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Full-Text Articles in Physics
Saturation Of Beat-Excited Plasma Waves By Electrostatic Mode Coupling, C. Darrow, Donald P. Umstadter, T. Katsouleas, W.B. Mori, C.E. Clayton, C. Joshi
Saturation Of Beat-Excited Plasma Waves By Electrostatic Mode Coupling, C. Darrow, Donald P. Umstadter, T. Katsouleas, W.B. Mori, C.E. Clayton, C. Joshi
Donald P. Umstadter
The nature of plasma waves which are resonantly excited when two laser beams beat in a rippled-density plasma is explored both theoretically and experimentally. A theoretical model is presented which, for commonly encountered experimental parameters, predicts rapid saturation of the high—phase-velocity beat wave at an amplitude below that expected for relativistic detuning. Results of experimental studies of this process are presented.
Study Of Energetic Ion Generation From High-Intensity-Laser Dense-Plasma Interactions, K. Flippo, Anatoly Maksimchuk, Sudeep Banerjee, K. Nash, V. Wong, T. Lin, K. Nemoto, V. Yu. Bychenkov, Y. Sentoku, G. Mourou, Donald P. Umstadter
Study Of Energetic Ion Generation From High-Intensity-Laser Dense-Plasma Interactions, K. Flippo, Anatoly Maksimchuk, Sudeep Banerjee, K. Nash, V. Wong, T. Lin, K. Nemoto, V. Yu. Bychenkov, Y. Sentoku, G. Mourou, Donald P. Umstadter
Donald P. Umstadter
We report on the characteristics of an ultrafast-laser driven proton beam from thinfilm targets. The difference in proton beam profiles, beam energies, and laser induced back ablation plumes between a dielectric (Mylar) and a conductor (aluminum) are discussed. Evidence for front-side acceleration and a method for beam manipulation are also presented.
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 …
Laser Light In, 50-Mev Protons Out, Phillip F. Schewe, Ben Stein, Donald P. Umstadter
Laser Light In, 50-Mev Protons Out, Phillip F. Schewe, Ben Stein, Donald P. Umstadter
Donald P. Umstadter
At next week's meeting of the American Physical Society Division of Plasma Physics in Seattle, three groups will independently announce their ability to generate powerful, intense streams of ions by shining ultrashort laser pulses on tiny spots of solid material. Potentially, this approach offers an alternative to bulky, expensive ion accelerators for producing high-velocity ions useful for cancer therapy and electronics manufacturing. Using a single pulse of light from Livermore's Petawatt laser, the most powerful in the world, researchers at that laboratory (Scott Wilks, 925-422-2974, wilks@icf.llnl.gov) have reported generating 30 trillion protons with energies up to 50 MeV, from a …
Production Of A Kev X-Ray Beam From Synchrotron Radiation In Relativistic Laser-Plasma Interaction, Antoine Rousse, Kim Ta Phuoc, Rahul Shah, Alexander Pukhov, Eric Lefebvre, Victor Malka, Sergey Kiselev, Frederic Burgy, Jean-Philippe Rousseau, Donald P. Umstadter, Daniele Hulin
Production Of A Kev X-Ray Beam From Synchrotron Radiation In Relativistic Laser-Plasma Interaction, Antoine Rousse, Kim Ta Phuoc, Rahul Shah, Alexander Pukhov, Eric Lefebvre, Victor Malka, Sergey Kiselev, Frederic Burgy, Jean-Philippe Rousseau, Donald P. Umstadter, Daniele Hulin
Donald P. Umstadter
We demonstrate that a beam of x-ray radiation can be generated by simply focusing a single high-intensity laser pulse into a gas jet. A millimeter-scale laser-produced plasma creates, accelerates, and wiggles an ultrashort and relativistic electron bunch. As they propagate in the ion channel produced in the wake of the laser pulse, the accelerated electrons undergo betatron oscillations, generating a femtosecond pulse of synchrotron radiation, which has keV energy and lies within a narrow (50 mrad) cone angle.
