J. Parashar

Effect of magnetic field on terahertz generation via laser interaction with a carbon nanotube array

An amplitude-modulated laser, in the presence of a static magnetic field, interacts with an array of carbon nanotubes embedded on a metallic surface. The laser exerts a ponderomotive force on the free electrons of carbon nanotubes at twice the modulation frequency that falls in the terahertz (THz) range. Each nanotube acts as an oscillatory electric dipole, producing THz radiations. The presence of magnetic field shifts the resonance condition and provides tunability. The THz radiation power increases with magnetic field strength.

Stimulated Raman scattering of laser from periodically spaced nanoparticles

A periodic lattice of nanoparticles supports an electrostatic mode of space charge oscillations with frequency lying in a narrow band and varying periodically around ωpe∕3 with the wave number, where ωpe is the plasma frequency of electrons inside a nanoparticle. A laser impinged on such a lattice undergoes stimulated Raman scattering producing backward sideband electromagnetic radiation. The growth rate is maximum around the pump frequency ω0=0.75ωpe, and then decreases gradually.

Laser beat wave excitation of terahertz radiation in a plasma slab

Terahertz (THz) radiation generation by nonlinear mixing of lasers, obliquely incident on a plasma slab is investigated. Two cases are considered: (i) electron density profile is parabolic but density peak is below the critical density corresponding to the beat frequency, (ii) plasma boundaries are sharp and density is uniform. In both cases, nonlinearity arises through the ponderomotive force that gives rise to electron drift at the beat frequency. In the case of inhomogeneous plasma, non zero curl of the nonlinear current density gives rise to electromagnetic THz generation. In case of uniform plasma, the sharp density variation at the plasma boundaries leads to radiation generation. In a slab width of less than a terahertz wavelength, plasma density one fourth of terahertz critical density, laser intensities ∼1017 W/cm2 at 1 μm, one obtains the THz intensity ∼1 GW/cm2 at 3 THz radiation frequency.

Effect of self-focusing on laser third harmonic generation in a clustered gas

An intense Gaussian laser beam propagating through a gas embedded with atomic clusters creates a nanoplasma medium which supports self focusing of the laser beam. The laser beam produces a third harmonic due to nonlinear electron response. The efficiency of the process is sensitive to the focusing of the fundamental laser beam. The harmonic generation yield increases as the clusters expand under hydrodynamic pressure and attains a maximum at the instant when plasma density inside clusters equals three times the critical density. Further, the self-focusing of the laser enhances the efficiency of harmonic generation by ten times.

Electromagnetic-wave-pumped free-electron laser in a plasma channel

An intense short laser pulse or a millimetre wave propagating through a plasma channel may act as a wiggler for the generation of shorter wavelengths. When a relativistic electron beam is launched into the channel from the opposite direction, the laser radiation is Compton/Raman backscattered to produce coherent radiation at shorter wavelengths. The scheme, however, requires a superior beam quality with energy spread less than 1% in the Raman regime.

Second harmonic generation from a metallic thin film by an obliquely incident laser

The generation of second harmonic by a laser incident obliquely on a thin metal film grown on a glass substrate is studied. The laser imparts a nonlinear current to the electrons of the metal film, which generates the second harmonic in the reflected component. The second harmonic radiation is sensitive to angle of incidence and film thickness. For a particular set of parameters, the second harmonic amplitude is ~23% of the incident laser amplitude.

Surface plasma waves over bismuth-vacuum interface

AbstractA surface plasma wave (SPW) over bismuth-vacuum interface has a signature of mass anisotropy of free electrons. For SPW propagation along the trigonal axis there is no birefringence. The frequency cutoff of SPW

Laser excitation of surface plasma waves over a diffuse plasma boundary

\omega _{cutoff} = \omega _p /\sqrt {2(\varepsilon _L + \varepsilon )}