17 research outputs found
Enhanced relativistic harmonics by electron nanobunching
It is shown that when an few-cycle, relativistically intense, p-polarized
laser pulse is obliquely incident on overdense plasma, the surface electrons
may form ultra-thin, highly compressed layers, with a width of a few
nanometers. These electron "nanobunches" emit synchrotron radiation coherently.
We calculate the one-dimensional synchrotron spectrum analytically and obtain a
slowly decaying power-law with an exponent of 4/3 or 6/5. This is much flatter
than the 8/3 power of the BGP (Baeva-Gordienko-Pukhov) spectrum, produced by a
relativistically oscillating bulk skin layer. The synchrotron spectrum cut-off
frequency is defined either by the electron relativistic -factor, or by
the thickness of the emitting layer. In the numerically demonstrated, locally
optimal case, the radiation is emitted in the form of a single attosecond
pulse, which contains almost the entire energy of the full optical cycle.Comment: to appear in Physics of Plasma
Harmonic Generation from Relativistic Plasma Surfaces in Ultra-Steep Plasma Density Gradients
Harmonic generation in the limit of ultra-steep density gradients is studied
experimentally. Observations demonstrate that while the efficient generation of
high order harmonics from relativistic surfaces requires steep plasma density
scale-lengths () the absolute efficiency of the harmonics
declines for the steepest plasma density scale-length , thus
demonstrating that near-steplike density gradients can be achieved for
interactions using high-contrast high-intensity laser pulses. Absolute photon
yields are obtained using a calibrated detection system. The efficiency of
harmonics reflected from the laser driven plasma surface via the Relativistic
Oscillating Mirror (ROM) was estimated to be in the range of 10^{-4} - 10^{-6}
of the laser pulse energy for photon energies ranging from 20-40 eV, with the
best results being obtained for an intermediate density scale-length
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Relativistic laser plasmas for novel radiation sources
Relativistic laser-plasma interaction results in new sources of short-pulsed x-ray radiation. Here we consider two options. The first one is betatron radiation of electrons accelerated in underdense plasmas and oscillating in transverse fields of the laser wake. This radiation is incoherent and broadband, the pulse duration is comparable with that of the driving laser. The second option is the high harmonic generation (HHG) from overdense plasma surfaces. This radiation is coherent. The relativistic high harmonics are phase locked and emerge in the form of (sub-)attosecond pulses. One- and three-dimensional regimes of relativistic HHG from overdense plasmas are considered
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Influence of Surface Waves on Plasma High-Order Harmonic Generation
The influence of surface plasma waves on high-order harmonic generation from the interaction of intense lasers with overdense plasma is analyzed. It is shown that the surface waves lead to the emission of harmonics away from the optical axis, whereas the high-order on-axis harmonics are lowered in intensity. Our simulation results indicate that surface plasma wave generation plays a crucial role in surface high-order harmonic generation experiments. Furthermore, a novel surface plasma wave generation process different from the well-known two-surface wave decay is observed in the highly relativistic regime
Relativistic high harmonics and (sub-)attosecond pulses: relativistic spikes and relativistic mirror
Using particle-in-cell simulations, we study high harmonic generation
from overdense plasmas in the relativistic regime. Different incidence
angles as well as different laser polarizations are considered and
scalings are recovered. It is shown that the theory of relativistic
spikes and the BGP power-law spectra [Phys. Rev. E 74, 046404 (2006)] describes well the normal incidence
and s-polarized obliquely
incident laser pulses. In the case of p-polarized laser pulses,
exceptions from the BGP theory can appear when the quasi-static vector
potential build-up at the plasma boundary becomes equal to that of the
laser. In this case, the spectrum flattens significantly and has a
lower cutoff