Generation of Efficient Terahertz Radiation by Relativistic Self-Focusing of A Cosh-Gaussian Laser Beam in A Magnetized Plasma

This paper presents a scheme for the generation of terahertz (THz) radiation by self-focusing of a cosh-Gaussian laser beam in the magnetized and rippled density plasma, when relativistic nonlinearity is operative. The strong coupling between self-focused laser beam and pre-existing density ripple produces nonlinear current that originates THz radiation. THz radiation is produced by the interaction of the cosh-Gaussian laser beam with electron plasma wave under the appropriate phase matching conditions. Expressions for the beamwidth parameter of cosh-Gaussian laser beam and the electric vector of the THz radiation have been obtained using higher-order paraxial theory and solved numerically. The self-focusing of the cosh-Gaussian laser beam and its effect on the generated THz amplitude have been studied for specific laser and plasma parameters. Numerical study has been performed on various values of the decentered parameter, incident laser intensity, magnetic field, and relative density. The results have also been compared with the paraxial region as well as the Gaussian profile of laser beam. Numerical results suggest that the self-focusing of the cosh-Gaussian laser beam and the amplitude of THz radiation increase in the extended paraxial region compared to the paraxial region. It is also observed that the focusing of the cosh-Gaussian laser beam in the magnetized plasma and the amplitude of the THz radiation increases at higher values of the decentered parameter.

Improvement in Sintered Tungsten Carbide Tool Surface Integrity Using Femtosecond Pulse Laser

In this paper, we propose a surface integrity technique referred to as pulse laser grinding (PLG). This method is a combination of laser ablation and averaging processes, such as grinding, and has two characteristic features. The first feature is that the irradiation area consists of a long-focus lens and a pulse laser with a Gaussian profile, and this method has a laser irradiation area equivalent to that of the grinding wheel. However, owing to the difference in the removal process of PLG and that of conventional grinding, the surface roughness after processing is expected to be different. The second feature is that the workpiece is placed at an approximately parallel angle between the laser axis and the work surface to undergo laser ablation on the surface. The characteristic piece placement restrains laser-specific problems such as debris and redeposition. This study targets sintered tungsten carbide (WC-Co), for which it is particularly difficult to form low-roughness surfaces. Binder removal followed by WC grain detachment caused by conventional grinding contributes to the increase in roughness and deterioration of corner sharpness. The experimental results of PLG with a sufficiently averaged surface of a WC-Co tool confirmed that the parallel roughness reached an arithmetical mean roughness (Ra) of 0.025 μm, and the perpendicular roughness reached Ra below 0.006 μm, in agreement with the aforementioned considerations.

The spectral line asymmetry of the Doppler effect in relativistic plasmas

{In this work, we present a comparative study between the relativistic and non- relativistic Doppler effects on spectral line profiles in ultra-hot plasmas at the laboratory system. We have established an exact formula of the relativistic Doppler profile in ultra-high-temperature plasma that is not a Gaussian one (unlike the nonrelativistic Doppler profile that is Gaussian). We have also derived a new FWHM (Full Width at Half Maximum) formula of the corresponding profile that is different from the non-relativistic FWHM (sqrtlog(T=M)). We have also shown that, in the relativistic case, Doppler broadening exhibits an asymmetry of spectral line profile (non- gaussian profile). To ensure the validity of our investigation, we have compared our theoretical calculation with the experimental results that shows a good agreement.

An Investigation of the Effect of Intermetallic Compounds on the Mechanical and Electrical Properties of Friction Stir Welded Al and Cu Busbar for Battery Pack Applications

Aluminium and copper (Al-Cu) busbar is widely used as a core component in Lithium-Ion (Li-ion) batteries. The Al-Cu busbar is challenging to fabricate with the traditional welding processes because of its high thermal conductivity. In the present study, the Al-Cu busbar is fabricated using the friction stir welding method. The effect of temperature and vibration generated during the welding process on the formation of intermetallic compounds (IMCs) is studied by using the effective formation model and found that Al2Cu is the first to form at the interface. The IMC formation at the joint interface had both detrimental (Al-rich IMC) and beneficial (Cu-rich IMC) effects. The presence of detrimental IMCs affects the joint strength of about 36 % as compared to the sample with the highest tensile load. The surface electrical conductivity is measured by using a Gaussian profile method and found in the range of 0.94 – 5.37 μ Ω·mm. The welded samples with the presence of Al2Cu3 and Al4Cu9 IMC at the interface are found to have higher electrical conductivity. Interestingly, the sample with a higher tensile load had observed higher electrical conductivity due to the formation of Cu-rich IMC, i.e., Al4Cu9.

The suite of Taylor–Galerkin class schemes for ice transport on sphere implemented by the INMOST package

Realizations of the numerical solution of the scalar transport equation on the sphere, written in divergent form, are presented. Various temporal discretizations are considered: the one-step Taylor–Galerkin method (TG2), the two-step Taylor–Galerkin method of the second (TTG2), third (TTG3), and fourth (TTG4) orders. The standard Finite-Element Galerkin method with linear basis functions on a triangle is applied as spatial discretization. The flux correction technique (FCT) is implemented. Test runs are carried out with different initial profiles: a function from C ∞ (Gaussian profile) and a discontinuous function (slotted cylinder). The profiles are advected by reversible, nondivergent velocity fields, therefore the initial distribution coincides with the final one. The case of a divergent velocity field is also considered to test the conservation and positivity properties of the schemes. It is demonstrated that TG2, TTG3, and TTG4 schemes with FCT applied give the best result for small Courant numbers, and TTG2, TTG4 are preferable in case of large Courant number. However, TTG2+FCT scheme has the worst stability. The use of FCT increases the integral errors, but ensures that the solution is positive with high accuracy. The implemented schemes are included in the dynamic core of a new sea ice model developed using the INMOST package. The acceleration of the parallel program and solution convergence with spatial resolution are demonstrated.

Generation of High-Order Vortex States From Two-Mode Squeezed States

We report a scheme for generation of high-order quadrature vortex states using two-mode photon-number squeezed states, generated via the non-linear process of Spontaneous Parametric Down Conversion. By applying a parametric rotation in the quadratures (X^,Y^), using a ϕ converter, the Gaussian profile of the photon-number squeezed input state can be mapped into a superposition of Laguerre-Gauss modes in the quadratures with N vortices or singularities, for an input state containing 2N photons, thus mapping photon-number fluctuations to interference effects in the quadratures. Our scheme has the potential to improve measurement sensitivity beyond the Standard uantum Limit (SQL ∝N), by exploiting the advantages of optical vortices, such as high dimensionality or topological properties, for applications requiring reduced uncertainty, such as quantum cryptography, quantum metrology and sensing.