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Type-III-burst radio signals can be mimicked in the laboratory via laser-plasma interaction. Instead of an electron beam generating Langmuir waves (LWs) in the interplanetary medium, the LWs are created by a laser interacting with a millimeter-sized plasma through the stimulated Raman instability. In both cases, the LWs feed the Langmuir decay instability which scatters them in several directions. The resulting LWs may couple to form electromagnetic emission at twice the plasma frequency, which has been detected in the interplanetary medium, and recently in a laboratory laser experiment [Marquès et al., Phys. Rev. Lett. 124, 135001 (2020)]. This article presents the first numerical analysis of this laser configuration using particle-in-cell simulations, providing details on the wave spectra that are too difficult to measure in experiments. The role of some parameters is addressed, with a focus on laser intensity, in order to illustrate the behavior of the electromagnetic emission's angular distribution and polarization. [ABSTRACT FROM AUTHOR]

Red and yellow lines identify the wave-vectors produced by Raman [Eq. (1)] and LDI [Eq. (2)], respectively. Red and yellow lines identify the wave-vectors produced by SRS [Eq. (1)] and by the first LDI step [Eq. (2)], respectively. Magenta lines identify the wave-vectors produced by LDI [Eq. (3)]. [Extracted from the article]

The shock ignition concept implies laser pulse intensities higher than 1015 W/cm2 (at the wavelength of 351 nm), which is the commonly accepted limit where the inverse bremsstruhlung absorption dominates. The transition from collisional to collisionless absorption in laser plasma interactions at higher intensities is studied in the present paper with the help of large scale one-dimensional particle-in-cell simulations. The initial parameters are defined by the hydrodynamic simulations corresponding to recent experiments. The simulations predict that a quasi-steady regime of laser plasma interaction is attained where the total laser energy absorption stays on the level of ∼65% in the laser intensity range 1015-1016 W/cm2. However, the relation between the collisional and collisionless processes changes significantly. This is manifested in the energy spectrum of electrons transporting the absorbed laser energy and in the spectrum of the reflected laser light. [ABSTRACT FROM AUTHOR]

Two-dimensional particle-in-cell simulations of laser-plasma interaction using a plane-wave geometry show strong bursty stimulated Brillouin backscattering, rapid filamentation, and subsequent plasma cavitation. It is shown that the cavitation is not induced by self-focusing. The electromagnetic fields below the plasma frequency that are excited are related to transient soliton-like structures. At the origin of these solitons is a three-wave decay process exciting new modes in the plasma. The cavitation is responsible for a strong local reduction of the reflectivity and goes along with an efficient but transient heating of the electrons. Once heating ceases, transmission starts to increase. Local as well as global average reflectivities attain a very low value due to strong plasma density variations brought about by the cavitation process. On the one hand, the simulations confirm the existence of a new mechanism of cavity and soliton formation in nonrelativistic laser-plasma interaction in two dimensions, which was shown to exist in one-dimensional simulations [S. Weber, C. Riconda, and V. T. Tikhonchuk, Phys. Rev. Lett. 94, 055005 (2005)]. On the other hand, new aspects are introduced inherently related to the additional degree of freedom. [ABSTRACT FROM AUTHOR]

A new experimental platform based on laser-plasma interaction is proposed to explore the fundamental processes of wave coupling at the origin of interplanetary radio emissions. It is applied to the study of electromagnetic (EM) emission at twice the plasma frequency (2ωp) observed during solar bursts and thought to result from the coalescence of two Langmuir waves (LWs). In the interplanetary medium, the first LW is excited by electron beams, while the second is generated by electrostatic decay of Langmuir waves. In the present experiment, instead of an electron beam, an energetic laser propagating through a plasma excites the primary LW, with characteristics close to those at near-Earth orbit. The EM radiation at 2ωp is observed at different angles. Its intensity, spectral evolution, and polarization confirm the LW-coalescence scenario. [ABSTRACT FROM AUTHOR]

We investigate the formation of a laser-produced magnetized jet under conditions of a varying mass ejection rate and a varying divergence of the ejected plasma flow. This is done by irradiating a solid target placed in a 20 T magnetic field with, first, a collinear precursor laser pulse (1012 W/cm²) and, then, a main pulse (1013 W/cm²) arriving 9-19 ns later. Varying the time delay between the two pulses is found to control the divergence of the expanding plasma, which is shown to increase the strength of and heating in the conical shock that is responsible for jet collimation. These results show that plasma collimation due to shocks against a strong magnetic field can lead to stable, astrophysically relevant jets that are sustained over time scales 100 times the laser pulse duration (i.e., >70 ns), even in the case of strong variability at the source. [ABSTRACT FROM AUTHOR]