An All Optical Laser Wakefield Electron Injector, Donald Umstadter
An All Optical Laser Wakefield Electron Injector, Donald Umstadter
Donald P. Umstadter
The personnel who were supported by the grant included the P.I. (Prof. Umstadter), several research scientists (A. Maksimchuk and V. Yanovsky), a postdoc (P. Zhang) and several graduate and undergraduate students. Although there were several setbacks in developing the novel laser technology required to produce a monoenergetic beam of electrons from an all-optical accelerator, several important steps were taken towards reaching that ultimate goal. The most important outcome of this project was that we demonstrated the principle of optical control of laser accelerators, namely, that one laser pulse could modify the properties (e.g., emittance and electron number) of an electron …
Temporal Characterization Of A Self-Modulated Laser Wakefield, S.P. Le Blanc, M.C. Downer, R. Wagner, Shouyuan Chen, Anatoly Maksimchuk, G. Mourou, Donald P. Umstadter
Temporal Characterization Of A Self-Modulated Laser Wakefield, S.P. Le Blanc, M.C. Downer, R. Wagner, Shouyuan Chen, Anatoly Maksimchuk, G. Mourou, Donald P. Umstadter
Donald P. Umstadter
The temporal envelope of plasma density oscillations in the wake of an intense (l∼4×1018 W/cm2, λ = 1 μm) laser pulse (400 fs) is measured using forward Thomson scattering from a copropagating, frequency-doubled probe pulse. The wakefield oscillations in a fully ionized helium plasma (ne = 3×1019 cm-3) are observed to reach maximum amplitude ( δne/ne∼0.1) 300 fs after the pump pulse. The wakefield growth ( 3.5 ps-1) and decay ( 1.9 ps-1) rates are consistent with the forward Raman scattering instability and Landau damping, respectively.
Signal Averaging X-Ray Streak Camera With Picosecond Jitter, Anatoly Maksimchuk, M. Kim, J. Workman, G. Korn, J. Squier, D. Du, Donald Umstadter, G. Mourou, M. Bouvier
Signal Averaging X-Ray Streak Camera With Picosecond Jitter, Anatoly Maksimchuk, M. Kim, J. Workman, G. Korn, J. Squier, D. Du, Donald Umstadter, G. Mourou, M. Bouvier
Donald P. Umstadter
We have developed an averaging picosecond x-ray streak camera using a dc-biased photoconductive switch as a generator of a high-voltage ramp. The streak camera is operated at a sweep speed of up to 8 ps/mm, shot-to-shot jitter is less than ±1 ps. The streak camera has been used to measure the time history of broadband x-ray emission from an ultrashort pulse laser-produced plasma. Accumulation of the streaked x-ray signals significantly improved the signal-to-noise ratio of the data obtained.
Electron Acceleration By A Laser Wakefield In A Relativistically Self-Guided Channel, R. Wagner, Shouyuan Chen, Anatoly Maksimchuk, Donald P. Umstadter
Electron Acceleration By A Laser Wakefield In A Relativistically Self-Guided Channel, R. Wagner, Shouyuan Chen, Anatoly Maksimchuk, Donald P. Umstadter
Donald P. Umstadter
Acceleration of electrons to relativistic energies by a multidimensional self-modulated laser wakefield is discussed. Above a power threshold, a relativistically self-guided channel from an intense ultrashort laser pulse (l∼4×1018 W/cm2, λ = 1 μm, τ = 400 fs) was found to increase the laser propagation distance, decrease the electron beam divergence, and increase the energy of the electrons. These electron beam effects occurred even though the propagation distance became significantly longer than the conventional dephasing length.
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 P. Umstadter
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 inapplicable in such …
“Atomic Processes In High Energy Density Plasmas," Summaries Of Fy 1997 Research In The Chemical Sciences, Donald P. Umstadter
“Atomic Processes In High Energy Density Plasmas," Summaries Of Fy 1997 Research In The Chemical Sciences, Donald P. Umstadter
Donald P. Umstadter
Several important plasma atomic processes are studied in a controlled manner. These studies are enabled by the recent invention of ultrashortpulse- duration lasers, which produce plasmas with independently controllable parameters.
