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Interaction of High Intensity Electromagnetic Waves with Plasmas

Description: The focus of our work during the duration of this grant was on the following areas: (a) the fundamental plasma physics of intense laser-plasma interactions, including the nonlinear excitation of plasma waves for accelerator applications, as well as the recently discovered by us phenomenon of the relativistic bi-stability of relativistic plasma waves driven by a laser beatwave; (b) interaction of high power microwave beams with magnetized plasma, including some of the recently discovered by us phenomena such as the Undulator Induced Transparency (UIT) as well as the new approaches to dynamic manipulation of microwave pulses; (c) investigations of the multi-color laser pulse interactions in the plasma, including the recently discovered by us phenomenon of Electromagnetic Cascading (EC) and the effect of the EC of three-dimensional dynamics of laser pulses (enhanced/suppressed selffocusing etc.); (d) interaction of high-current electron beams with the ambient plasma in the context of Fast Ignitor (FI) physics, with the emphasis on the nonlinear dynamics of the Weibel instability and beam filamentation.
Date: October 3, 2008
Creator: Shvets, G.
Partner: UNT Libraries Government Documents Department

Simulating Photons and Plasmons in a Three-dimensional Lattice

Description: Three-dimensional metallic photonic structures are studied using a newly developed mixed finite element-finite difference (FE-FD) code, Curly3d. The code solves the vector Helmholtz equation as an eigenvalue problem in the unit cell of a triply periodic lattice composed of conductors and/or dielectrics. The mixed FE-FD discretization scheme ensures rapid numerical convergence of the eigenvalue and allows the code to run at low resolution. Plasmon and photonic band structure calculations are presented.
Date: September 3, 2002
Creator: Pletzer, A. & Shvets, G.
Partner: UNT Libraries Government Documents Department

Electromagnetically Induced Guiding and Superradiant Amplification of Counter-Propagating Lasers in Plasma

Description: The interaction of counter-propagating laser pulses in a plasma in considered. When the frequencies of the two lasers are close, nonlinear modification of the refraction index results in the mutual focusing of the two beams. A short (of order the plasma period) laser pulse can be nonlinearly focused by a long counter-propagating beam which extends over the entire guiding length. It is also demonstrated that a short (< 1/ omega (sub p)) laser pulse can be superradiantly amplified by a counter-propagating long low-intensity pump while remaining ultra-short. Particle-in-Cell simulations indicate that pump depletion can be as high as 40%. This implies that the long pump is efficiently compressed in time without frequency chirping and pulse stretching, making the superradiant amplification an interesting alternative to the conventional method of producing ultra-intense pulses by the chirped-pulse amplification.
Date: August 1, 1998
Creator: Fisch, N.J. & Shvets, G.
Partner: UNT Libraries Government Documents Department

Collisionless Damping of Laser Wakes in Plasma Channels

Description: Excitation of accelerating modes in transversely inhomogeneous plasma channels is considered as an initial value problem. Discrete eigenmodes are supported by plasma channels with sharp density gradients. These eigenmodes are collisionlessly damped as the gradients are smoothed. Using collisionless Landau damping as the analogy, the existence and damping of these "quasi-modes" is studied by constructing and analytically continuing the causal Green's function of wake excitation into the lower half of the complex frequency plane. Electromagnetic nature of the plasma wakes in the channel makes their excitation nonlocal. This results in the algebraic decay of the fields with time due to phase-mixing of plasma oscillations with spatially-varying fequencies. Characteristic decay rate is given by the mixing time, which corresponds to the dephasing of two plasma fluid elements separated by the collisionless skin depth. For wide channels the exact expressions for the field evolution are derived. Implications for electron acceleration in plasma channels are discussed.
Date: August 1, 1998
Creator: Li, X. & Shvets, G.
Partner: UNT Libraries Government Documents Department

