Research Index / High-Field Science
Faculty: Donald Umstadter - Anatoly Maksimchuk - Gιrard Mourou
Research Fellow: Sudeep Banerjee
Collaborators: K. Nemoto (CREPI, Japan) - V. Yu. Bychenkov (Osaka University, Japan) - V. Rozmus and K. I. Kapchuk (University of Alberta, Canada)
Graduate Students: Kirk Flippo - Ned Saleh - Rahul Shah - Ping Zhang - Tony Valenzuela - Scott Sepke - Vina Wong - Teh Lin - Katherine Korbiak
Compact solid-state lasers can currently produce pulses with intensities in excess of 1018 W/cm2, corresponding to an electric field that exceeds 1012 eV/cm. Since plasma electrons oscillate in such a high field at relativistic velocities, nonlinear optics involving free electrons may now be studied. This includes harmonic generation, self-focusing, gigabar laser pressure (with applications to research into a concept for thermonuclear fusion called the fast ignitor), and wake-field plasma waves (with applications to novel compact particle accelerators).
Laser-Driven Nuclear Transformations One near-term application of laser-accelerated ions is the production of isotopes for nuclear physics and medicine. As shown in the figure below, these well-collimated beams of ionized hydrogen (deuterium) can be "fused" with elements like boron to transform the latter into radioactive carbon. We observed the production of > 105 atoms of the positron-active isotope 11C from the reaction 10B(d,n)11C. Such isotopes are commonly ingested by cancer patients and made to seek out tumors while they are undergoing radioactive decay. The resulting emission of gamma rays (energetic x-rays) is used to precisely locate the tumor in a commonplace technique called positron emission tomography (PET). Up until now, a large device called a cyclotron was required to produce the radioactive isotopes for PET. But ions are accelerated by our high-power laser in a 10,000-times shorter distance than in a cyclotron, providing the possibility of a much more compact and inexpensive isotope source. The activation results also suggest that the deuterons were accelerated from the front surface of the target. The beam of protons that can easily be produced by laser acceleration could have an important impact in oncology for ion therapy. Experiments in collaboration with the medical school are underway to assess the potential of this technology. [Publications: Applied Physics Letters, vol. 78, no. 5, p. 595, Jan. 2001 and Physical Review Letters, vol. 84, no. 18, p. 4108, May 2000.]
Control of Laser Acceleration Laser accelerators have reached a level of maturity where methods of control over output parameters rather than proof-of-principle experiments are the key issue. As a step in that direction, a novel method for the control of stimulated Raman scattering and hot electron production in short-pulse laser-plasma interactions was studied. It relies on the use of a linear frequency chirp in non-bandwidth limited pulses. Theoretical calculations show that a 12% bandwidth will eliminate Raman forward scattering for a plasma density that is 1% of the critical density. The predicted changes to the growth rate are confirmed in two-dimensional particle-in-cell simulations. [Physics of Plasma, vol. 8, no. 8, pp. 3531-3534, Aug. 2001.]
Fast-ignitor Fusion We have examined the feasibility of light-ion triggered spark ignition for inertial confinement fusion (ICF). By studying the ion range in the hot and compressed core of ICF targets as a function of ion energy, we have shown that a short-pulse laser with energy in excess of 200 kJ and focused intensity of 1021 W/cm2 is required to produce an ignition. [Plasma Physics Reports, 27, pp. 1017-1020, 2001.]
Phase-matched Harmonic Generation in an Ionized Gas We have successfully measured for the first time the coherent relativistic Thomson scattering of an intense laser from previously stationary electrons in plasma. The results have been published in Physical Review Letters [Physics Review Letters, vol. 84, no. 24, June 2000].
Electron Acceleration in Relativistic Plasma Waves New intriguing results on electron acceleration in a self-modulated laser wakefield have been obtained. Test-particle simulations have been performed to explain the experimental observations. The results have been published in Physics of Plasmas. [Physics of Plasmas, 6, p. 4739, 1999.]
High-energy Electron Spectrometer In collaboration with Drs. C. Keppel, W. Buck and P. Gueye from Hampton University we have built a high-energy electron spectrometer, which will be used for joint experiments in high-field science. Click here to see a photo of its construction.
Electron Acceleration from Laser Filamentation Electrons were accelerated for the first time in the interaction of an ultrashort (30 fs) laser pulse with plasma in the resonant regime, in which the laser pulse duration is approximately equal to the plasma period. The acceleration only occurred when the laser broke into filaments, but no evidence for Raman scattering was observed, indicating that the acceleration mechanism differed from previous experiments. [Physics Review Letters, vol. 84, no. 23, June 2000.]
Pulse Radiolysis of Liquid Water Using Picosecond Electron Pulses - In collaboration with researchers from Argonne National Laboratory, we have demonstrated that the picosecond electron bunches produced from a table-top laser were suitable for pulsed radiolysis experiments of liquid water. These types of experiments had only been performed previously with large radio-frequency accelerators. [Review of Scientific Instruments, vol. 71, no. 6, pp. 2305-2308, June 2000.]
Photoelectron Spectroscopy of Non-Sequential Double Ionization of Argon Multi-photon ionization has been modeled in many ways that approximate the atom-light system as a single active electron moving in some sort of ion, atom, or laser potential. These theoretically derived electron energy spectra do not consider events involving more than one electron, such as direct double-ionization; nonetheless, they closely match experimental above-threshold ionization (ATI) electron spectra, even though these must include electrons from all ionization processes that are present, including those involving correlation between two or more electrons. By recording coincidences between double ions and electrons, we filter the ATI electron spectrum to observe non-sequential double ionization (NSDI), a two-electron process outside the single active electron approximation. We observe a spike of zero-energy electrons, which is not predicted by the most basic rescattering approach, but could be a part of a revised rescattering model. Click here for more detailed information.
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