Generation Of Tunable, 100–800 Mev Quasi-Monoenergetic Electron Beams From A Laser-Wakefield Accelerator In The Blowout Regime, Sudeep Banerjee, Nathan D. Powers, Viswanathan Ramanathan, I. Ghebregziabher, K. J. Brown, C. Maharjan, Shouyuan Chen, A. Beck, E. Lefebvre, Serguei Y. Kalmykov, Bradley Allan Shadwick, Donald Umstadter
Generation Of Tunable, 100–800 Mev Quasi-Monoenergetic Electron Beams From A Laser-Wakefield Accelerator In The Blowout Regime, Sudeep Banerjee, Nathan D. Powers, Viswanathan Ramanathan, I. Ghebregziabher, K. J. Brown, C. Maharjan, Shouyuan Chen, A. Beck, E. Lefebvre, Serguei Y. Kalmykov, Bradley Allan Shadwick, Donald Umstadter
Donald P. Umstadter
In this paper, we present results on a scalable high-energy electron source based on laser wakefield acceleration. The electron accelerator using 30–80 TW, 30 fs laser pulses, operates in the blowout regime, and produces high-quality, quasi-monoenergetic electron beams in the range 100–800 MeV. These beams have angular divergence of 1–4 mrad, and 5%–25% energy spread, with a resulting brightness 1011 electrons mm-2 MeV-1 mrad-2. The beam parameters can be tuned by varying the laser and plasma conditions. The use of a high-quality laser pulse and appropriate target conditions enables optimization of beam quality, concentrating a significant fraction of the accelerated …
Background-Free, Quasi-Monoenergetic Electron Beams From A Self-Injected Laser Wakefield Accelerator, Sudeep Banerjee, Serguei Y. Kalmykov, Nathan D. Powers, Viswanathan Ramanathan, Nathan A. Chandler-Smith, K. Brown, Shuo Chen, A. Moorthi, I. Ghebregziabher, C. Maharjan, Bradley Allan Shadwick, Donald Umstadter, A. Beck, E. Lefebvre, A. Cowan, D. Bruhwiler
Background-Free, Quasi-Monoenergetic Electron Beams From A Self-Injected Laser Wakefield Accelerator, Sudeep Banerjee, Serguei Y. Kalmykov, Nathan D. Powers, Viswanathan Ramanathan, Nathan A. Chandler-Smith, K. Brown, Shuo Chen, A. Moorthi, I. Ghebregziabher, C. Maharjan, Bradley Allan Shadwick, Donald Umstadter, A. Beck, E. Lefebvre, A. Cowan, D. Bruhwiler
Donald P. Umstadter
Stable 200–400-MeV quasi-monoenergetic electron bunches (ΔE/Eno dark-currentare produced when a self-injected laser plasma accelerator is optimized. PIC simulations demonstrate these beams are produced near the threshold for selfinjection.
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 P. Umstadter
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.
Study Of Laser Plasma Interactions In The Relativistic Regime, Donald Umstadter
Study Of Laser Plasma Interactions In The Relativistic Regime, Donald Umstadter
Donald P. Umstadter
We discuss the first experimental demonstration of electron acceleration by a laser wakefield over distances greater than a Rayleigh range (or the distance a laser normally propagates in vacuum). A self-modulated laser wakefield plasma wave is shown to have a field gradient that exceeds that of an RF Iinac by four orders of magnitude (E ≥ 200 GV/m) and accelerates electrons with over l-nC of charge per bunch in a beam with space-charge-limited emittance (1 mm-mrad). Above a laser power threshold, a plasma channel, created by the intense ultrashort laser pulse (I~ 4 x 1018 W/cm2, λ = 1 μm, …
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 …
Excitation And Damping Of A Self-Modulated Laser Wakefield, Shouyuan Chen, M. Krishnan, Anatoly Maksimchuk, Donald P. Umstadter
Excitation And Damping Of A Self-Modulated Laser Wakefield, Shouyuan Chen, M. Krishnan, Anatoly Maksimchuk, Donald P. Umstadter
Donald P. Umstadter
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.
