Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session G41: Attosecond Physics and Optics |
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Sponsoring Units: DAMOP Chair: Stephen Eckel, National Institute of Standards and Technology Room: 350 |
Tuesday, March 19, 2013 11:15AM - 11:27AM |
G41.00001: Simulated Photoelectron-Based Imaging of Localized Surface Plasmons with Attosecond Resolution James Prell, Lauren Borja, Andrey Gandman, Desire Whitmore, Daniel Neumark, Stephen Leone Simulations of proposed photoelectron streaking experiments in the presence of an oscillating plasmon field are presented. The results indicate that localized surface plasmon dephasing can be imaged with attosecond resolution using electron time-of-flight (TOF) or velocity map imaging (VMI) techniques. In the simulation, localized surface plasmons are excited in metal nanoparticles by a few-cycle infrared or visible laser pulse. Using time-delayed single, isolated attosecond x-ray pulses, electrons are photoemitted from the metallic nanoparticles and streaked by both the plasmon and laser electric fields. The effects of these two fields in the streaking spectra and images can be separated so that the temporal evolution of the plasmon electric field can be directly extracted. The plasmon electric field induces a broadening of the photoelectron speed distribution with an envelope directly proportional to that of the plasmon dipole moment. Plasmon-induced oscillation of the angular distribution in VMI is predicted to report the spatial distribution of the plasmon electric field for nanoparticles with high aspect ratios. The simulations indicate that these techniques can be used to map plasmon dynamics with unprecedented temporal resolution. [Preview Abstract] |
Tuesday, March 19, 2013 11:27AM - 11:39AM |
G41.00002: Metal nanofilm in strong ultrafast optical fields: subcycle Bloch oscillations Vadym Apalkov, Mark Stockman We predict theoretically that a metal nanofilm subjected to an ultrashort optical pulse of a high field amplitude $\sim 3$ V/\AA $~$ shows semimetal behavior. At such high pulse intensity, the reflectivity of metal nanofilm is greatly reduced, while the transmissivity and the optical field inside the metal are greatly increased. The temporal profiles of the optical fields are predicted to exhibit pronounced subcycle oscillations which are attributed to the Bloch oscillations and formation of the Wannier-Stark ladder of electronic states. These effects are promising for applications as nanoplasmonic modulators and field-effect transistors with petahertz bandwidth. [Preview Abstract] |
Tuesday, March 19, 2013 11:39AM - 12:15PM |
G41.00003: Attosecond Streaking Chronoscopy of Surfaces Invited Speaker: Joachim Burgdoerfer With the advent of sub-femtosecond ultrashort XUV pulses and of phase-stabilized IR pulses with sub-cycle time resolution, novel pathways have been opened up for studying time-resolved electronic quantum dynamics on the attosecond scale. These experiments pose challenges for theory: How do short pulses interact with matter? Which novel information can be extracted from time-resolved spectroscopies that cannot be gained from precision experiments in the spectral domain? In this talk we discuss attosecond chronoscopy by streaking photoelectron emission from solid surfaces. Experimental photoemission data reveal a time delay between conduction electrons and core electrons on the $\sim$50 attosecond scale. We show that the temporal information accessible for such a many-electron system in the condensed phase includes both the coherent wavepacket dynamics characterized by the Eisenbud-Wigner-Smith (EWS) time delay as well as decohering processes in transport and relaxation. Extensions to nanostructures will be discussed. [Preview Abstract] |
Tuesday, March 19, 2013 12:15PM - 12:27PM |
G41.00004: Strong-Field Emission From High Aspect Ratio Si Emitter Arrays Phillip Keathley, Michael Swanwick, Alexander Sell, William Putnam, Stephen Guerrera, Luis Vel\'asquez-Garc\'Ia, Franz K\"artner We discuss photoelectron emission from an arrays of high aspect ratio, sharp Si emitters both experimentally and theoretically. The structures are prepared from highly doped single-crystal silicon having a pencil-like shape with end radii of curvature of around 10 nm. The tips were illuminated at a grazing incidence of roughly 84deg.with a laser pulse having a center wavelength of 800 nm, and a pulse duration of 35 fs from a regenerative amplifier system. Native oxide coated Si tips were characterized using a time of flight (TOF) electron energy spectrometer. An annealing process was observed, resulting in a red shift of the energy spectra along with an increased electron yield. Total current yield from samples having the oxide stripped were also studied. Apeak total emission of 0.68 pC/bunch, corresponding to around 1.5x10$^3$ electrons/tip/pulse was observed at a DC bias of 70 V . Both spectral and current characterization results are consistent with a stong-field photoemission process at the surface of the tip apex. [Preview Abstract] |
