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University of Nebraska - Lincoln

2000

Donald Umstadter Publications

Articles 1 - 9 of 9

Full-Text Articles in Physics

Photonuclear Physics: Laser Splits Atom, Donald Umstadter Nov 2000

Photonuclear Physics: Laser Splits Atom, Donald Umstadter

Donald Umstadter Publications

Lasers have become ubiquitous, being used in everything from a bar-code reader to a compact disk player. Who would have thought that they might be used to split the atom? A few scientists proposed to do just that more that a decade ago. But accomplishing it in the laboratory had to await the maturity of new technology, which enabled the construction of the world's most powerful lasers at the Lawrence Livermore National Laboratory in the United States and at the Rutherford Appleton Laboratory in the United Kingdom. Now two independent research teams have used these lasers to split the ...


Tabletop Accelerators Are Brighter And Faster, Phil Schewe, Ben Stein, Donald P. Umstadter Nov 2000

Tabletop Accelerators Are Brighter And Faster, Phil Schewe, Ben Stein, Donald P. Umstadter

Donald Umstadter Publications

At last week's APS plasma physics meeting, Donald Umstadter of the University of Michigan's Center for Ultrafast Optical Science (734-764-2284, dpu@umich.edu) reported on advances at his lab and elsewhere in tabletop laser accelerators, devices that use light to accelerate beams of electrons and protons to energies of a million volts in distances of only microns. This acceleration rate or "gradient" is up to a thousand times larger than in conventional accelerators because the tabletop laser light can now exert pressures of gigabars, the highest ever achieved, and approaching the pressure of light near the Sun. Not ...


Observation Of Phase-Matched Relativistic Harmonic Generation, Shouyuan Chen, Anatoly Maksimchuk, Eric Esarey, Donald P. Umstadter Jun 2000

Observation Of Phase-Matched Relativistic Harmonic Generation, Shouyuan Chen, Anatoly Maksimchuk, Eric Esarey, Donald P. Umstadter

Donald Umstadter Publications

Phase-matched relativistic harmonic generation in plasmas is observed for the first time. Third-harmonic light is detected and discriminated spectrally and angularly from the harmonics generated from competing processes. Its angular pattern is a narrow forward-directed cone, which is consistent with phase matching of a high-order transverse mode in a plasma. The signal level is found to be on the same order of magnitude for a circularly polarized pump pulse as for a linearly polarized pump pulse.


Electron Acceleration And The Propagation Of Ultrashort High-Intensity Laser Pulses In Plasmas, Xiaofang Wang, Mohan Krishnan, Ned Saleh, Haiwen Wang, Donald P. Umstadter Jun 2000

Electron Acceleration And The Propagation Of Ultrashort High-Intensity Laser Pulses In Plasmas, Xiaofang Wang, Mohan Krishnan, Ned Saleh, Haiwen Wang, Donald P. Umstadter

Donald Umstadter Publications

Reported are interactions of high-intensity laser pulses ( λ = 810 nm and l≤3×1018 W/cm2) with plasmas in a new parameter regime, in which the pulse duration ( τ = 29 fs) corresponds to 0.6–2.6 plasma periods. Relativistic filamentation is observed to cause laser-beam breakup and scattering of the beam out of the vacuum propagation angle. A beam of megaelectronvolt electrons with divergence angle as small as 1° is generated in the forward direction, which is correlated to the growth of the relativistic filamentation. Raman scattering, however, is found to be much less than previous long-pulse ...


A Cone Of Coherent Light, Shouyuan Chen, Anatoly Maksimchuk, Eric Esarey, Donald P. Umstadter Jun 2000

A Cone Of Coherent Light, Shouyuan Chen, Anatoly Maksimchuk, Eric Esarey, Donald P. Umstadter

Donald Umstadter Publications

Lasers come in infrared and visible varieties, but none yet in the x-ray band. A compact and powerful source of coherent x rays is the dream of many physicists, who see applications such as making atomic scale, three-dimensional movies of a melting crystal or an operating photosynthesis protein. In a step toward that goal, a research team has detected high frequency coherent light generated by a new process. As they report in the 12 June PRL, intense laser pulses can stimulate free electrons in a plasma to emit coherent light at triple the input frequency in a narrowly-directed cone. The ...