Laser-driven Undulator Radiation

Description: An electromagnetic wake of infra-red radiation can be generated by an intense laser pulse, propagating through an underdense plasma in the presence of a magnetostactic undulator. As opposed to undulator radiation from a charged bunch propagating in a periodic magnetic field, here radiation comes from almost stationary plasma electrons, ponderomotively pushed by the laser pulse. Such laser-driven undulator radiation can be produced by either a single ultra-short pulse, or by two frequency-detuned long pulses. In the latter case the difference frequency is efficiently produced by quasi phase-matched optical heterodyning.
Date: August 1, 1998
Creator: Fisch, N.J.; Shvets, G. & and Pukhov, A.
Partner: UNT Libraries Government Documents Department

Raman Forward Scattering in Plasma Channels

Description: Raman scattering instability of an intense laser pulse in a plasma channel proceeds differently than in a homogeneous plasma: the growth rate is reduced and the scaling with the laser intensity modified. These differences, significant even for shallow plasma channels, arise because of the radial shear of the plasma frequency and the existence of the weakly damped hybrid (electrostatic/electromagnetic) modes of the radially inhomogeneous plasma. The interplay of these two effects produces double-peaked spectra for the direct forward scattering in a channel.
Date: November 14, 2000
Creator: Shvets, G. & Li, X.
Partner: UNT Libraries Government Documents Department

Parametric Excitations of Fast Plasma Waves by Counter-propagating Laser Beams

Description: Short- and long-wavelength plasma waves can become strongly coupled in the presence of two counter-propagating laser pump pulses detuned by twice the cold plasma frequency. What makes this four-wave interaction important is that the growth rate of the plasma waves occurs much faster than in the more obvious co-propagating geometry.
Date: March 19, 2001
Creator: Shvets, G. & Fisch, N.J.
Partner: UNT Libraries Government Documents Department

Relativistic Raman instability shifted by half-plasma frequency

Description: A new nonlinear Raman instability in underdense plasma is investigated theoretically. Unlike the usual linear Raman instabilities which grow exponentially in time, this instability takes a finite amount of time to diverse. The explosion time t{sub {infinity}} depends on the initial level of the perturbation. A general set of equations for spatio-temporal evolution of the forward non-linear Raman scattering is derived and its temporal evolution is studied in detail. This new instability results in the generation of forward Raman radiation shifted by half the plasma frequency for laser intensities of order or exceeding 10{sup 18}W/cm{sup 2}, something that has been recently observed.
Date: January 1, 1996
Creator: Shvets, G.; Fisch, N.J. & Rax, J.M.
Partner: UNT Libraries Government Documents Department

Acceleration and Compression of Charged Particle Bunches Using Counter-Propagating Laser Beams

Description: The nonlinear interaction between counter-propagating laser beams in a plasma results in the generation of large (enhanced) plasma wakes. The two beams need to be slightly detuned in frequency, and one of them has to be ultra-short (shorter than a plasma period). Thus produced wakes have a phase velocity close to the speed of light and can be used for acceleration and compression of charged bunches. The physical mechanism responsible for the enhanced wake generation is qualitatively described and compared with the conventional laser wakefield mechanism. The authors also demonstrate that, depending on the sign of the frequency difference between the lasers, the enhanced wake can be used as a ``snow-plow'' to accelerate and compress either positively or negatively charged bunches. This ability can be utilized in an electron-positron injector.
Date: October 17, 2000
Creator: Shvets, G.; Fisch, N. J. & Pukhov, A.
Partner: UNT Libraries Government Documents Department

Electromagnetically Induced Guiding of Counter-propagating Lasers in Plasmas

Description: The interaction of counter-propagating laser pulses in a plasma is considered. When the frequencies of the two lasers are close, nonlinear modification of the refraction index results in the mutual focusing of the two beams. A short (of order the plasma period) laser pulse can also be nonlinearly focused by a long counter-propagating beam which extends over the entire guiding length. This phenomenon of electromagnetically induced guiding can be utilized in laser-driven plasma accelerators.
Date: May 1998
Creator: Shvets, G. & Pukhov, A.
Partner: UNT Libraries Government Documents Department