Tuesday, March 19, 2013 12:27PM - 12:39PM |
G41.00005: Laser Beam Shaping For Lithography on Inclined and Curved Surfaces Using a liquid crystal Spatial Light Modulator Javad R. Gatabi, Wilhelmus Geerts, Dan Tamir, Kumar Pandey An exposure tool for lithography on non-flat substrates that includes a real time photoresist thickness and surface topography monitor is under development at Texas State University. Exposure dose and focusing are corrected on curved parts of the sample using novel laser beam shaping techniques: two approaches using a Holoeye liquid crystal spatial light modulator (LC-SLM) are being investigated: (1) the implementation of multiple lenses with different focal lengths to split the beam into several parts and keeping each part in focus depending on sample topography; (2) the implementation of a tilted lens function resulting in a tilt of the image plane. Image quality is limited by quantization aberration, caused by the phase modulator's bit depth limitation, and pixelation aberration, caused by the modulator's pixel size. A statistical analysis on lenses with different focal lengths provides a detailed description of the mentioned aberrations. The image quality, i.e. resolution and contrast of both techniques, are determined from developed photoresist patterns on curved samples and compared to the theory. [Preview Abstract] |
Tuesday, March 19, 2013 12:39PM - 12:51PM |
G41.00006: Imaging the signals emitted by multiple sources originating from a turbid medium Gabriel Cwilich, Juan Jose Saenz, Luis Froufe Perez We studied the problem of spatially closely positioned sources which emit waves inside a turbid medium, through fluorescence or other mechanisms. While for many of the traditional imaging methods, including FRET, the disorder might impose an insurmountable obstacle for the detections of the sources, the interference of the waves in the case of multiple scattering, gives raise, due the coherent propagation of the signals at the mesoscopic scale , to important effects both in the correlations and the fluctuations of the intensity being detected at a point lying outside the medium. The information obtained that way can be used to monitor the displacement of the sources and their degree of coherence even at scales below the wavelength of the radiation being emitted. [Preview Abstract] |
Tuesday, March 19, 2013 12:51PM - 1:27PM |
G41.00007: Attosecond view of the photoelectric effect and optical-field-induced current in dielectrics Invited Speaker: Ralph Ernstorfer Fundamental electronic processes in condensed matter like electron transport on atomic length scales, the plasmonic response in metals or the dielectric response in insulators occur on attosecond time scales. In the first part of my talk, I discuss how a streak camera operating at optical frequencies provides a time-resolved view of the photoelectric effect [1]. Photoelectrons emitted from metal surfaces by an attosecond extreme ultraviolet laser pulse are time-stamped by a few-cycle visible/near-infrared laser pulse. This technique allows for measuring the relative emission time of valence and core electrons with a precision of tens of attoseconds, thereby addressing the intrinsic dynamics of the photoemission. I present recent studies of a free-electron metal [2] as well as of oxygen-covered tungsten single crystals. The origin of the observed attosecond delays in the emission of photoelectrons from different initial states is discussed. In the second part of the talk, I report on electric current in dielectrics induced and controlled by ultrashort optical fields [3]. For very short periods of time, electric fields exceeding 10 V/nm, i.e. fields significantly beyond the threshold for dc dielectric breakdown, can be applied to insulators. In this regime, insulators exhibit a highly nonlinear dielectric response, resulting in an increase in conductivity by many orders of magnitude. Applying 1.5-cycle laser pulses to unbiased metal-dielectric-metal nanogaps, we demonstrate the generation of directly measurable photocurrents whose magnitude and directionality can be controlled with the carrier-envelope phase of the laser pulse, i.e. by the shape of the laser electric field. Such currents can be switched on and off on sub-femtosecond timescales as evidenced by employing two cross-polarized and time-delayed pulses. The ultrafast field-controlled current generation in a dielectric nanostructure may represent a first step towards the realization of optical-field-controlled electronics.\\[4pt] References:\\[0pt] [1] A.L. Cavalieri et al., Nature 449, 1029 (2007).\\[0pt] [2] S. Neppl et al., Phys. Rev. Lett. 109, 087401 (2012). \\[0pt] [3] A. Schiffrin et al., Nature (2013), doi:10.1038/nature11567. [Preview Abstract] |
