14 research outputs found
Strongly coupled large-angle stimulated Raman scattering of short laser pulses in plasma-filled capillaries
Strongly coupled large-angle stimulated Raman scattering (LA SRS) of a short
intense laser pulse proceeds in a plane plasma-filled capillary differently
than in a plasma with open boundaries. Oblique mirror reflections off capillary
walls partly suppress the lateral convection of scattered radiation and
increase the growth rate of the instability: the convective gain of the LA SRS
falls with an angle much slower than in an unbounded plasma and even for the
near-forward SRS can be close to that of the direct backscatter. The long-term
evolution of LA SRS in the interior of the capillary is dominated by
quasi-one-dimensional leaky modes, whose damping is related to the transmission
of electromagnetic waves through capillary walls.Comment: 11 pages, 6 figures; to be submitted to Physics of Plasma
Nonlinear evolution of the plasma beatwave: Compressing the laser beatnotes via electromagnetic cascading
The near-resonant beatwave excitation of an electron plasma wave (EPW) can be
employed for generating the trains of few-femtosecond electromagnetic (EM)
pulses in rarefied plasmas. The EPW produces a co-moving index grating that
induces a laser phase modulation at the difference frequency. The bandwidth of
the phase-modulated laser is proportional to the product of the plasma length,
laser wavelength, and amplitude of the electron density perturbation. The laser
spectrum is composed of a cascade of red and blue sidebands shifted by integer
multiples of the beat frequency. When the beat frequency is lower than the
electron plasma frequency, the red-shifted spectral components are advanced in
time with respect to the blue-shifted ones near the center of each laser
beatnote. The group velocity dispersion of plasma compresses so chirped
beatnotes to a few-laser-cycle duration thus creating a train of sharp EM
spikes with the beat periodicity. Depending on the plasma and laser parameters,
chirping and compression can be implemented either concurrently in the same, or
sequentially in different plasmas. Evolution of the laser beatwave end electron
density perturbations is described in time and one spatial dimension in a
weakly relativistic approximation. Using the compression effect, we demonstrate
that the relativistic bi-stability regime of the EPW excitation [G. Shvets,
Phys. Rev. Lett. 93, 195004 (2004)] can be achieved with the initially
sub-threshold beatwave pulse.Comment: 13 pages, 11 figures, submitted to Physical Review
Physics of Quasi-Monoenergetic Laser-Plasma Acceleration of Electrons in the Blowout Regime
Medical genetic
ALL-OPTICAL CONTROL OF ELECTRON TRAPPING IN TAPERED PLASMAS AND CHANNELS
The radiation pressure of a multi-terawatt, sub-100 fs laser pulse propagating in an under-dense plasma causes complete electron cavitation. The resulting electron density “bubble” guides the pulse over many Rayleigh lengths, leaving the background ions unperturbed while maintaining GV/cm-scale accelerating and focusing gradients. The shape of the bubble, and, hence, the wakefield potentials, evolve slowly, in lockstep with the optical driver. This dynamic structure readily traps background electrons. The electron injection process can thus be controlled by purely optical means
Improved particle statistics for laser-plasma self-injection simulations
We describe methods for improving the accuracy of injected particle beams by selectively enhancing the particle statistics in particle-in-cell simulations, using reduced model computations as a guide. We demonstrate convergence of key beam parameters in two dimensions, and show improved noise properties in three dimensions
Chapter Physics of Quasi-Monoenergetic Laser-Plasma Acceleration of Electrons in the Blowout Regime
Medical genetic
Accordion Effect in Plasma Channels: Generation of Tunable Comb-Like Electron Beams
Propagating a short, relativistically intense laser pulse in a plasma channel makes it possible to generate comb-like electron beams for advanced radiation sources. The ponderomotive force of the leading edge of the pulse expels all electrons facing the pulse. The bare ions attract the ambient plasma electrons, forming a closed bubble of electron density confining the pulse tail. The cavity of electron density evolves slowly, in lock-step with the optical driver, and readily traps background electrons. The combination of a bubble (a self-consistently maintained, “soft” hollow channel) and a preformed channel forces transverse flapping of the laser pulse tail, causing oscillations in the bubble size. The resulting periodic injection produces a sequence of background-free, quasi-monoenergetic bunches of femtosecond duration. The number of these spectral components, their charge, energy, and energy separation is sensitive to the channel radius and pulse length. Accumulation of noise (continuously injected charge) can be prevented using a negatively chirped drive pulse with a bandwidth close to a one-half of the carrier wavelength. As a result of dispersion compensation, self-steepening of the pulse is reduced, and continuous injection almost completely suppressed. This level of control on a femtosecond time scale is hard to achieve with conventional accelerator techniques. These comb-like beams can drive high-brightness, tunable, multi-color -ray sources