Transparency of Magnetized Plasma at Cyclotron Frequency

Description: Electromagnetic radiation is strongly absorbed by a magnetized plasma if the radiation frequency equals the cyclotron frequency of plasma electrons. It is demonstrated that absorption can be completely canceled in the presence of a magnetostatic field of an undulator or a second radiation beam, resulting in plasma transparency at the cyclotron frequency. This effect is reminiscent of the electromagnetically induced transparency (EIT) of the three-level atomic systems, except that it occurs in a completely classical plasma. Unlike the atomic systems, where all the excited levels required for EIT exist in each atom, this classical EIT requires the excitation of the nonlocal plasma oscillation. The complexity of the plasma system results in an index of refraction at the cyclotron frequency that differs from unity. Lagrangian description was used to elucidate the physics and enable numerical simulation of the plasma transparency and control of group and phase velocity. This control naturally leads to applications for electromagnetic pulse compression in the plasma and electron/ion acceleration.
Date: March 14, 2002
Creator: Shvets, G. & Wurtele, J.S.
Partner: UNT Libraries Government Documents Department

Magnetic Field Generation through Angular Momentum Exchange between Circularly Polarized Radiation and Charged Particles

Description: The interaction between circularly polarized (CP) radiation and charged particles can lead to generation of magnetic field through an inverse Faraday effect. The spin of the circularly polarized electromagnetic wave can be converted into the angular momentum of the charged particles so long as there is dissipation. We demonstrate this by considering two mechanisms of angular momentum absorption relevant for laser-plasma interactions: electron-ion collisions and ionization. The precise dissipative mechanism, however, plays a role in determining the efficiency of the magnetic field generation.
Date: January 18, 2002
Creator: Shvets, G.; Fisch, N.J. & Rax, J.-M.
Partner: UNT Libraries Government Documents Department

Magnetic Field Generation and Electron Acceleration in Relativistic Laser Channel

Description: The interaction between energetic electrons and a circularly polarized laser pulse inside an ion channel is studied. Laser radiation can be resonantly absorbed by electrons executing betatron oscillations in the ion channel and absorbing angular momentum from the laser. The absorbed angular momentum manifests itself as a strong axial magnetic field (inverse Faraday effect). The magnitude of this magnetic field is calculated and related to the amount of the absorbed energy. Absorbed energy and generated magnetic field are estimated for the small and large energy gain regimes. Qualitative comparisons with recent experiments are also made.
Date: December 12, 2001
Creator: Kostyukov, I.Yu.; Shvets, G.; Fisch, N.J. & Rax, J.M.
Partner: UNT Libraries Government Documents Department

Superradiant pulse compression using free-carrier plasma

Description: Free-carrier plasma can be used as an effective nonlinear medium for pulse compression. In the backward Raman amplifier geometry, the lower-frequency seed can extract most of the long pump energy through the mechanism of nonlinear superradiance. Filamentation is avoided due to strong dependence of the Raman instability growth rate on the wavenumber.
Date: July 21, 2000
Creator: Shvets, G.; Fisch, N. J.; Pukhov, A. & Meyer-ter-Vehn, J.
Partner: UNT Libraries Government Documents Department

Pulse compression in plasma: Generation of femtosecond pulses without CPA

Description: Laser pulses can be efficiently compressed to femtosecond duration when a smaller-frequency short pulse collides with high frequency long pulse in rare plasma, absorbing most of its energy. The mechanism of short pulse amplification is nonlinear superradiance.
Date: July 20, 2000
Creator: Shvets, G.; Fisch, N. J.; Pukhov, A. & Meyer-ter-Vehn, J.
Partner: UNT Libraries Government Documents Department