For current state-of-the-art terawatt lasers, the primary laser scattering mechanisms in plasma include Forward Raman Scattering (FRS), excitation of plasma waves, and the self-modulational instability (SMI). Using 2D PIC simulations, we demonstrate the dominance of the FRS in the regime with medium-to-low density plasma and non-relativistic laser fields. However, the use of multi-colored lasers with frequency detuning exceeding the plasma frequency suppresses the FRS. The laser power can then be transmitted efficiently.
With the advance of high power laser technologies, we are approaching the possibility to study strong-field vacuum breakdown and an accompanying electron-positron pair plasma via a quantum electrodynamic (QED) cascade. To reach a high quantum nonlinear factor in the particle rest frame, two different configurations are envisioned either through collision of a laser pulse with an energetic electron beam or collision of two laser pulses. Producing QED pair plasmas all optically is generally believed to require next generation laser technology that can output 100 PW power. Based on the electron-beam-laser collision setup, our recent work, however, shows that signatures of collective pair plasma effects appear in exquisite detail through plasma-induced frequency upshifts in the laser spectrum. Remarkably, these signatures can be detected even in a pair plasma created by passing a dense multi-tens-GeV electron beam through a multi-PW laser pulse. This method substantially reduces the already low laser intensity requirement, and the use of lower laser intensities, compared to all-optical methods, significantly makes the QED collective effects easier to observe. Strong-field quantum and collective pair plasma effects can thus be explored with existing technology, providing vital information for QED cascades in general and QED plasma regimes in particular.
Laser amplification through plasma-based techniques might overcome the thermal damage limit of conventional materials, thereby enabling the next generation of laser intensities. The leading plasma-based method is Raman compression: a long laser pump decays into a plasma wave and a counterpropagating short laser seed pulse, which, capturing the pump energy, reaches extreme intensities. The technological requirements on the seed are severe: it must be very sharp and matched properly in frequency. To sharpen the seed pulse, we propose a laser-controlled, super-fast plasma shutter technique, analogous to electromagnetically induced transparency (EIT) in atoms. We further show that the laser seed may even be replaced by a stationary plasma wave seed. In the important pump-depletion regime, the plasma-wave initiated output pulse approaches the self-similar attractor solution for the corresponding laser seed, with the frequency match automatic. These techniques also work with partially coherent pumps. Actually, a partially coherent pump can even advantageously suppress the noise-seeded spontaneous Raman amplification which is responsible for premature pump depletion.
Conference Committee Involvement (1)
Coherent and Incoherent Radiation Sources based on Relativistic Plasma Waves V
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