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Full-Text Articles in Physics
Laser-Energy Transfer And Enhancement Of Plasma Waves And Electron Beams By Interfering High-Intensity Laser Pulses, P. Zhang, N. Saleh, Shouyuan Chen, Z.M. Sheng, Donald P. Umstadter
Laser-Energy Transfer And Enhancement Of Plasma Waves And Electron Beams By Interfering High-Intensity Laser Pulses, P. Zhang, N. Saleh, Shouyuan Chen, Z.M. Sheng, Donald P. Umstadter
Donald Umstadter Publications
The effects of interference due to crossed laser beams were studied experimentally in the high-intensity regime. Two ultrashort (400 fs), high-intensity (4×1017 and 1.6×1018 W/cm2) and1µm wavelength laser pulses were crossed in a plasma of density 4×1019 cm3. Energy was observed to be transferred from the higher-power to the lower-power pulse, increasing the amplitude of the plasma wave propagating in the direction of the latter. This results in increased electron self-trapping and plasma-wave acceleration gradient, which led to an increased number of hot electrons (by 300%) and hot-electron temperature (by 70%) and a …
Criss-Crossing Laser Beams Zoom Electrons Along, P. Zhang, N. Saleh, Shouyuan Chen, Z.M. Sheng, Donald P. Umstadter
Criss-Crossing Laser Beams Zoom Electrons Along, P. Zhang, N. Saleh, Shouyuan Chen, Z.M. Sheng, Donald P. Umstadter
Donald Umstadter Publications
Crossing two high-intensity laser beams in a plasma (a collection of charged particles) can have some interesting effects. In a recent experiment performed by researchers at the University of Michigan and the Institute of Physics in China, energy from a higher-power laser pulse was transferred to a lower-power laser pulse. The lower-power pulse had been accelerating electrons with its "wakefield" (like a wave accelerating a surfer). The extra energy to this lower-power pulse enhanced the electron acceleration and decreased the divergence of the electron beam. These features are desirable for proposed "laser particle accelerators" that would be powered by relatively …
Plasma Density Gratings Induced By Intersecting Laser Pulses In Underdense Plasmas, Z.-M. Sheng, Jiandi Zhang, Donald Umstadter
Plasma Density Gratings Induced By Intersecting Laser Pulses In Underdense Plasmas, Z.-M. Sheng, Jiandi Zhang, Donald Umstadter
Donald Umstadter Publications
Electron and ion density gratings induced by two intersecting ultrashort laser pulses at intensities of 1016 W/cm2 or lower are investigated. The ponderomotive force generated by the inhomogeneous intensity distribution in the intersecting region of the interfering pulses produces deep electron and ion density modulations at a wavelength less than a laser wavelength in vacuum. Dependence of the density modulation on the plasma densities, temperatures, and the ion mass, as well as the laser pulse parameters are studied analytically and by particle-in-cell simulations. It is found that the density peaks of such gratings can be a few times …
Relativistic Laser–Plasma Interactions, Donald Umstadter
Relativistic Laser–Plasma Interactions, Donald Umstadter
Donald Umstadter Publications
By focusing petawatt peak power laser light to intensities up to 1021 Wcm−2, highly relativistic plasmas can now be studied. The force exerted by light pulses with this extreme intensity has been used to accelerate beams of electrons and protons to energies of a million volts in distances of only microns. This acceleration gradient is a thousand times greater than in radio-frequency-based accelerators. Such novel compact laser-based radiation sources have been demonstrated to have parameters that are useful for research in medicine, physics and engineering. They might also someday be used to ignite controlled thermonuclear fusion. Ultrashort …
Backscattering Of An Intense Laser Beam By An Electron, Fei He, Y.Y. Lau, Donald P. Umstadter, Richard Kowalczyk
Backscattering Of An Intense Laser Beam By An Electron, Fei He, Y.Y. Lau, Donald P. Umstadter, Richard Kowalczyk
Donald Umstadter Publications
We present a novel, simple asymptotic expansion for the spectrum of radiation that is backscattered from a laser by a counterpropagating (or copropagating) electron. The solutions are presented in such a way that they explicitly show the relative merit of using an intense laser and of an energetic electron beam in x-ray production in the single particle regime. Simple scaling laws are given.
X-Ray Radiation From Nonlinear Thomson Scattering Of An Intense Femtosecond Laser On Relativistic Electrons In A Helium Plasma, K. Ta Phuoc, A. Rousse, M. Pittman, J.P. Rousseau, Victor Malka, S. Fritzler, Donald P. Umstadter, D. Hulin
X-Ray Radiation From Nonlinear Thomson Scattering Of An Intense Femtosecond Laser On Relativistic Electrons In A Helium Plasma, K. Ta Phuoc, A. Rousse, M. Pittman, J.P. Rousseau, Victor Malka, S. Fritzler, Donald P. Umstadter, D. Hulin
Donald Umstadter Publications
We have generated x-ray radiation from the nonlinear Thomson scattering of a 30 fs/1.5 J laser beam on plasma electrons. A collimated x-ray radiation with a broad continuous spectrum peaked at 0.15 keV with a significant tail up to 2 keV has been observed. These characteristics are found to depend strongly on the laser strength parameter a0. This radiative process is dominant for a0 greater than unity at which point the relativistic scattering of the laser light originates from MeV energy electrons inside the plasma.
An Optical Trap For Relativistic Plasma, Ping Zhang, Ned Saleh, Shouyuan Chen, Zhengming Sheng, Donald Umstadter
An Optical Trap For Relativistic Plasma, Ping Zhang, Ned Saleh, Shouyuan Chen, Zhengming Sheng, Donald Umstadter
Donald Umstadter Publications
The first optical trap capable of confining relativistic electrons, with kinetic energy <350 keV was created by the interference of spatially and temporally overlapping terawatt power, 400 fs duration laser pulses (<2.4x1018 W/cm2) in plasma. Analysis and computer simulation predicted that the plasma density was greatly modulated, reaching a peak density up to 10 times the background density (ne /n0;10) at the interference minima. Associated with this charge displacement, a direct-current electrostatic field of strength of ~2 x 1011 eV/m was excited. These predictions were confirmed experimentally by Thomson and Raman scattering diagnostics. Also confirmed were predictions that the electron density grating acted as a multi-layer mirror to transfer energy between the crossed laser beams, resulting …
Erratum: ‘‘Phase Dependence Of Thomson Scattering In An Ultraintense Laser Field’’ Phys. Plasmas 9, 4325 [2002], Fei He, Y. Y. Lau, Donald P. Umstadter, Trevor Strickler
Erratum: ‘‘Phase Dependence Of Thomson Scattering In An Ultraintense Laser Field’’ Phys. Plasmas 9, 4325 [2002], Fei He, Y. Y. Lau, Donald P. Umstadter, Trevor Strickler
Donald Umstadter Publications
The conclusions of this paper on the frequency scaling of the peak intensity of Thomson scattering of an electron that is initially at rest are restricted to the backscatter direction of the laser. All data were obtained only for the backscatter direction. In the forward direction of the laser, there is no frequency upshift. At an oblique angle that depends on the normalized laser field amplitude, ω/ω0 ~ O(a3) for large a, where ω0 is the laser frequency and a is the normalized laser electric field amplitude. Also, in Fig. 3, a = …