parameters such as trap stiffness, range of trap steering, and minimum step size are of key importance. We find for our HOT setup that stiffness does not change significantly over a range of $\sim$25$\mu$m. In addition, we control and detect, using high-speed ($>$kHz) camera imaging, trap displacements to $\sim$1nm. Our results suggest that after full characterization HOTs can be successfully employed in quantitative experiments on biomaterials, e.g., probing elastomeric properties of structural protein networks. [Preview Abstract] |
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