Open Access. Powered by Scholars. Published by Universities.®
Articles 1 - 8 of 8
Full-Text Articles in Physics
Experimental Observation Of Relativistic Nonlinear Thomson Scattering, Szu-Yuan Chen, Anatoly Maksimchuk, Donald Umstadter
Experimental Observation Of Relativistic Nonlinear Thomson Scattering, Szu-Yuan Chen, Anatoly Maksimchuk, Donald Umstadter
Donald Umstadter Publications
Classical Thomson scattering—the scattering of low-intensity light by electrons—is a linear process, in that it does not change the frequency of the radiation; moreover, the magnetic-field component of light is not involved. But if the light intensity is extremely high (~1018 Wcm–2), the electrons oscillate during the scattering process with velocities approaching the speed of light. In this relativistic regime, the effect of the magnetic and electric fields on the electron motion should become comparable, and the effective electron mass will increase. Consequently, electrons in such high fields are predicted to quiver nonlinearly, moving in figure-eight patterns …
Relativistic Nonlinear Optics, Phillip F. Schewe, Ben Stein, Donald P. Umstadter
Relativistic Nonlinear Optics, Phillip F. Schewe, Ben Stein, Donald P. Umstadter
Donald Umstadter Publications
Laser light is a convenient way of transporting both electric and magnetic fields. When an electron encounters light, however, it is usually the electric field that does the talking; the magnetic part of light is less influential since its effect on the electron is proportional to the electron's speed as a fraction of the speed of light (c). In new experiments at the University of Michigan this is all changed since the intensity of the laser light used is so great (a terawatt of power, compared to a milliwatt for a laser in a CD player) that the electrons in …
Laser-Plasma Harmonics With High-Contrast Pulses And Designed Prepulses, R.S. Marjoribanks, L. Zhao, F.W. Budnik, G. Kulcsar, A. Vitcu, H. Higaki, R. Wagner, Anatoly Maksimchuk, Donald P. Umstadter, S.P. Le Blanc, M.C. Downer
Laser-Plasma Harmonics With High-Contrast Pulses And Designed Prepulses, R.S. Marjoribanks, L. Zhao, F.W. Budnik, G. Kulcsar, A. Vitcu, H. Higaki, R. Wagner, Anatoly Maksimchuk, Donald P. Umstadter, S.P. Le Blanc, M.C. Downer
Donald Umstadter Publications
One aspect of the complexity of mid- and high-harmonic generation in highintensity laser-plasma interactions is that nonlinear hydrodynamics is virtually always folded together with the nonlinear optical conversion process. We have partly dissected this issue in picosecond and subpicosecond interactions with preformed plasma gradients, imaging and spectrally resolving low- and mid-order harmonics. We describe spatial breakup of the picosecond beam in preformed plasmas, concomitant broaden~ng and breakup of the harmonic spectrum. presumably through self-phase modulation, together with data on the sensitivity of harmonics production efficiency to the gradient or extent of prefomed plasma. Lastly. we show preliminary data of regular …
Method And Apparatus For Generating And Accelerating Ultrashort Electron Pulses, Donald P. Umstadter, Joon-Koo Kim, Evan Dodd
Method And Apparatus For Generating And Accelerating Ultrashort Electron Pulses, Donald P. Umstadter, Joon-Koo Kim, Evan Dodd
Donald Umstadter Publications
The invention provides a novel laser-plasma-based source of relativistic electrons; and a method to use laser-driven plasma waves as the basis for the source of electrons. The technique involves a combination of laser beams, which are focused in a plasma. One beam creates a wakefield plasma wave and the other beam alters the trajectory of background electrons, such that they become trapped in the plasma wave and are then accelerated to relativistic velocities, preferably in a distance less than a millimeter. In another embodiment, the second beam removes electrons from atomic ions previously generated by the first beam thereby providing …
Cold Relativistic Wavebreaking, J.K. Kim, Donald P. Umstadter
Cold Relativistic Wavebreaking, J.K. Kim, Donald P. Umstadter
Donald Umstadter Publications
The two-dimensional wave-breaking of relativistic plasma waves driven by a ultrashort high-power lasers, is described within a framework of cold 2-D fluid theory. It is shown that the transverse nonlinearity of the plasma wave results in temporally increasing transverse plasma oscillation in the wake of the laser pulse, inevitably inducing wave-breaking below the 1-D threshold. A condition for wavebreaking is obtained and evaluated. A preformed density channel is found to partially cancel the effect and increase the length of wakefield that survives before wavebreaking occurs.