Developments In Relativistic Nonlinear Optics, Donald P. Umstadter, Sudeep Banerjee, Shouyuan Chen, E. Dodd, K. Flippo, Anatoly Maksimchuk, N. Saleh, A. Valenzuela, P. Zhang
Developments In Relativistic Nonlinear Optics, Donald P. Umstadter, Sudeep Banerjee, Shouyuan Chen, E. Dodd, K. Flippo, Anatoly Maksimchuk, N. Saleh, A. Valenzuela, P. Zhang
Donald P. Umstadter
We report recent results of experiments and simulations in the regime of peak laser intensities above 1019 W/cm2, including the following topics: (1) electron and proton acceleration to energies in excess of 10 MeV in well collimated beams; (2) use of laser chirp to control the growth of plasma waves and acceleration of electrons by the Raman instability; (3) all optical injection and acceleration of electrons; (4) relativistic self-focusing by means of the mutual index of refraction of two overlapping laser pulses; (5) creation of a radioisotope by the reaction 10B(d,n)11C; (6) high-order harmonic generation from relativistic free electrons in …
Resonantly Laser-Driven Plasma Waves For Electron Acceleration, Donald P. Umstadter, J. Kim, Eric Esarey, E. Dodd, T. Neubert
Resonantly Laser-Driven Plasma Waves For Electron Acceleration, Donald P. Umstadter, J. Kim, Eric Esarey, E. Dodd, T. Neubert
Donald P. Umstadter
A method for generating large-amplitude nonlinear plasma waves, which utilizes an optimized train of independently adjustable, intense laser pulses, is analyzed in one dimension both theoretically and numerically (using both Maxwell-fluid and particle-in-cell codes). Optimal pulse widths and interpulse spacings are computed for pulses with either square or finite-rise-time sine shapes. A resonant region of the plasma wave phase space is found where the plasma wave is driven most efficiently by the laser pulses. The width of this region, and thus the optimal finite-rise-time laser pulse width, was found to decrease with increasing background plasma density and plasma wave amplitude, …
Observation Of Phase-Matched Relativistic Harmonic Generation, Shouyuan Chen, Anatoly Maksimchuk, Eric Esarey, Donald P. Umstadter
Observation Of Phase-Matched Relativistic Harmonic Generation, Shouyuan Chen, Anatoly Maksimchuk, Eric Esarey, Donald P. Umstadter
Donald P. Umstadter
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.
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 …
Tabletop Laser Accelerators Are On The Way, Phillip F. Schewe, Ben Stein, Donald P. Umstadter
Tabletop Laser Accelerators Are On The Way, Phillip F. Schewe, Ben Stein, Donald P. Umstadter
Donald P. Umstadter
The goal here is to use high electric fields in plasmas to accelerate electrons to 100-GeV energies over distances of meters rather than kilometers. This should promote the development of new particle colliders and x-ray sources. The predicted high acceleration gradients in plasmas have been achieved in recent years, but could only be used with external electron injection from a conventional source. Now scientists at the University of Michigan (Donald Umstadter, 313-764-2284) have made progress in eliminating conventional electron sources altogether. In a preliminary experiment, by simply focusing a laser into a plasma, the Michigan scientists have extracted a collimated …
Laser-Wakefield Accelerators: Glass-Guiding Benefits, Donald P. Umstadter
Laser-Wakefield Accelerators: Glass-Guiding Benefits, Donald P. Umstadter
Donald P. Umstadter
A main attraction of laser-driven electron accelerators is their absence of cavity walls, which can break down in the presence of intense electric fields. Now it seems that the inclusion of a hollow glass fibre cavity could lead to more efficient acceleration at lower laser intensities. ... Further research will reveal which of the above methods for guiding light will ultimately prove best for future accelerator designs. In any case, although it is perhaps ironic that the relatively old technology of glass waveguides may benefit next-generation accelerators, it is nonetheless satisfying to see such a classic photonic solution come to …
