Open Access. Powered by Scholars. Published by Universities.®
Articles 1 - 17 of 17
Full-Text Articles in Physics
Photonuclear Physics: Laser Splits Atom, Donald Umstadter
Photonuclear Physics: Laser Splits Atom, Donald Umstadter
Donald P. Umstadter
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 uranium …
High-Energy Ion Generation By Short Laser Pulses, A. Maksimchuk, K. Flippo, H. Krause, G. Mourou, K. Nemoto, D. Schultz, Donald Umstadter, R. Vane, V. Yu. Bychenkov, G.I. Dudnikova, V.F. Kovalev, K. Mima, V.N. Novikov, Y. Sentoku, S.V. Tolokonnikov
High-Energy Ion Generation By Short Laser Pulses, A. Maksimchuk, K. Flippo, H. Krause, G. Mourou, K. Nemoto, D. Schultz, Donald Umstadter, R. Vane, V. Yu. Bychenkov, G.I. Dudnikova, V.F. Kovalev, K. Mima, V.N. Novikov, Y. Sentoku, S.V. Tolokonnikov
Donald P. Umstadter
This paper reviews the many recent advances at the Center for Ultrafast Optical Science (CUOS) at the University of Michigan in multi-MeV ion beam generation from the interaction of short laser pulses focused onto thin foil targets at intensities ranging from 1017 to 1019 W/cm2. Ion beam characteristics were studied by changing the laser intensity, laser wavelength, target material, and by depositing a well-absorbed coating. We manipulated the proton beam divergence using shaped targets and observed nuclear transformation induced by high-energy protons and deuterons. Qualitative theoretical approaches and fully relativistic two-dimensional particle-in-cell simulations modeled energetic ion …
Criss-Crossing Laser Beams Zoom Electrons Along, P. Zhang, N. Saleh, S. Chen, Z.M. Sheng, Donald Umstadter
Criss-Crossing Laser Beams Zoom Electrons Along, P. Zhang, N. Saleh, S. Chen, Z.M. Sheng, Donald Umstadter
Donald P. Umstadter
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 …
Laser-Energy Transfer And Enhancement Of Plasma Waves And Electron Beams By Interfering High-Intensity Laser Pulses, P. Zhang, N. Saleh, S. Chen, Z.M. Sheng, Donald Umstadter
Laser-Energy Transfer And Enhancement Of Plasma Waves And Electron Beams By Interfering High-Intensity Laser Pulses, P. Zhang, N. Saleh, S. Chen, Z.M. Sheng, Donald Umstadter
Donald P. Umstadter
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 decreased electron-beam divergence angle (by 45%), as …
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, A. Maksimchuk, Donald 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, A. Maksimchuk, Donald Umstadter, S.P. Le Blanc, M.C. Downer
Donald P. Umstadter
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 …
Relativistic Laser–Plasma Interactions, Donald Umstadter
Relativistic Laser–Plasma Interactions, Donald Umstadter
Donald P. Umstadter
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 …
Nonlinear Plasma Waves Resonantly Driven By Optimized Laser Pulse Trains, Donald Umstadter, E. Esarey, J. Kim
Nonlinear Plasma Waves Resonantly Driven By Optimized Laser Pulse Trains, Donald Umstadter, E. Esarey, J. Kim
Donald P. Umstadter
A method for generating large-amplitude plasma waves, which utilizes an optimized train of independently adjustable, intense laser pulses, is discussed and analyzed. Both the pulse widths and interpulse spacings are optimally determined such that resonance is maintained and the plasma wave amplitude is maximized. By mitigating the effects of both phase and resonant detuning, and by reducing laser-plasma instabilities, the use of appropriately tailored multiple laser pulses is a highly advantageous technique for accelerating electrons. Practical methods of producing the required pulse trains are suggested.
Submillimeter-Resolution Radiography Of Shielded Structures With Laser-Accelerated Electron Beams, Viswanathan Ramanathan, Sudeep Banerjee, Nathan Powers, Nathaniel Cunningham, Nathan A. Chandler-Smith, Kun Zhao, Kevin Brown, Donald Umstadter, Shaun Clarke, Sara Pozzi, James Beene, Randy Vane, David Schultz
Submillimeter-Resolution Radiography Of Shielded Structures With Laser-Accelerated Electron Beams, Viswanathan Ramanathan, Sudeep Banerjee, Nathan Powers, Nathaniel Cunningham, Nathan A. Chandler-Smith, Kun Zhao, Kevin Brown, Donald Umstadter, Shaun Clarke, Sara Pozzi, James Beene, Randy Vane, David Schultz
Donald P. Umstadter
We investigate the use of energetic electron beams for high-resolution radiography of flaws embedded in thick solid objects. A bright, monoenergetic electron beam (with energy >100 MeV) was generated by the process of laser-wakefield acceleration through the interaction of 50-TW, 30-fs laser pulses with a supersonic helium jet. The high energy, low divergence, and small source size of these beams make them ideal for high-resolution radiographic studies of cracks or voids embedded in dense materials that are placed at a large distance from the source. We report radiographic imaging of steel with submillimeter resolution.
