Rinku Sharma

Effect of relativistic and ponderomotive nonlinearities on stimulated Raman scattering in laser plasma interaction

In this paper, the authors have investigated the effect of ultra-intense laser beam filaments on stimulated Raman scattering (SRS) in unmagnetized plasma when relativistic and ponderomotive nonlinearities are operative. First, the filamentary dynamics of laser beam is studied. In these structures, the plasma wave generation and associated SRS process are studied. The effect of filamentation on SRS back reflectivity has been studied in detail. For the typical laser plasma parameters, i.e., laser beam Nd:YAG (λ=1064nm), laser beam radius=15μm, laser power flux=6×1017W∕cm2, electron density=1.9×1019percm3, the SRS reflectivity reduces by a factor 2.5 due to ponderomotive effects.

Collision Strengths from Ground Levels of Fe XVII by Including Relativistic Term Coupling Effects

The R-matrix method is used to calculate collision strengths from ground state to the first 26 fine-structure levels of Fe XVII by including the relativistic term coupling coefficients in the semi-Breit-Pauli approximation. Configuration interaction wave functions are used to represent the 15 lowest LS-coupled target states in the R-matrix expansion. Results obtained are compared with the other distorted wave calculations.

Rotational transitions in the presence of a laser field

A semi-classical theory of multiphoton rotational excitations by ionic collisions is developed. The rotational field surfaces are determined via a quasi-energy method. Transitions among the dressed quasi-energies are studied using a diagonalization technique. Some new results are obtained for state to state rotationally inelastic cross-sections, and their behaviour with change of laser parameters is discussed.

Modeling the effect of doping on the catalyst-assisted growth and field emission properties of plasma-grown graphene sheet

A theoretical model describing the effect of doping on the plasma-assisted catalytic growth of graphene sheet has been developed. The model accounts the charging rate of the graphene sheet, kinetics of all the plasma species, including the doping species, and the growth rate of graphene nuclei and graphene sheet due to surface diffusion, and accretion of ions on the catalyst nanoparticle. Using the model, it is observed that nitrogen and boron doping can strongly influence the growth and field emission properties of the graphene sheet. The results of the present investigation indicate that nitrogen doping results in reduced thickness and shortened height of the graphene sheet; however, boron doping increases the thickness and height of the graphene sheet. The time evolutions of the charge on the graphene sheet and hydrocarbon number density for nitrogen and boron doped graphene sheet have also been examined. The field emission properties of the graphene sheet have been proposed on the basis of the results obtained. It is concluded that nitrogen doped graphene sheet exhibits better field emission characteristics as compared to undoped and boron doped graphene sheet. The results of the present investigation are consistent with the existing experimental observations.

Generating tunable THz radiation using rippled density plasma driven by density modulated relativistic electron beam

The generation of Terahertz (THz) radiation by a density modulated relativistic electron beam (REB) using rippled density plasma, oriented at a suitable angle along the direction of radiation wave, is being investigated in this paper. The non-linear interaction of density modulated REB with ripple density plasma modifies the dispersion relation of the radiation wave co-propagating with the beam wave. Using fluid equations model, it is found that the requisite ripple wavelength decreases as the ripple angle increases and becomes steeper for resonant THz radiation emission. Thus, the radiation wavelength in terahertz range can be tuned by varying the ripple wavelength and beam energy. In addition, it is investigated that the growth rate of THz radiation emission scales as the one-third power of beam current, two-third power of ripple plasma density, and one-third power of modulation index. The output power and efficiency of THz radiation emission depend on the modulation index and reach the largest value wh...

Photoionization of ground and excited states of neon like K X

The close-coupling R-matrix method is used to calculate cross-sections for photoionization of K X from its ground and first three excited states. Configuration interaction wave-functions are used to represent two target states of K X I retained in the R-matrix expansion. The positions and effective quantum numbers for the Rydberg series converging to the excited state 2s2p6 2Se of the residual ion, are predicted.

Laser assisted electron-alkali atom collisions

Lasar assisted inelastic scattering of electrons by alkali atoms is studied theoretically. The non-perturbative quasi-energy method, which is generalised for many atomic states, is used to describe the laser–atom interaction, and the electron–atom interaction is treated within the first Born approximation. We have calculated the total cross section for the excitation of sodium atoms due to simultaneous electron–photon collisions. We show the effect of laser and collision parameters, e.g. laser intensity, polarisation and incident electron energy, on the excitation process.

Coherent terahertz radiation from beam-driven upper hybrid wave in magnetostatic plasma

ABSTRACT A scheme for generating tunable terahertz radiation using relativistic electron beam-induced upper hybrid wave immersed in a magnetized plasma is investigated. The ponderomotive force applied to the beam electrons because of electromagnetic radiation wave and pump wave generates the non-linear current density in the high-frequency regime. For an appropriate pump wave frequency, under the condition of phase matching the THz radiation wave is obtained. The enhancement in the radiation power occurs along the axial direction in the vicinity of Cerenkov resonance. Our analytical expression shows that the growth rate in the unstable modes of the THz radiation wave increases with beam density (beam current) and the modulation index. In addition, the growth rate of the instability decreases with an increase in radiation wave frequency and scales as the inverse cube root of radiation frequency. An interesting result obtained from our model is that an increase in cyclotron frequency causes the growth decrement in THz radiation emission, while the efficiency of THz radiation emission increases with the growth rate and the modulation index. Also, the emission of the THz radiation wave becomes larger as the modulation index approaches unity.

Signal processing of Raman signatures and realtime identification of hazardous molecules using continuous wavelet transformation (CWT)

Continuous use of explosives by terrorists throughout the world has led to the great necessity in explosives detection technology, especially in technologies that have potential for stand-off detection. The Raman vibrational spectrum of molecules provides an excellent fingerprint for species identification. Analysis of Raman signatures manually is time-consuming and cannot be afford by security personal in real scenario. Automation of detection, acquisition and analysis of Raman signal is required for operations in real scenario. In this work, we have developed software which caters all these process automatically and finally mentions name of material under observation for standoff detection. This is based on continuous wavelet transformation (CWT). This algorithm/ software is capable of identifications/ discrimination of very similar chemicals like trinitrobenzene (TNB), trinitrotoluene (TNT) and dinitrotoluene (DNT).

Effect of doping on growth and field emission properties of spherical carbon nanotube tip placed over cylindrical surface

Theoretical investigations to study the effect of doping of hetero-atoms on the growth and field emission properties of Carbon Nanotubes (CNTs) tip placed over a cylindrical surface in complex plasma have been carried out. A theoretical model incorporating kinetics of plasma species such as electron, ions, and neutral atoms including doping elements like nitrogen (N) and boron (B) and energy balance of CNTs in a complex plasma has been developed. The effect of doping elements of N and B on the growth of CNTs, namely, the tip radius has been carried out for typical glow discharge plasma parameters. It is found that N and B as doping elements affect the radius of CNTs extensively. We obtain small radii of CNT doped with N and large radius of CNT doped with B. The field emission characteristics from CNTs have therefore been suggested on the basis of results obtained. Some of theoretical results are in compliance with the existing experimental observations.