Tuesday, March 19, 2013 1:27PM - 1:39PM |
G41.00008: Nondiffracting accelerating wave packets beyond the paraxial limit Peng Zhang, Yi Hu, Tongcang Li, Drake Cannan, Xiaobo Yin, Roberto Morandotti, Zhigang Chen, Xiang Zhang Self-accelerating Airy wave packets have stimulated rapidly growing research interest in the past five years. However, optical Airy beams are inherently subjected to the paraxial limit. Here, we demonstrate both theoretically and experimentally linear and nonlinear self-accelerating beams propagating along circular trajectories beyond the paraxial approximation. Such nonparaxial accelerating beams are exact solutions of the Helmholtz equation. Furthermore, we introduce and demonstrate nonparaxial Mathieu and Weber accelerating beams, generalizing the concept of all previously found accelerating wave packets. We show that such beams bend into large angles along elliptical or parabolic trajectories but still retain nondiffracting and self-healing capabilities. The circular nonparaxial accelerating beams can be considered as a special case of the Mathieu accelerating beams, while an Airy beam is only a special case of the Weber beams at the paraxial limit. Not only do generalized nonparaxial accelerating wave packets open up many possibilities of beam engineering for applications, but the fundamental concept developed here can be applied to other linear wave systems in nature, ranging from electromagnetic and elastic waves to matter waves. [Preview Abstract] |
Tuesday, March 19, 2013 1:39PM - 1:51PM |
G41.00009: Mapping of focused Laguerre-Gauss beams Jose R. Rios Leite, Vasily Klimov, Martial Ducloy, Daniel Bloch We study the detection of propagating optical fields bearing axial symmetry in the situation of an extreme focusing, when the paraxial approximation no longer holds. The results, obtained by general arguments based upon the vectorial nature of electromagnetic fields, show the rapid spatial variations of fields with ``complicated'' spatial structure [1]. Laguerre-Gauss beam, notably beams bearing a l = 2 orbital angular momentum for which a magnetic field and a gradient of the electric field are present on axis have been examined in their behavior upon an atomic size light detector sensitive to quadrupole electric transitions as well as to magnetic dipole transitions. nd apply it to the case of a Laguerre-Gauss beam.We detail how the mapping of such a beam depends on the nature and on the specific orientation of the detector. We also show that the interplay of mixing of polarization and topological charge, respectively associated to spin and orbital momentum when the paraxial polarization holds, modifies the apparent size of the beam in the focal plane.\\[0pt] [1]. V. Klimov, M. Ducloy, D. Bloch and JR Rios Leite, Phys. Rev. A 85, 053834 (2012). [Preview Abstract] |
Tuesday, March 19, 2013 1:51PM - 2:03PM |
G41.00010: Photonic temperature sensor based on microring resonators Haitan Xu, Zeeshan Ahmed, Mohammad Hafezi, Jingyun Fan, Gregory Strouse, Alan Migdall, Jacob Taylor Temperature needs to be controlled accurately and precisely in various areas, yet it is one of the most inaccurately measured physical quantities. We consider a new measurement method for temperature using the thermal response of a microring resonator built using Silicon-on-Insulator. The temperature-dependence of the index refraction maps temperature to the resonance frequency of the resonator, which can be measured with higher precision. We study the resolution and accuracy of our device, as well as future challenges for this approach for temperature metrology. [Preview Abstract] |
Tuesday, March 19, 2013 2:03PM - 2:15PM |
G41.00011: A new bound on excess frequency noise in second harmonic generation in PPKTP at the $10^{-19}$ level David Yeaton-Massey, Rana Adhikari Several experiments at the forefront of precision metrology and frequency standards use optical harmonic generation in their experiments. These include iodine stabilized Nd:YAG lasers, optical frequency combs, measurement of optical frequency ratios, and precision atomic spectroscopy. We present an experimental bound on the relative frequency fluctuations introduced in the nonlinear second harmonic generation process using PPKTP to double a 1064nm Nd:YAG laser. We report a measured amplitude spectral density of frequency noise with total RMS frequency deviation of 3mHz and a minimum value of 20 $\mu$Hz/Hz$^{1/2}$ over 250 seconds with a measurement bandwidth of 128 Hz, corresponding to an Allan deviation of $10^{-19}$ at 20 seconds. [Preview Abstract] |
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