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Articles 61 - 64 of 64
Full-Text Articles in Physical Sciences and Mathematics
Relativistic Plasma-Wave Excitation By Collinear Optical Mixing, C.E. Clayton, C. Joshi, C. Darrow, Donald P. Umstadter
Relativistic Plasma-Wave Excitation By Collinear Optical Mixing, C.E. Clayton, C. Joshi, C. Darrow, Donald P. Umstadter
Donald P. Umstadter
The relativistic plasma wave excited when the frequency difference between two copropagating CO2 laser beams equals the plasma frequency is detected for the first time. The plasma-wave frequency, wave number, spatial extent, and saturation time are directly measured by use of 7-mrad, collective, ruby Thomson scattering and the forward-scattered ir spectrum. The wave amplitude ñ/n0 is inferred to be (1-3)% which gives a longitudinal electric field of 0.3 to 1 GV/m at a laser intensity of 1.7×1013 W/cm2, in reasonable agreement with theory.
High-Energy Ion Generation In Interaction Of Short Laser Pulse With High-Density Plasma, Y. Sentoku, V. Y. Bychenkov, K. Flippo, Anatoly Maksimchuk, K. Mima, G. Mourou, Z. M. Sheng, Donald Umstadter
High-Energy Ion Generation In Interaction Of Short Laser Pulse With High-Density Plasma, Y. Sentoku, V. Y. Bychenkov, K. Flippo, Anatoly Maksimchuk, K. Mima, G. Mourou, Z. M. Sheng, Donald Umstadter
Donald P. Umstadter
Multi-MeV ion production from the interaction of a short laser pulse with a high-density plasma, accompanied by an underdense preplasma, has been studied with a particle-in- cell simulation and good agreement is found with experiment. The mechanism primarily responsible for the acceleration of ions is identified. Comparison with experiments sheds light on the ion-energy dependence on laser intensity, preplasma scale length, and relative ion energies for a multi-species plasma. Two regimes of maximum ion-energy dependence on laser intensity, I, have been identified: subrelativistic, μ I ; and relativistic, μ √I. Simulations show that the energy of the accelerated ions versus …
High-Energy Laser-Accelerated Electron Beans For Long-Range Interrogation, Nathaniel Cunningham, Sudeep Banerjee, Viswanathan Ramanathan, Nathan D. Powers, Nathan A. Chandler-Smith, Randy Vane, David Schultz, Sara Pozzi, Shaun Clark, James Beene, Donald Umstadter
High-Energy Laser-Accelerated Electron Beans For Long-Range Interrogation, Nathaniel Cunningham, Sudeep Banerjee, Viswanathan Ramanathan, Nathan D. Powers, Nathan A. Chandler-Smith, Randy Vane, David Schultz, Sara Pozzi, Shaun Clark, James Beene, Donald Umstadter
Donald P. Umstadter
We are studying the use of 0.1 - 1.0 GeV laser-accelerated electron beams as active interrogation probes for long-standoff radiography or nuclear activation of concealed special nuclear material. Use of beams in this energy range is largely unexplored, but such beams could provide notable advantages over lower-energy beams and x-rays. High-energy laser-accelerated electrons exhibit large penetration range through air and solids, and low beam divergence for both direct beams and secondary Bremsstrahlung x-rays. We present laboratory measurements of radiography and activation using the high power Diocles laser system at the University of Nebraska, as well as MCNP and GEANT Monte …
Nonlinear Analysis Of Relativistic Harmonic Generation By Intenselasers In Plasmas, Eric Esarey, A. Ting, P. Sprangle, Donald Umstadter, X. Liu
Nonlinear Analysis Of Relativistic Harmonic Generation By Intenselasers In Plasmas, Eric Esarey, A. Ting, P. Sprangle, Donald Umstadter, X. Liu
Donald P. Umstadter
A linearly polarized, ultra-intense laser field induces transverse plasma currents which are highly relativistic and nonlinear, resulting in the generation of coherent harmonic radiation in the forward direction (i.e., copropagating with the incident laser field). A nonlinear cold fluid model, valid for ultrahigh intensities, is formulated and used to analyze relativistic harmonic generation. The plasma density response is included self-consistently and is shown to significantly reduce the current driving the harmonic radiation. Phase detuning severely limits the growth of the harmonic radiation. The effects of diffraction are considered in the mildly relativistic limit. No third-harmonic signal emerges from a uniform …