Competition Between Ponderomotive And Thermal Forces In Short-Scale-Length Laser Plasmas, X. Liu, Donald Umstadter
Competition Between Ponderomotive And Thermal Forces In Short-Scale-Length Laser Plasmas, X. Liu, Donald Umstadter
Donald P. Umstadter
Interactions of intense 400-fs laser pulses with a solid target are studied with time-integrated and time-resolved measurements. The latter are accomplished by means of a pump and probe experiment, in which the motion of the critical surface is measured with 250-fs resolution. It is found that when the average electron quiver energy (mvos2/2) becomes comparable to the electron thermal energy (kTe), the ponderomotive force of the high-intensity laser significantly reduces the thermal expansion of a laser plasma. This study is performed in an interesting regime not easily accessible with longer pulse lasers, in which the electron density scale length during …
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, V. Malka, S. Fritzler, Donald 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, V. Malka, S. Fritzler, Donald Umstadter, D. Hulin
Donald P. Umstadter
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.
Method For Generating A Plasma Wave To Accelerate Electrons, Donald Umstadter, Eric Esarey, Joon K. Kim
Method For Generating A Plasma Wave To Accelerate Electrons, Donald Umstadter, Eric Esarey, Joon K. Kim
Donald P. Umstadter
The invention provides a method and apparatus for generating large amplitude nonlinear plasma waves, driven by an optimized train of independently adjustable, intense laser pulses. In the method, optimal pulse widths, interpulse spacing, and intensity profiles of each pulse are determined for each pulse in a series of pulses. A resonant region of the plasma wave phase space is found where the plasma wave is driven most efficiently by the laser pulses. The accelerator system of the invention comprises several parts: the laser system, also called beam source, which preferably comprises photo cathode electron source and RF-LINAC accelerator; electron photo-cathode …
Development Of A Source Of Quasi-Monochromatic Mev Energy Photons, Donald Umstadter, Sudeep Banerjee, Viswanathan Ramanathan, Nathan Powers, Nathaniel Cunningham, Nathan A. Chandler-Smith
Development Of A Source Of Quasi-Monochromatic Mev Energy Photons, Donald Umstadter, Sudeep Banerjee, Viswanathan Ramanathan, Nathan Powers, Nathaniel Cunningham, Nathan A. Chandler-Smith
Donald P. Umstadter
We report current progress on a project to develop an all-optically-driven x-ray photon source. A laser pulse with 40-50 TW of peak power is focused on a supersonic helium nozzle to drive a relativistic plasma wave. Electron beams with energies of 320 MeV (+/- 28 MeV) are accelerated by means of laser wakefield acceleration. Remarkably, the acceleration region is only 3 mm in length. This accelerator is currently being employed to demonstrate the generation of MeV- energy x-ray by means of all-optical Thomson scattering. By this mechanism, a lower power, laser pulse (from the same laser system) is focused onto …
A Cone Of Coherent Light, S.-Y. Chen, A. Maksimchuk, E. Esarey, Donald Umstadter
A Cone Of Coherent Light, S.-Y. Chen, A. Maksimchuk, E. Esarey, Donald Umstadter
Donald P. Umstadter
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 …
Plasma Density Gratings Induced By Intersecting Laser Pulses In Underdense Plasmas, Z.-M. Sheng, J. Zhang, Donald Umstadter
Plasma Density Gratings Induced By Intersecting Laser Pulses In Underdense Plasmas, Z.-M. Sheng, J. Zhang, Donald Umstadter
Donald P. Umstadter
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 that of …
Observation Of Relativistic Cross-Phase Modulation In High-Intensity Laser-Plasma Interactions, Shouyuan Chen, Matthew Rever, P. Zhang, W. Theobald, Donald Umstadter
Observation Of Relativistic Cross-Phase Modulation In High-Intensity Laser-Plasma Interactions, Shouyuan Chen, Matthew Rever, P. Zhang, W. Theobald, Donald Umstadter
Donald P. Umstadter
A nonlinear optical phenomenon, relativistic cross-phase modulation, is reported. A relativistically intense light beam (I=1.3×1018 W cm-2, λ =1.05 μm) is experimentally observed to cause phase modulation of a lower intensity, copropagating light beam in a plasma. The latter beam is generated when the former undergoes the stimulated Raman forward scattering instability. The bandwidth of the Raman satellite is found to be broadened from 3.8–100 nm when the pump laser power is increased from 0.45–2.4 TW. A signature of relativistic cross-phase modulation, namely, asymmetric spectral broadening of the Raman signal, is observed at a pump power of 2.4 TW. The …
A Unidirectional, Pulsed Far-Infrared Ring Laser, W.A. Peebles, Donald Umstadter, D.L. Brower, N.C. Luhmann
A Unidirectional, Pulsed Far-Infrared Ring Laser, W.A. Peebles, Donald Umstadter, D.L. Brower, N.C. Luhmann
Donald P. Umstadter
The first study of a pulsed, far-infrared, ring laser is described. Unidirectional, traveling-wave operation is observed, thereby eliminating the spatial hole burning effects present in linear cavities. Single-mode output powers of 100 kW have been obtained.
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 P. Umstadter
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 rather than in …