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Register a new userResonance absorption of a broadband laser pulse
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Broad bandwidth, infrared light sources have the potential to revolutionize inertial confinement fusion (ICF) by suppressing laser-plasma instabilities. There is, however, a tradeoff: The broad bandwidth precludes high efficiency conversion to the ultraviolet, where laser-plasma interactions are weaker. Operation in the infrared could intensify the role of resonance absorption, an effect long suspected to be the shortcoming of early ICF experiments. Here we present simulations exploring the effect of bandwidth on resonance absorption. In the linear regime, bandwidth has little effect on resonance absorption; in the nonlinear regime, bandwidth suppresses enhanced absorption resulting from the electromagnetic decay instability. These findings evince that regardless of bandwidth, an ICF implosion will confront at least linear levels of resonance absorption.
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Absorption covers the physical processes which convert intense photon flux into energetic particles when a high-power laser illuminates optically-thick matter. It underpins important petawatt-scale applications today, e.g., medical-quality proton beam production. However, development of ultra-high-field applications has been hindered since no study so far has described absorption throughout the entire transition from the classical to the quantum electrodynamical (QED) regime of plasma physics. Here we present a model of absorption that holds over an unprecedented six orders-of-magnitude in optical intensity and lays the groundwork for QED applications of laser-driven particle beams. We demonstrate 58% efficient gamma-ray production at $1.8times 10^{25}~mathrm{W~ cm^{-2}}$ and the creation of an anti-matter source achieving $4times 10^{24} mathrm{positrons} mathrm{cm^{-3}}$, $10^{6}~times$ denser than of any known photonic scheme. These results will find applications in scaled laboratory probes of black hole and pulsar winds, gamma-ray radiography for materials science and homeland security, and fundamental nuclear physics.
Electronic parametric instabilities of an ultrarelativistic circularly polarized laser pulse propagating in underdense plasmas are studied by numerically solving the dispersion relation which includes the effect of the radiation reaction force in laser-driven plasma dynamics. Emphasis is placed on studying the different modes in the laser-plasma system and identifying the absolute and convective nature of the unstable modes in a parameter map spanned by the normalized laser vector potential and the plasma density. Implications for the ultraintense laser-plasma experiments are pointed out.
In this proceeding, we show that when the drive laser pulse overlaps the trapped electrons in a laser wakefield accelerator (LWFA), those electrons can gain energy from direct laser acceleration (DLA) over extended distances despite the evolution of both the laser and the wake. Through simulations, the evolution of the properties of both the laser and the electron beam is quantified, and then the resonance condition for DLA is examined in the context of this change. We find that although the electrons produced from the LWFA cannot continuously satisfy the DLA resonance condition, they nevertheless can gain a significant amount of energy from DLA.
Since it is possible to form laser pulses with a frequency much larger than the frequency of visible light, Prof. T.Tajima proposed using such pulse to accelerate the particles at its injection into the crystal. Here, the wakefield excitation in the metallic-density plasma and the electron acceleration by laser pulse are simulated. The accelerating gradient has been ob-tained approximately 3TV/m. It is shown that, as in ordinary plasma, with time beam-plasma wakefield acceleration is added to laser wakefield acceleration.
Electrons at the surface of a plasma that is irradiated by a laser with intensity in excess of $10^{23}~mathrm{W}mathrm{cm}^{-2}$ are accelerated so strongly that they emit bursts of synchrotron radiation. Although the combination of high photon and electron density and electromagnetic field strength at the plasma surface makes particle-particle interactions possible, these interactions are usually neglected in simulations of the high-intensity regime. Here we demonstrate an implementation of two such processes: photon absorption and stimulated emission. We show that, for plasmas that are opaque to the laser light, photon absorption would cause complete depletion of the multi-keV region of the synchrotron photon spectrum, unless compensated by stimulated emission. Our results motivate further study of the density dependence of QED phenomena in strong electromagnetic fields.
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