His primary fields of study were about the free electron lasers and the theory of electron beam-plasma instabilities (Cherenkov instability) which is the base of plasma UHF electronics, he has extended his research interests to the nonlinear optics of laser-plasma interaction including phenomena such as self-focusing, terahertz generation, modulational and Raman instabilities, nonlinear modes, harmonics generation and solitons. Also, he has some theoretical studies about the nonlinear effects during interaction of laser with media including metallic nanoparticles which is a new exotic branch of Plasmonics. Additionally, he has started to study Cherenkov instability of electron bunches interacting with Parcell-Smith systems including a graphene layer which can lead to the terahertz radiation. The thesis topic of two master students of him is related to this problem. Recently, he has started some experimental investigations about atmospheric and low pressure discharges which include plasma antenna, nanoparticles synthesis by plasma discharge in liquids, influence of various discharges on hydrophobicity or hydrophilicity properties and plasma medicine as well. The results of his investigations during his career as a university professor are more than 30 qualified journal articles in different areas of plasma physics and plasmonics.
A linear theory for the parametric instability of a free-electron laser with a longitudinal electrostatic wiggler is presented. A space-charge wave and a predominantly transverse magnetic wave guide mode are excited when a relativistic electron beam is passed through a static spatially periodic longitudinal electric wiggler. The thick annular electron beam is contained in a cylindrical metal wave guide and an axial magnetic field of arbitrary magnitude. An expression for the wave-field components is derived and solved numerically along with the dispersion relations for the eigenmodes of a wave guide containing a magnetized annular electron beam. Effects of the variation of the beam radii, the axial magnetic field, and electron beam kinetic energy on the growth rate, efficiency, radiation wavelength, and the required pump wavelength are studied. A suitable range of parameters for the generation of millimeter wave is indicated.
The problem of the development of instability in a bounded spatial region due to the collective Cherenkov effect or the anomalous Doppler effect is studied in the linear approximation. Threshold conditions for the onset of the convective and absolute instabilities of different longitudinal modes and their growth rates are determined with allowance for reflections from the boundaries of the system. The dynamics of the development of an initial perturbation during convective instability is simulated.
The problem of stimulated emission from a relativistic electron beam in an external electrostatic pump field is studied. A set of nonlinear time-dependent equations for the spatiotemporal dynamics of the undulator radiation amplitude and the amplitude of the beam space charge field is derived. The beam electrons are described by a modified version of the macroparticle method. The regimes of the single-particle and collective Cherenkov effects during convective and absolute instabilities are considered. The nonlinear dynamics of radiation pulses emitted during the instabilities of the beam in its interaction with the forward and backward electromagnetic waves is investigated.
The study of the dynamics of the interaction of intense electromagnetic fields with metallic nanoparticles is a great interest of some applied nonlinear phenomena in nano-optics and plasmonics. These phenomena include harmonics generation, nano-focusing, self-focusing, nonlinear modes and nano-waveguiding. Using a relativistic modified Drude model, we analytically solve the motion equations of conduction electrons of spherical nanoparticles in a linear chain interacting with a linearly-polarized laser propagating perpendicular to the symmetry axis of the chain. The mutual interaction of each particle with two adjacent neighbors has been considered in the dipole-dipole interaction regime. By means of a perturbative approach, the motion equations related to the first, second and third harmonics of electromagnetic fields are solved. Numerical studies are carried out for a linear chain including 10 of 10 nm radius gold nanoparticles. The effect of interparticle separation and laser polarization on the nonlinear dynamics of the system has been investigated. It is shown that the interaction of particles causes a blueshift for the plasmon resonance of the system for the polarization of laser where the electric field is perpendicular to the symmetry axis of the chain. In the parallel case of the laser electric field, plasmon resonance frequency experiences a redshift for the first and third harmonics displacements, whereas it blueshifts for the second harmonics due to the interparticle interactions. Also, the interaction of particles causes a decrease in the amplitude of the conduction electrons at the plasmon resonance region for the perpendicular state of laser polarization and its increase for the parallel state.