Sixth-order Dispersion Research Articles

Dispersion Engineered Capillary-Assisted Chalcogenide Optical Fiber Based Mid-IR Parametric Sources

We report the detailed theoretical investigations of a capillary-assisted chalcogenide optical fibers exhibiting three zero dispersion wavelengths and small magnitude of chromatic dispersion. The dispersion characteristics of the proposed fiber can be tailored externally by temperature when the air-capillary is infiltrated with suitable thermooptic liquids. This has led to design and development of thermally tunable broadband CW pumped optical parametric amplifier (OPA) in mid-IR region with bandwidth greater than 2000 nm. By considering the sixth-order dispersion parameter in the phase-matching condition, we have shown the temperature-dependent various phase-matching topologies which are only possible with different fiber structures as reported earlier. The key benefits of the proposed tunable OPA are the generation of new radiations of varying line widths.

Continuous-wave pumped, tunable mid-infrared fiber-optic parametric sources

In this paper, we investigate the effect of sixth-order dispersion parameter on the parametric amplification characteristics of a specially designed capillary-assisted chalcogenide core (As2S3) and silica-clad step-index optical fiber. The micro-sized capillary in the core of the fiber is filled with thermoresponsive liquid that gives rise to tunable parametric gain in a 50 cm long fiber and generation of varying linewidth non-Cherenkov radiations from near-IR to mid-IR when a 3 μm cw pump is used. It is observed that the sixth-order dispersion plays a crucial role in the creation of new sidebands.

Dispersion relation and growth rate for a corrugated channel free-electron laser with a helical wiggler pump

The effects of corrugated ion channels on electron trajectories and spatial growth rate for a free-electron laser with a one-dimensional helical wiggler have been investigated. Analysis of the steady-state electron trajectories is performed by solving the equations of motion. Our results show that the presence of a corrugated channel shifts the resonance frequency to smaller values of ion channel frequency. The sixth-order dispersion equation describing the coupling between the electrostatic beam mode and the electromagnetic mode has also been derived. The dispersion relation characteristic is analyzed in detail by numerical solution. Results show that the growth rate of instability in the presence of corrugated ion channels can be greatly enhanced relative to the case of an uniform ion channel.

Robustness Optimization of Fiber Index Profiles for Optical Parametric Amplifiers

Optical fibers with index profiles that are optimized for broadband double pumped parametric amplifiers are thoroughly investigated. The analysis includes random variations in the radii of the profile along the fiber length (introduced in the fabrication process). By optimizing the fourth order dispersion parameter and the effective area we obtain fiber designs that provide flat spectral gain over 200 nm with 3.5 W pump lasers and, at the same time, have robust operation wavelength against fluctuations of up to 1% in the radii of the index profile. These fibers show positive and very small fourth order dispersion. Our results indicate that in such low dispersion fibers, the sixth order dispersion parameter must be considered in the optimization algorithm.

Possible Role of MHD Waves in Heating the Solar Corona

Heating of the solar corona by MHD waves has been investigated. Taking account of dissipation mechanisms self-consistently, a new general dispersion relation has been derived for waves propagating in a homogeneous plasma. Solution of this sixth-order dispersion relation provides information on how the damping of both slow and fast mode waves depends upon the plasma density, temperature, field strength, and angle of propagation relative to the background magnetic field. Wave quantities with and without dissipation are presented. In particular, we consider one of the most important clues from space observations that viscosity of coronal plasma may be orders of magnitude different from its classical value in heating of the corona by MHD waves.

亜音速非平衡ディスク形MHD発電機における

The behavior of magneto-acoustic waves in a nonequilibrium subsonic disk MHD generator was examined. The solution of the sixth-order dispersion relation obtained by linearizing the set of MHD equations suggested that a magneto-acoustic wave which propagates at a velocity of ur − a(ur: radial fluid velocity, a: sound velocity) should be damped in subsonic flow. From time-dependent quasi-one-dimensional simulations, it was verified that the pressure disturbance in the subsonic generator was damped at approximately the same rate as the value predicted by the linear theory. From a simplified analytical model, the mechanism of magneto-acoustic instability with fully ionized seed was discussed, and the damping criterion for the magneto-acoustic wave was clarified. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 142(4): 20–26, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.10108

The possible role of MHD waves in heating the solar corona

The possible role of waves in the heating of the solar corona has been investigated. A general dispersion relation has been derived for waves propagating in a homogeneous plasma subject to dissipation by viscosity and thermal conduction. The dissipation mechanisms have been incorporated self-consistently into the equations, and no assumptions about the strength of the damping have been made. Solutions of the sixth-order dispersion relation provide information on how the damping of both slow and fast mode waves depends upon the plasma density, temperature, field strength, and angle of propagation relative to the background magnetic field. We provide a detailed comparison to the standard approach, which is to solve for the wave quantities in the absence of dissipation and then to use these quantities in expressions for the heating due to viscosity and thermal conduction.

Electromagnetic instability and emission from counterpropagating Langmuir waves

This paper analyzes fundamental electromagnetic (em) emission, near the plasma frequency, from a pair of counterpropagating Langmuir pump waves in an externally driven plasma. The emission is a result of parametric instabilities of both Stokes (frequency-downshifted) and anti-Stokes (frequency-upshifted) em waves. A new, sixth-order dispersion relation is derived for the linearly unstable em waves. Previous treatments of this problem neglected the existence of two independent density ‘‘gratings’’ produced by the beating together of high-frequency waves. These gratings, which can be resonant ion-acoustic waves, are of comparable importance, and must be considered together in order to give the correct growth rates. The present results may have relevance to fundamental emission from laser-driven targets and to other systems, such as the radio-wave-modified ionosphere.