The expansion of electromagnetic post-solitons emerging from the interaction of a 30 ps, 3 × 10 18 W cm −2 laser pulse with an underdense deuterium plasma has been observed up to 100 ps after the pulse propagation, when large numbers of post-solitons were seen to remain in the plasma. The temporal evolution of the post-solitons has been accurately characterized with a high spatial and temporal resolution. The observed expansion is compared to analytical models and three dimensional particle-in-cell results providing indication of the polarisation dependence of the postsoliton dynamics.

We present a comprehensive numerical study of the dynamics of an intense laser pulse as it propagates through an underdense plasma in two and three dimensions. By varying the background plasma density and the polarization of the laser beam, significant differences are found in terms of energy transport and dissipation, in agreement with recently reported experimental results. Below the threshold for relativistic self-focusing, the plasma and laser dynamics are observed to be substantially insensitive to the initial laser polarization, since laser transport is dominated by ponderomotive effects. Above this threshold, relativistic effects become important, and laser energy is dissipated either by plasma heating (p-polarization) or by trapping of electromagnetic energy into plasma cavities (s-polarization) or by a combination of both (circular polarization). Besides the fundamental interest of this study, the results presented are relevant to applications such as plasma-based accelerators, x-ray lasers, and fast-ignition inertial confinement fusion.

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Laser wakefield acceleration (LWFA) is a promising technique to build compact and powerful particle accelerators. In such accelerators, the electric fields required to accelerate charged particles are sustained by electron density modulations in the plasma. The plasma wave modulating the electron density may be excited by an intense laser pulse. However, propagation of intense laser pulse in plasma is subject to various instabilities which result in significant losses of laser energy, reducing the efficiency of wakefield generation. Using a train of lower intensity pulses instead of a single higher intensity pulse appears to be a more efficient scheme for LWFA. Here we have studied this alternative scheme by applying an ultra-short femtosecond Gaussian laser beam consisting pulse train of a various number of pulses in different cases to underdense plasma. The plasma density modulation and strength of the resulting wakefield have been compared in various cases of multi-pulse and single-pulse lasers, for the same amount of input energies. Here we demonstrate that applying multi-laser pulses of optimally selected lower intensities and proper spacing leads to stronger wakefield generation and more efficient electron acceleration compared to the case of a single pulse of higher energy.

The authors discuss polarization and intensity fluctuations in helium-neon lasers polarized by using permanent magnets. (AIP)