Abstract
The formation and evolution of post-solitons has been discussed for quite some time both analytically and through the use of particle-in-cell (PIC) codes. It is however only recently that they have been directly observed in laser-plasma experiments. Relativistic electromagnetic (EM) solitons are localised structures that can occur in collisionless plasmas. They consist of a low-frequency EM wave trapped in a low electron number-density cavity surrounded by a shell with a higher electron number-density. Here we describe the results of an experiment in which a 100 TW Ti:sapphire laser (30 fs, 800 nm) irradiates a TMPTA foam target with a focused intensity . A third harmonic ( nm) probe is employed to diagnose plasma motion for 25 ps after the main pulse interaction via Doppler-Spectroscopy. Both radiation-hydrodynamics and 2D PIC simulations are performed to aid in the interpretation of the experimental results. We show that the rapid motion of the probe critical-surface observed in the experiment might be a signature of post-soliton wall motion.
Highlights
A third harmonic probe is employed to diagnose plasma motion for 25 ps after the main pulse interaction via Doppler-Spectroscopy. Both radiation-hydrodynamics and 2D PIC simulations are performed to aid in the interpretation of the experimental results
The hydrodynamic evolution of over-dense foams has been the subject of considerable study in the longer pulse regime and with intensities between 1013–15 W cm−2, the production of shock-like perturbations by ultra-short ultra-intense laser pulses is less well understood
The extra reflected peaks recorded in the experimental results, do not seem to match any phenomena occurring in either the HYADES or the EPOCH calculations and so no explanation can be made about the possible origins of these points
Summary
The hydrodynamic evolution of over-dense foams has been the subject of considerable study in the longer pulse regime (pulse duration >1 ns) and with intensities between 1013–15 W cm−2 (see [1,2,3,4,5,6]), the production of shock-like perturbations by ultra-short ultra-intense laser pulses is less well understood. The formation and evolution of post-solitons has been discussed theoretically and numerically through the use of PIC codes [18,19,20,21,22,23] These phenomena have been directly observed in laser-plasma experiments via proton-probing at relativistic intensities [23,24,25,26], optical self-emission and shadowgraphy [27]. The experiments described and modelled here provide some tentative further evidence of the formation and existence of such solitons as a result of high-intensity laser-plasma interaction, and provide what may be the first direct experimental measurements of post-soliton wall ion velocities via pump-probe Doppler spectroscopy
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