Simulation Of Ultrashort Electron Pulse Generation From Optical Injection Into Wake-Field Plasma Waves, D.S. Dodd, J.K. Kim, Donald P. Umstadter
Simulation Of Ultrashort Electron Pulse Generation From Optical Injection Into Wake-Field Plasma Waves, D.S. Dodd, J.K. Kim, Donald P. Umstadter
Donald P. Umstadter
A laser-plasma-based source of relativistic electrons is described in detail, and analyzed in two dimensions using theoretical and numeric techniques. Two laser beams are focused in a plasma, one exciting a wake-field electron plasma wave while another locally alters some electron trajectories in such a way that they can be trapped and accelerated by the wave. Previous analyses dealt only with one-dimensional models. In this paper two-dimensional particle-in-cell simulations and analysis of single particle trajectories show that the radial wake field plays an important role. The simulation results are interpreted to evaluate the accelerated electron beam's properties and compared with …
Method And Apparatus For Generating Laser Plasma X-Rays, Donald P. Umstadter, Jonathan Workman, Anatoly Maksimchuk, Xinbing Liu
Method And Apparatus For Generating Laser Plasma X-Rays, Donald P. Umstadter, Jonathan Workman, Anatoly Maksimchuk, Xinbing Liu
Donald P. Umstadter
The present information provides a system and an apparatus to produce x-rays from plasmas by focusing an intense, short duration optical pulse from a laser onto a target. The concentrated energy contained in the focused laser beam ionizes the target material, raising it to a temperature at which ions are produced in a chain reaction ionization, and x-rays are emitted when ions become de-excited (their electrons change energy level) or free electrons recombine with the ions in the plasma. The method comprises controlling pulse time duration of x-rays emitted from a plasma-forming target generating a beam of one or more …
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 P. Umstadter
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 …
Harmonic Generation By An Intense Laser Pulse In Neutral And Ionized Gases, X. Liu, Donald Umstadter, Eric Esarey, A. Ting
Harmonic Generation By An Intense Laser Pulse In Neutral And Ionized Gases, X. Liu, Donald Umstadter, Eric Esarey, A. Ting
Donald P. Umstadter
Reported are the results of a harmonic generation experiment in a simple gas (hydrogen) using 1-ps, 1-pm laser pulses with a range of intensities extending from below to far above the laser ionization saturation threshold. The scaling with intensity above saturation of the third harmonic generated by a single laser-pulse in a filled gas cell is observed to not fit with a simple model that takes into consideration volume ionization effects alone. In another experiment, a pump-probe type, an upper limit on the conversion efficiency of third harmonic generation in a preformed plasma is determined. It is found to be …
Detailed Dynamics Of Electron Beams Self-Trapped And Accelerated In A Self-Modulated Laser Wakefield, Shouyuan Chen, M. Krishnan, Anatoly Maksimchuk, R. Wagner, Donald P. Umstadter
Detailed Dynamics Of Electron Beams Self-Trapped And Accelerated In A Self-Modulated Laser Wakefield, Shouyuan Chen, M. Krishnan, Anatoly Maksimchuk, R. Wagner, Donald P. Umstadter
Donald P. Umstadter
The electron beam generated in a self-modulated laser-wakefield accelerator is characterized in detail. A transverse normalized emittance of 0.06 π mm mrad, the lowest ever for an electron injector, was measured for 2 MeV electrons. The electron beam was observed to have a multicomponent beam profile and energy distribution. The latter also undergoes discrete transitions as the laser power or plasma density is varied. In addition, dark spots that form regular modes were observed in the electron beam profile. These features are explained by analysis and test particle simulations of electron dynamics during acceleration in a three-dimensional plasma wakefield.
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 …