Pulse Radiolysis Of Liquid Water Using Picosecond Electron Pulses Produced By A Table-Top Terawatt Laser System, Ned Saleh, Kirk Flippo, Koshichi Nemoto, Donald P. Umstadter, Robert A. Crowell, Charles D. Jonah, Alexander D. Trifunac Jun 2000

Pulse Radiolysis Of Liquid Water Using Picosecond Electron Pulses Produced By A Table-Top Terawatt Laser System, Ned Saleh, Kirk Flippo, Koshichi Nemoto, Donald P. Umstadter, Robert A. Crowell, Charles D. Jonah, Alexander D. Trifunac

Donald Umstadter Publications

A laser based electron generator is shown, for the first time, to produce sufficient charge to conduct time resolved investigations of radiation induced chemical events. Electron pulses generated by focussing terawatt laser pulses into a supersonic helium gas jet are used to ionize liquid water. The decay of the hydrated electrons produced by the ionizing electron pulses is monitored with 0.3 µs time resolution. Hydrated electron concentrations as high as 22 µM were generated. The results show that terawatt lasers offer both an alternative to linear accelerators and a means to achieve subpicosecond time resolution for pulse radiolysis studies.


Forward Ion Acceleration In Thin Films Driven By A High-Intensity Laser, Anatoly Maksimchuk, S. Gu, K. Flippo, Donald P. Umstadter, V. Yu. Bychenkov May 2000

Forward Ion Acceleration In Thin Films Driven By A High-Intensity Laser, Anatoly Maksimchuk, S. Gu, K. Flippo, Donald P. Umstadter, V. Yu. Bychenkov

Donald Umstadter Publications

A collimated beam of fast protons, with energies as high as 1.5 MeV and total number of ≳109, confined in a cone angle of 40°±10° is observed when a high-intensity high-contrast subpicosecond laser pulse is focused onto a thin foil target. The protons, which appear to originate from impurities on the front side of the target, are accelerated over a region extending into the target and exit out the back side in a direction normal to the target surface. Acceleration field gradients ∼10 GeV/cm are inferred. The maximum proton energy can be explained by the charge-separation ...


Dense And Relativistic Plasmas Produced By Compact High-Intensity Lasers, Donald Umstadter, Shouyuan Chen, G. Ma, Anatoly Maksimchuk, G. Mourou, M. Nantel, S. Pikuz, G. Sarkisov, R. Wagner Apr 2000

Dense And Relativistic Plasmas Produced By Compact High-Intensity Lasers, Donald Umstadter, Shouyuan Chen, G. Ma, Anatoly Maksimchuk, G. Mourou, M. Nantel, S. Pikuz, G. Sarkisov, R. Wagner

Donald Umstadter Publications

High-intensity lasers interacting with plasmas are used to study processes in the laboratory that would otherwise only occur in astrophysics. These include relativistic plasmas, electron acceleration in ultrahigh Ðeld-gradient wake Ðelds, pressure ionization and continuum lowering in strongly coupled plasmas, and X-ray line emission via Raman scattering.


Excitation And Damping Of A Self-Modulated Laser Wakefield, Shouyuan Chen, M. Krishnan, Anatoly Maksimchuk, Donald P. Umstadter Jan 2000

Excitation And Damping Of A Self-Modulated Laser Wakefield, Shouyuan Chen, M. Krishnan, Anatoly Maksimchuk, Donald P. Umstadter

Donald Umstadter Publications

Spatially, temporally, and angularly resolved collinear collective Thomson scattering was used to diagnose the excitation and damping of a relativistic-phase-velocity self-modulated laser wakefield. The excitation of the electron plasma wave was observed to be driven by Raman-type instabilities. The damping is believed to originate from both electron beam loading and modulational instability. The collective Thomson scattering of a probe pulse from the ion acoustic waves, resulting from modulational instability, allows us to measure the temporal evolution of the plasma temperature. The latter was found to be consistent with the damping of the electron plasma wave.