Radiation sources from Langmuir waves has been a topic of interest for their relevance to experimental approaches in plasma laboratories as well as for estimating physical models to explain cosmic radio bursts. Since the mechanism for converting energy from electrostatic Langmuir waves to electromagnetic waves is complex, diverse scenarios of such energy conversion have been studied, e.g. mode conversion, antenna radiation, nonlinear scattering, etc. Previously, we introduced a novel perspective of plasma dipole oscillation (PDO) which generates strong radiation bursts at the plasma frequency and high harmonics. In this paper, we report our discovery of radiation that result from electron-laser beam driven Langmuir waves and their interactions. In 2-D PIC simulations, we have observed that obliquely colliding Langmuir waves or even a single Langmuir wave generate localized radiation sources at the plasma frequency and high harmonics. These mechanisms differ from conventional two-plasmon mergers, where only the second harmonic of the plasma frequency is dominant: a strong radiation is observed even at the fundamental harmonic. In addition, from 3-D PIC simulations of electron laser beam driven plasma oscillators in magnetized plasma, the radiation from a local plasma oscillator, i.e. PDO, is found to be robust with diverse spectral peaks at the X-mode and the upper-hybrid mode. Nonlinear theory demonstrates that the relative strength of the harmonics of the plasma frequency depends on the shape of the PDO. The studies imply that the PDO has a more complicated internal structure than the simple model of a solid charge. We discuss the potential of the PDO generated from electron-beam driven plasmas or laser-driven plasmas as a radiation source and its relevance to cosmic radio bursts.
Laser-plasma interactions have many theoretical and technological applications. One is the use of coherently accelerated electrons to provide novel sources of THz radiation. Our research focuses on simulating the cross/self-interactions between two high intensity, ultra-short, counter propagating and detuned laser pulses and an initial neutral target for controlled ionization. Unlike our previous studies of laser-matter interaction over preformed plasma, we explore the injection and collision of laser pulses to induce background plasma driven by the self-guided laser wakefield mechanism, which is then used to perturb the plasma resulting in induced dipole oscillations leading to transverse radiation. Inducing a cylindrical spatial plasma column within the laser beam radius regime provides a stable, spatially localized plasma channel. The emitted radiation from the plasma dipole oscillation (PDO) will not be affected by surrounding plasma absorption, resulting in effective radiation distribution. Results include 3D EM-PIC simulations and a comparison of the self- ionizing plasma against the preformed plasma to assess the efficiency of the mechanisms.
It is well known that an infinite homogeneous Langmuir wave, formed by accelerating charged particles, it does not emit electromagnetic radiation because of its electrostatic nature, which is represented by the zero curl of the electric field. To realise emission, the plasma density must be tailored such that the Langmuir wave takes on a non-zero component of the curl of the electric field. The mechanisms of inverse mode conversion or travelling wave antennae leads to emission of radiation. In these mechanisms, the emphasis is on energy conversion of the Langmuir ‘wave’ to an electromagnetic wave. However, an interesting way to cause the plasma wave to emit radiation is to isolate a single ‘oscillator’ composed of a localized plasma block, i.e., a plasma dipole. An outstanding question in the realization of this idea is how to isolate the plasma oscillation from the Langmuir wave. To answer this question, we propose a novel idea of colliding detuned counter-propagating laser pulses in plasma. Simulation results show that radiation is emitted from the isolated plasma dipole.
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