Bulletin of the American Physical Society
APS March Meeting 2010
Volume 55, Number 2
Monday–Friday, March 15–19, 2010; Portland, Oregon
Session Q4: Celebrating 50 Years of Lasers in Condensed Matter Physics: Surfaces, Imaging & Technology |
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Sponsoring Units: DPOLY Chair: Marcus Cicerone, National Institute of Standards and Technology Room: Oregon Ballroom 204 |
Wednesday, March 17, 2010 11:15AM - 11:51AM |
Q4.00001: Nonlinear Optical Spectroscopy as a Unique Probe for Surfaces of Liquids, Polymers and Solids Invited Speaker: Second-order nonlinear optical spectroscopy has evolved into a highly surface-specific spectroscopic probe for investigation of surfaces and interfaces. Currently, it is the only technique that can yield surface vibrational or phonon spectra of liquids, polymers, and even solids. Applications of the technique to water, for example, have provided valuable information about structures of various water interfaces not achievable by other means. The same has been found with applications to polymers and crystalline solids. This work was supported by NSF WaterCAMPWS and DOE. [Preview Abstract] |
Wednesday, March 17, 2010 11:51AM - 12:27PM |
Q4.00002: Fourier Imaging Correlation Spectroscopy for Studies of Sub-Cellular Dynamics and Biomolecular Conformation Transition Pathways Invited Speaker: Novel high signal-to-noise spectroscopic experiments that probe the dynamics of fluorescently labeled macromolecules have the potential to reveal complex intracellular biochemical mechanisms, or the slow relaxations of soft matter systems. Fourier imaging correlation spectroscopy (FICS) is a phase-selective approach to fluorescence fluctuation spectroscopy that employs a unique route to elevate signal levels while acquiring detailed information about microscopic coordinate trajectories. In this talk, I will illustrate the broad applicability of this approach by discussing two recent studies. The anomalous sub-diffusive dynamics of mitochondria in budding yeast are characterized using FICS, and provide detailed, length-scale dependent information about the influence of specific cytoskeletal elements on the movements of this organelle. We find that non-equilibrium forces associated with actin polymerization lead to a 1.5-fold enhancement of the long-time mitochondrial diffusion coefficient, and a transient sub-diffusive temporal scaling of the mean-square displacement. These non-equilibrium dynamics are a predominant factor in driving mitochondrial transport. In another set of experiments, polarization-modulated FICS simultaneously captures information about the internal conformation fluctuations and molecular translational dynamics of the fluorescent protein DsRed. By implementing a four-point correlation analysis, we construct two-dimensional spectral densities and joint distribution functions that determine temporal correlations of center-of-mass and anisotropy coordinates over successive time intervals. These four-point functions reveal statistically meaningful transition pathways between different optical conformations of the DsRed protein. The FICS method is well suited to investigate the dynamics of a broad range of heterogeneous systems, which include the molecular motions of glass forming liquids. [Preview Abstract] |
Wednesday, March 17, 2010 12:27PM - 1:03PM |
Q4.00003: Exploring the Underlying Biophysics of Eukaryotic Plasma Membrane Asymmetry by Sum-Frequency Vibrational Spectroscopy Invited Speaker: A central issue in molecular biology is the movement of lipids across the cellular membrane. The translocation of lipids is involved in cell apoptosis, the viral infection of living cells, the functioning of antibiotics, antiseptics and drugs, and the regulation and growth of cells. There have been a number of studies attempting to find the putative proteins responsive for lipid transbilayer movement in eukaryotic cells. This has led to a large number of theories about the mechanism of transbilayer movement of lipids in cellular systems and the physical process by which lipid compositional asymmetry in the plasma membrane of eukaryotic cells is maintained. Using methods of classical surface chemistry coupled with nonlinear optical methods, we have developed a novel analytical approach, using sum-frequency vibrational spectroscopy (SFVS), to selectively probe lipid compositional asymmetry in a planar supported lipid bilayer. This new method allows for the detection of lipid flip-flop kinetics and compositional asymmetry without the need for a fluorescent or spin-labeled lipid species. The effect of lipid composition, headgroup and fatty acid chemical structure, on the rate and thermodynamics of lipid transbilayer migration and the electrostatic induction of lipid asymmetry will be discussed. [Preview Abstract] |
Wednesday, March 17, 2010 1:03PM - 1:39PM |
Q4.00004: Pushing the Envelope in Biological Imaging Invited Speaker: Optical microscopy has been instrumental in studies of the structure and function of biological systems for centuries. However, many questions at the forefront of molecular, cellular, and neurobiology remain beyond its current capabilities. I will discuss efforts in my group to extend these capabilities in areas such as superresolution optics, photodamage mediation, high speed volumetric imaging, and deep tissue imaging. [Preview Abstract] |
Wednesday, March 17, 2010 1:39PM - 2:15PM |
Q4.00005: 3D Photonic Metamaterials Made by Direct Laser Writing Invited Speaker: Over the last decade, direct laser writing (DLW) has matured from a laboratory curiosity to a commercially available technology that can be viewed as the three-dimensional analogue of two-dimensional electron-beam lithography. In DLW, lateral line widths down to about 100 nm (at 800 nm laser wavelength) have become routine. Even diffraction-unlimited DLW using stimulated emission depletion (STED) appears to be in reach. In this talk, we emphasize applications of DLW regarding fabrication of three-dimensional metamaterials operating at optical frequencies. Recent examples are (i) gold-helix metamaterials that can serve as compact, broadband circular polarizers, (ii) bi-chiral helical structures, and (iii) complex three-dimensional transformation-optics nanostructures (carpet cloaks). [Preview Abstract] |
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