Self-focusing, compression and collapse of ultrashort weakly-relativistic Laguerre Gaussian lasers in near-critical plasma

Wilson, T C and Sheng, Z-M and McKenna, P and Hidding, B (2023) Self-focusing, compression and collapse of ultrashort weakly-relativistic Laguerre Gaussian lasers in near-critical plasma. Journal of Physics Communications, 7 (3). 035002. ISSN 2399-6528 (https://doi.org/10.1088/2399-6528/acbf05)

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Abstract

Simultaneous self-focusing and compression of ultrashort weakly-relativistic Laguerre-Gaussian laser pulses in dense plasma is investigated theoretically and numerically. A simple theoretical model is developed and used to identify parameter regimes of interest, and then three-dimensional particle-in-cell simulations are carried out to examine the physics in detail. Rapid self-focusing and compression are observed, leading to pulse collapse even for laser pulse energy at the ten millijoule level. Long-lived ring-shaped post-soliton structures are left at the location of the first collapse, and the residual laser energy is scattered into the plasma. Filamentation and re-focusing occur beyond this point, the structure of which depends on the beam parameters but is observed to be only weakly dependent upon the mode of the laser. Circularly-polarised light is found to produce particulary symmetric plasma density structures. In all cases, bursts of MeV electrons with thermal-like spectra are observed at points of collapse.

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