The layered crystal formation in dusty plasma medium depicted by the Yukawa interaction amidst dust has been investigated using molecular dynamics simulations. The multilayer structures are shown to form in the presence of a combined gravitational and external electric field force (representing the sheath field in experiments) along theẑ direction. A detailed study of the dependence of the number of crystal layer formation, their width etc., on various system parameters (viz., the external field profile and the screening length of Yukawa interaction) have been analyzed. The structural properties of crystalline bilayers have been studied in detail identifying their structures with the help of pair correlation function and Voronoi diagrams. It has been shown that the crystalline layers undergo a structural phase transition from hexagonal (often also referred to as triangular) to square lattice configurations. A reentrant phase transition from hexagonal to square (and rhombic) structure has been observed in the simulations.

The excitation of electrostatic waves in plasma by laser electromagnetic (EM) pulse is important as it provides a scheme by which the power from the laser EM field can be transferred into the plasma medium. The paper presents a fundamentally new ponderomotive pressure-driven mechanism of excitation of electrostatic waves in an overdense magnetized plasma by a finite laser pulse. Particle-in-cell simulations using the EPOCH-4.17.10 framework have been utilized for the study of a finite laser pulse interacting with a magnetized overdense plasma medium. The external magnetic field is chosen to be aligned parallel to the laser propagation direction. In this geometry, the EM wave propagation inside the plasma is identified as whistler or R and L waves. The group velocity of these waves being different, a clear spatial separation of the R and L pulses are visible. In addition, excitation of electrostatic perturbation associated with the EM pulses propagating inside the plasma is also observed. These electrostatic perturbations are important as they couple laser energy to the plasma medium. The excitation of electrostatic oscillations are understood here by a fundamentally new mechanism of charge separation created by the difference between the ponderomotive force (of the EM pulse) felt by the two plasma species, viz., the electrons and the ions in a magnetized plasma.

The mechanism of harmonic generation in both O- and X-mode configurations for a magnetized plasma has been explored here in detail with the help of particle-in-cell simulations. A detailed characterization of both the reflected and transmitted electromagnetic radiation propagating in the bulk of the plasma has been carried out for this purpose. The efficiency of harmonic generation is shown to increase with the incident laser intensity. A dependency of harmonic efficiency has also been found on magnetic field strength. This work demonstrates that there is an optimum value of the magnetic field at which the efficiency of harmonic generation maximizes. The observations are in agreement with theoretical analysis. For the O-mode configuration, this is compelling as the harmonic generation provides for a mechanism by which laser energy can propagate inside an overdense plasma region.

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Collective response of the plasma medium is well known and has been explored extensively in the context of dusty plasma medium. On the other hand, individual particle response associated with the collisional character giving rise to dissipative phenomena has not been explored adequately. In this paper two-dimensional (2-D) molecular dynamics (MD) simulation of dust particles interacting via Yukawa potential has been considered. It has been shown that disturbances induced in a dust crystal elicit both collective and single particle responses. Generation of a few particles moving at speeds considerably higher than acoustic and/or shock speed ( excited by the external disturbance) are observed. This is an indication of a single particle response. Furthermore, as these individual energetic particles propagate, the dust crystal is observed to crack along their path. Initially when the energy is high these particles generate secondary energetic particles by collisional scattering process. However, ultimately as these particles slow down they excite collective response in the dust medium at secondary locations in a region which is undisturbed by the primary external disturbance. The condition when the cracking of the crystal stops and collective excitations get initiated has been identified quantitatively. The trailing collective primary disturbances would thus often encounter a disturbed medium with secondary and tertiary collective perturbations, thereby suffering significant modification in its propagation. It is thus clear that there is an interesting interplay (other than mere dissipation) between the single particle and collective response which governs the dynamics of any disturbance introduced in the medium.