Mohammad F. Mahmood

Singular solitons in optical metamaterials by ansatz method and simplest equation approach

This paper derives singular 1-soliton solution for optical metamaterials. There are two integration approaches that obtains the solution. These are the ansatz approach and the simplest equation approach. The second method also leads to an additional set of solutions that emerge as a by-product. These are topological soliton, rational solution and singular periodic solution. The constraint conditions for the existence of these solutions are also exhibited. The numerical simulation of a topological 1-soliton solution is also exhibited.

Optical solitons in nonlinear directional couplers with spatio-temporal dispersion

This paper addresses solitons in nonlinear directional couplers in non-Kerr law media, with spatio-temporal dispersion. Both twin-core couplers as well as multiple-core couplers are studied. The nonlinearities studied are Kerr law, power law, parabolic law, dual-power law and log law. Bright, dark and singular soliton solutions of the governing equation are studied.

OPTICAL SOLITON PERTURBATION IN NANOFIBERS WITH IMPROVED NONLINEAR SCHRÖDINGER'S EQUATION BY SEMI-INVERSE VARIATIONAL PRINCIPLE

This paper studies the perturbation of the improved version of the nonlinear Schrodingers equation that governs the propagation of solitons through nonlinear optical fibers. The semi-inverse variational principle is employed in order to obtain an analytical soliton solution in presence of the perturbation terms. There are three types of nonlinearity that will be studied. They are Kerr law, power law and the log law. The constraint conditions will naturally fall out in order for the soliton solutions to exist. The numerical simulations supplement the analytical results for each of the three laws of nonlinearity.

Raman solitons in nanoscale optical waveguides, with metamaterials, having polynomial law non-linearity

This paper reports bright Raman soliton solutions in optical metamaterials. The polynomial law and triple law non-linearity are discussed. Travelling wave hypothesis is employed to conduct the mathematical analysis. Implicit solutions in terms of elliptic integral of the third kind are obtained. The analytical results are supplemented with numerical simulations.

Opacity and conductivity measurements in noble gases at conditions of planetary and stellar interiors

Significance Planets and stars contain matter at extreme pressures and temperatures hidden deep beneath their opaque surfaces. Unable to see these states of matter directly, we instead produce them in laboratory experiments. Here a novel method of studying extreme states in a tabletop experiment is described and applied to common planet- and star-forming materials, the noble gases. Helium, neon, argon, and xenon transform in the experiments from transparent electrical insulators to opaque electrical conductors. In Saturn, rain composed of noble gas becomes conductive as it falls and can form a protective layer around the planetary core that prevents the core from dissolving into surrounding metallic hydrogen. White dwarf stars have unexpectedly opaque helium atmospheres, causing them to age slower than anticipated. The noble gases are elements of broad importance across science and technology and are primary constituents of planetary and stellar atmospheres, where they segregate into droplets or layers that affect the thermal, chemical, and structural evolution of their host body. We have measured the optical properties of noble gases at relevant high pressures and temperatures in the laser-heated diamond anvil cell, observing insulator-to-conductor transformations in dense helium, neon, argon, and xenon at 4,000–15,000 K and pressures of 15–52 GPa. The thermal activation and frequency dependence of conduction reveal an optical character dominated by electrons of low mobility, as in an amorphous semiconductor or poor metal, rather than free electrons as is often assumed for such wide band gap insulators at high temperatures. White dwarf stars having helium outer atmospheres cool slower and may have different color than if atmospheric opacity were controlled by free electrons. Helium rain in Jupiter and Saturn becomes conducting at conditions well correlated with its increased solubility in metallic hydrogen, whereas a deep layer of insulating neon may inhibit core erosion in Saturn.

Optical Gaussons in nonlinear directional couplers

Abstract This paper studies optical Gaussons in nonlinear directional couplers. Both twin-core couplers as well as multiple-core couplers are considered. For multiple-core couplers, coupling with nearest neighbors as well as coupling with all neighbors are considered. A closed form optical Gausson solution is obtained in all of these cases where the amplitude of the Gaussons is governed by a nonlinear difference equation. The domain restrictions naturally fall out as constraint conditions in order for the Gaussons to exist.

Structural and chemical properties of the nitrogen-rich energetic material triaminoguanidinium 1-methyl-5-nitriminotetrazolate under pressure.

The structural and chemical properties of the bi-molecular, hydrogen-bonded, nitrogen-rich energetic material triaminoguanidinium 1-methyl-5-nitriminotetrazolate C(3)H(12)N(12)O(2) (TAG-MNT) have been investigated at room pressure and under high pressure isothermal compression using powder x-ray diffraction and Raman and infrared spectroscopy. A stiffening of the equation of state and concomitant structural relaxation between 6 and 14 GPa are found to correlate with Raman mode disappearances, frequency discontinuities, and changes in the pressure dependence of modes. These observations manifest the occurrence of a reversible martensitic structural transformation to a new crystalline phase. The onset and vanishing of Fermi resonance in the nitrimine group correlate with the stiffening of the equation of state and phase transition, suggesting a possible connection between these phenomena. Beyond 15 GPa, pressure induces irreversible chemical reactions, culminating in the formation of a polymeric phase by 60 GPa.

Bright and exotic solitons in optical metamaterials by semi-inverse variational principle

This paper addresses solitons in optical metamaterials. The semi-inverse variational principle (SVP) is utilized to secure bright soliton solutions to the governing model. There are five forms of nonlinearity that are studied in this paper. They are Kerr law, power law, parabolic law, dual-power law and finally the log law nonlinearity. In particular for Kerr law nonlinearity, there are two additional forms of soliton solutions obtained. They are cosh-Gaussian pulses and bright-dark combo solitons and these are collectively being referred to as exotic solitons. There are several constraint conditions that naturally emerge for these solitons to exist.

Coherent Super Continuum Generation in Photonic Crystal Fibers at Visible and Near Infrared Wavelengths

Physical mechanisms those interplay in generating super continuum from femto-second pulses propagated through photonic crystal fiber (PCF) have been investigated here. We compare spectrums from two distinct PCFs with different group velocity dispersion profiles to determine the most desirable spectral features such as stronger and ripple free output spectra at wavelength regions of interest, specifically around near infrared wavelength which we can use for coherent anti-Stokes Raman Scattering microscopy of lipid-rich structures. Coherency of the pulses from these two PCFs was also compared. The spectrums from theoretical model will provide us guidance for future experiments.

Optical solitons in nonlinear directional couplers with G′/G-expansion scheme

This paper obtains soliton solutions in optical couplers. The governing equation is solved by the aid of G′/G-expansion scheme. There are four types of nonlinear media that are taken into consideration. These are Kerr law, power law, parabolic law, and dual-power law. There are two kinds optical couplers studied in this paper. They are twin-core couplers and multiple-core couplers, where coupling with nearest neighbors as well as coupling with all neighbors are considered. Dark and singular soliton solutions are retrieved. These soliton solutions come with constraint conditions that must hold for the solitons to exist.