Bulletin of the American Physical Society
Annual Meeting of the Four Corners Section of the APS
Volume 59, Number 11
Friday–Saturday, October 17–18, 2014; Orem, Utah
Session D6: Atomic, Molecular and Optical Physics I |
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Chair: William Fairbank, Colorado State University Room: Science Building 280 |
Friday, October 17, 2014 1:50PM - 2:14PM |
D6.00001: Creating X-ray laser beams and ultra-high energy density matter on a table-top Jorge Rocca Intense soft x-ray laser beams and a new ultra-hot matter regime can both be created by irradiating materials with ultrafast pulses from compact optical lasers. Rapid transient heating creates highly ionized plasmas in which soft x-ray radiation is amplified into powerful laser beams. Advances in ultrafast solid state lasers now make it possible to create these plasmas at up to 100 Hz repetition rate, resulting in the table-top generation of high average power soft x-ray laser beams. These compact soft x-ray lasers can modify, analyze, and image matter with nano-scale resolution. We have also recently demonstrated that trapping of femtosecond optical laser pulses of relativistic intensity deep within ordered nanowire arrays can volumetrically heat dense matter into a new ultra-hot plasma regime. Near solid density arrays of metallic nanowires were heated to multi-keV temperatures using laser pulses of only 0.5 J energy. We obtained extraordinarily high degrees of ionization (eg. 52 times ionized Au), and gigabar pressures only exceeded in the central hot-spot of highly compressed thermonuclear fusion plasmas. These plasmas are efficient emitters of hard x-ray radiation. Scaling to higher laser intensities promises to create plasmas with temperatures and pressures approaching those in the center of the sun. Work supported by U.S Department of Energy, the National Science Foundation, and the Defense Threat Reduction Agency. [Preview Abstract] |
Friday, October 17, 2014 2:14PM - 2:26PM |
D6.00002: Fresnel-regime Coherent Diffractive Imaging using Tabletop Sources Matthew Tyson, Kimberly Nguyen, Jonathan Gigax, Richard Sandberg Coherent diffractive imaging (CDI) is a technique which aims to alleviate issues often associated with X-ray microscopy, such as inefficient light transmission, limited resolution, and lenses that are difficult to produce. CDI can be used in conjunction with an ultrafast pulsed X-ray source in order to achieve nanometer scale spatial and femtosecond scale temporal resolution. In order to resolve such fine details, CDI relies on oversampled diffraction patterns, which are then manipulated via a procedure known as iterative phase retrieval to reconstruct an image of the original sample. This technique typically requires the detector to be placed in the far-field regime in order to obtain a Fraunhofer diffraction pattern, where the wavefront can be assumed to be a plane wave. In near-field Fresnel diffraction, the wavefront on the detector has considerable phase-distortion, significantly complicating the reconstruction algorithm. The further into the Fresnel regime the detector is placed, the more substantial the phase-distortion. Here, we demonstrated Fresnel-regime CDI using a tabletop HeNe laser, analogous to a coherent X-ray source, and the effects of reconstructing a sample in the Fresnel regime were examined. [Preview Abstract] |
Friday, October 17, 2014 2:26PM - 2:38PM |
D6.00003: Single and Multi-Photon X-Ray Diffraction Dmitry Panin This project utilized the use of an X-ray detector apparatus to study the low-intensity crystal diffraction patterns for a range of wavelengths between 50 and 150 picometers. The purpose was to determine whether or not single photon diffraction is possible. The possible application of such technology can be employed in x-ray or nanometer scale photolithography techniques. The results have shown that a single photon can indeed interact with itself and therefore two or more sources are not needed for diffraction to occur and one source photon at a time is sufficient. [Preview Abstract] |
Friday, October 17, 2014 2:38PM - 2:50PM |
D6.00004: Search for Laser Second Harmonic Generation in Helium Chris Olsen, David Squires, Michael Ware, Justin Peatross Strong-field laser-atom interactions provide extreme conditions that may be useful for investigating the de Broglie-Bohm interpretation of quantum mechanics. Bohmian trajectories representing bound electrons in individual atoms exhibit both even and odd harmonic motion when subjected to a strong applied laser field. If even harmonics from symmetric atomic potentials such as helium are observed, it would suggest that the de Broglie/Bohm interpretation possesses a certain predictive power within the semiclassical framework, which aims for consistency with QED. The ramifications might impact how we view quantum wave functions and associated notions such as ``wave-function collapse.'' Even-order harmonics computed using Bohmian mechanics carry random phase, dependent on initial positions of trajectories within the wave function. Under the conjecture that a Bohmian point particle plays the role of light emitter, the random phase would explain why even harmonics generated in monatomic gasses have not been observed to date, since the emission would be incoherent. We report on a search for the possibility of faint even-harmonic incoherent emission from helium. [Preview Abstract] |
Friday, October 17, 2014 2:50PM - 3:02PM |
D6.00005: Superradiance in Non-Phasematched Laser Third Harmonic Emission from Helium David Squires, Justin Peatross, Michael Ware, Chris Olsen We report on single-photon measurements out the side of an intense laser, which is focused into a chamber filled with up to 10 atm of helium. Third-harmonic photons scattered by the 800-nm short laser pulses are readily observed. For a collection of atoms with randomized locations, and if the atoms act independently (classically), the emission into poorly phase-matched directions is the same whether the emission process is coherent or incoherent. The signal strength in that case would be proportional to the number of atoms exposed to the intense laser field. However, the third harmonic intensity is observed to be proportional to the square of the density, indicating cooperative effects between atoms in close proximity, this in spite of the fact that the atoms are only weakly excited with virtually no population remaining in any excited state after the laser pulse passes. In the experiment, over $10^5$ atoms are confined within a half wavelength of the harmonic. [Preview Abstract] |
Friday, October 17, 2014 3:02PM - 3:14PM |
D6.00006: Measurement of lateral radiation from free-electrons in an intense laser focus Matthew Ashby, James Fletcher, Justin Peatross, Michael Ware We report the result from an experimental measurement of light scattered by individual free electrons in an intense laser focus. This system becomes particularly interesting when the electron wavepacket spreads to the scale of an optical wavelength, as naturally happens during the ionization process of helium in a high-intensity laser focus. As the different parts of the wavepacket oscillate out of phase, the question naturally arises whether the different parts of the wave packet can interfere with each other in the radiative process. If this interference were possible, radiation from an electron wavepacket would be strongly suppressed as it gets larger. [Preview Abstract] |
Friday, October 17, 2014 3:14PM - 3:26PM |
D6.00007: Computational Modeling of the Radiation from Free Electrons in an Intense Laser Focus James Fletcher, Matt Ashby, Michael Ware We report the result of a simulation of the light scattered by individual free electrons in an intense laser focus.~ We treat the laser as a classical light field and electrons as point particles initially bound in an atom-like potential. Then we crudely simulate the ionization process of helium in an intense focus and calculate the radiation patterns and intensity from free electrons born in this process. The classical model provides a benchmark for comparing the radiation we observe in our experiment where we are able to see the effect of the electron wavepacket size on the emitted radiation. [Preview Abstract] |
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