Pressure Ionization And Line Merging In Strongly Coupled Plasmas Produced By 100-Fs Laser Pulses, M. Nantel, G. Ma, S. Gu, C.Y. Côté, J. Itatani, Donald Umstadter
Pressure Ionization And Line Merging In Strongly Coupled Plasmas Produced By 100-Fs Laser Pulses, M. Nantel, G. Ma, S. Gu, C.Y. Côté, J. Itatani, Donald Umstadter
Donald Umstadter Publications
Time- and space-resolved extreme ultraviolet spectra of carbon plasmas, created with 100-fs laser pulses, are obtained with the novel technique of picosecond jitter-free streak-camera averaging. Spectroscopic diagnostics indicate electron densities and temperatures evolving from 1023 to 1021 cm-3 and 80 to 50 eV, respectively, implying less than one particle in a Debye sphere at early times. The emission reveals conditions of extreme pressure ionization and line merging. Comparisons of the experimental spectra with numerical simulations validate the use of the Inglis-Teller limit for line merging, and confirm that pressure ionization models based on the Debye-Huckel potential are …
Evolution Of A Plasma Waveguide Created During Relativistic-Ponderomotive Self-Channeling Of An Intense Laser Pulse, Shouyuan Chen, G.S. Sarkisov, Anatoly Maksimchuk, R. Wagner, Donald P. Umstadter
Evolution Of A Plasma Waveguide Created During Relativistic-Ponderomotive Self-Channeling Of An Intense Laser Pulse, Shouyuan Chen, G.S. Sarkisov, Anatoly Maksimchuk, R. Wagner, Donald P. Umstadter
Donald Umstadter Publications
An on-axis plasma density depression channel was observed during and after the passage of a relativistically and ponderomotively self-guided laser pulse through a plasma. Optical interferometry was used to produce time-resolved plasma density distributions, revealing the formation of a plasma waveguide. These results were complemented by the guiding of a collinear trailing pulse.
Temporal Contrast In Ti:Sapphire Lasers: Characterization And Control, Marc Nantel, Jiro Itatani, An-Chun Tien, Jerome Faure, Daniel Kaplan, Marcel Bouvier, Takashi Buma, Paul Van Rompay, John Nees, Peter P. Pronko, Donald P. Umstadter, Gerald A. Mourou
Temporal Contrast In Ti:Sapphire Lasers: Characterization And Control, Marc Nantel, Jiro Itatani, An-Chun Tien, Jerome Faure, Daniel Kaplan, Marcel Bouvier, Takashi Buma, Paul Van Rompay, John Nees, Peter P. Pronko, Donald P. Umstadter, Gerald A. Mourou
Donald Umstadter Publications
As ultrafast lasers achieve ever higher focused intensities on target, the problem of ensuring a clean laser-solid interaction becomes more pressing. In this paper, we give concrete examples of the deleterious effects of low-contrast interactions, and address the problem of subpicosecond laser intensity contrast ratio on both characterization and control fronts. We present the new technique of high-dynamic-range plasma-shuttered streak camera contrast measurement, as well as two efficient and relatively inexpensive ways of improving the contrast of short pulse lasers without sacrificing on the output energy: a double-pass Pockels cell (PC), and clean high-energy-pulse seeding of the regenerative amplifier.