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Malik A.K.,University of Rochester | Malik A.K.,Chaudhary Charan Singh University | Singh K.P.,Singh Simutech Pvt. Ltd.
Laser and Particle Beams | Year: 2015

We propose a mechanism of highly focused, tunable and high-intensity terahertz (THz) radiation generation by frequency-mixing of two super-Gaussian lasers with frequencies ω1, ω2 and wave numbers k 1, k 2 (laser profile index p > 2) in a corrugated plasma in the presence of external static magnetic field . In this process, a strong nonlinear ponderomotive force is offered to the plasma electrons at frequency ω′ = ω1 - ω2 and wave number k′ = k 1 - k 2 by laser beams. The ponderomotive force results in a strong, controllable nonlinear transverse oscillatory current, which can be optimized by optimizing the external magnetic field, ripple parameters, and laser indexes. This controllable current produces focused and intense THz radiation of tunable frequency and power along with a remarkable efficiency ∼25%. Copyright © Cambridge University Press 2015. Source

Malik A.K.,Ccs University | Singh K.P.,Singh Simutech Pvt. Ltd. | Sajal V.,Jaypee Institute of Information Technology
Physics of Plasmas | Year: 2014

A mechanism of efficient and highly focused terahertz (THz) radiation generation by photo-mixing of top-hat like lasers with frequencies ω 1, ω 2 and wave numbers k 1, k 2 in pre-formed rippled density (corrugated) plasma is proposed. In this mechanism, intensity variation of lasers offers nonlinear ponderomotive force at frequency ω ′ = ω 1 - ω 2 and wave number k ′ = k 1 - k 2 which couples with density ripples in the plasma and leads to a strong nonlinear oscillatory current that resonantly excites highly focused and intense THz radiation at frequency ω U H = √(ωp2 + ωc2) (where ω c is electron cyclotron frequency). The efficiency of emitted THz radiation of the order of 15% is obtained under optimum conditions. It is observed that focus and intensity of emitted radiation can be controlled by selecting a proper profile index of the lasers, ripple parameters, and tuning of external magnetic field. © 2014 AIP Publishing LLC. Source

Varshney P.,Jaypee Institute of Information Technology | Sajal V.,Jaypee Institute of Information Technology | Singh K.P.,Singh Simutech Pvt. Ltd. | Kumar R.,Jaypee Institute of Information Technology | Sharma N.K.,Jaypee Institute of Information Technology
Journal of Applied Physics | Year: 2015

A scheme of terahertz (THz) radiation generation is investigated by photo-mixing of two super Gaussian laser beams having different frequencies (ω1, ω2) and wave numbers (k→1, k→2) in a performed corrugated plasma embedded with transverse dc magnetic field. Lasers exert a nonlinear ponderomotive force, imparting an oscillatory velocity to plasma electrons that couples with the density corrugations (n' = nα0eiαz) to generate a strong transient nonlinear current, that resonantly derives THz radiation of frequency ∼ωh (upper hybrid frequency). The periodicity of density corrugations is suitably chosen to transfer maximum momentum from lasers to THz radiation at phase matching conditions ω = ω1 - ω2 and k → = k→1 - k→2 + α→. The efficiency, power, beam quality, and tunability of the present scheme exhibit high dependency upon the applied transverse dc magnetic field along with q-indices and beam width parameters (a 0) of super Gaussian lasers. In the present scheme, efficiency ∼10-2 is achieved with the optimization of all these parameters. © 2015 AIP Publishing LLC. Source

Singh K.P.,University of Sydney | Singh K.P.,Singh Simutech Pvt. Ltd. | Kumar M.,Singh Simutech Pvt. Ltd.
Journal of Physical Chemistry C | Year: 2011

We have simulated ion current rectification (ICR) in a bipolar nanochannel fluidic diode for different nanochannel diameters, electrolyte concentrations, and surface charge densities. The ICR decreases with diameter of the fluidic nanochannel due to decrease in unipolar character of the electrolyte. The ICR decreases with electrolyte concentration due to surface charge screening by counterions. The ICR increases with channel diameter for a given ratio of channel diameter to Debye length. Scaling of forward and reverse current densities with electrolyte concentration has been determined using curve fitting for different values of surface charge densities and channel diameters. The ICR can be increased by increasing surface charge density to enhance unipolar character of the electrolyte. The fluid velocity close to the nanochannel walls is driven by body force and along the center by the fluid pressure, which gives rise to a curly fluid flow. © 2011 American Chemical Society. Source

Singh K.P.,University of Sydney | Singh K.P.,Singh Simutech Pvt. Ltd. | Kumar M.,Singh Simutech Pvt. Ltd.
Physical Review Special Topics - Accelerators and Beams | Year: 2011

The acceleration of electrons by a radially polarized intense laser pulse has been studied. The axial electric field of the laser is responsible for electron acceleration. The axial electric field increases with decreasing laser spot size; however, the laser pulse gets defocused sooner for smaller values and the electrons do not experience high electric field for long, reducing the energy they can reach. The electron remains confined in the electric field of the laser for longer and the electron energy peaks for the normalized laser spot size nearly equal to the normalized laser intensity parameter. Electron energy peaks for initial laser phase φ0=π due to accelerating laser phase and decreases with transverse initial position of the electrons. The energy and angle of the emittance spectrum of the electrons generated during ionization of krypton and argon at low densities have been obtained and a right choice of laser parameters has been suggested to obtain high energy quasimonoenergetic collimated electron beams. It has been found that argon is more suitable than krypton to obtain high energy electron beams due to higher ionization potential of inner shells for the former. © 2011 American Physical Society. Source

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