Propagation Properties Of Pulses Research Articles

Influence of wind-roughed sea surface on detection performance of spaceborne oceanic lidar

The wind-roughed sea surface influences the propagation properties of the laser beam and consequently affects the detection accuracy of spaceborne oceanic lidar. A comprehensive analysis of this problem is lacking to date. Herein, the Cox and Munk surface model is applied to the spaceborne oceanic lidar radiative transfer emulator to solve this problem. The effects of wind-roughed sea surface on oceanic lidar laser pulse propagation properties, such as the deflection angle of the direction, the inaccuracy of the signal depth, and the recommended incident angles, are studied using this model. The relationships among the wind speed, the incident angle and the propagation properties of the laser beam when passing through the sea surface are established. The maximum possible error of detection depth is within 8.2% when the wind speed is below 15 m/s and the incident zenith angle is less than 30°. And it can be reduced to 1.8% by profile averaging, which reveals the spaceborne oceanic lidar is capable to detect the global ocean profile information effectively in windy conditions. Moreover, the recommended incident angles for an oceanic lidar system are 37° and 35°, when the effective reflectance of the whitecaps are 0.2 and 0.6, respectively. The conclusions of this paper have reference value for oceanic lidar remote sensing in practice.

Spatio-temporal properties of pulse propagation in a graphene quantum system

In this paper we have theoretically studied the spatial-temporal evolution of electromagnetic light propagation through a four-level graphene quantum system by using density matrix method and perturbation theory. The four-level graphene quantum medium interacted by an elliptical polarized coupling and a weak probe lights, respectively. We present the analytical solution for solving the Maxwell–Bloch equations for graphene and electromagnetic field in space and time domains. Then, we have analyzed the dynamic control of pulse propagation and optical dual switching in such a laser-driven quantum system. Our theoretical findings show that by adjusting the optical parameters such as elliptical angle i.e. phase difference between right-and-left circularly polarized, one can easily control the absorption spectrum and pulse propagation of the probe light in graphene medium. Our results may have potential applications in designing the new quantum devices for usage in quantum information processing.

Long wavelength superluminal pulse propagation in a defect slab doped with GaAs/AlGaAs multiple quantum well nanostructure

In this paper, long wavelength superluminal and subluminal properties of pulse propagation in a defect slab medium doped with four-level GaAs/AlGaAs multiple quantum wells (MQWs) with 15 periods of 17.5 nm GaAs wells and 15 nm [Formula: see text] barriers is theoretically discussed. It is shown that exciton spin relaxation (ESR) between excitonic states in MQWs can be used for controlling the superluminal and subluminal light transmissions and reflections at different wavelengths. We also show that reflection and transmission coefficients depend on the thickness of the slab for the resonance and nonresonance conditions. Moreover, we found that the ESR for nonresonance condition lead to superluminal light transmission and subluminal light reflection.

Topology bifurcation of a magnetic flux surface in toroidal plasmas

The bifurcation of magnetic topology is identified by a significant change in the heat pulse propagation properties in magnetized plasmas. Clear evidence of stochastization of the magnetic surfaces near a rational surface is observed in the core plasma with weak magnetic shear in the Large Helical Device by slowly decreasing the magnetic shear and measured by applying heat pulses driven by modulated electron cyclotron heating (MECH). Three topologies of the magnetic flux surfaces (a nested magnetic island and partial and full stochastization) are identified by the patterns of heat pulse propagation observed in the flat temperature region in the plasma. Slow heat pulse propagation exhibiting a non-monotonically increasing delay time is evidence of a magnetic island, while the fast heat pulse propagation observed in the plasma with medium magnetic shear is evidence of the stochastization of the magnetic surfaces. The region with the fast heat pulse propagation varies with a slight change of magnetic shear. There are two types of stochastization of the magnetic surfaces. In one, the stochastization region is localized near the rational surface (partial stochastization) and in the other, the region is extended to the magnetic axis (full stochastization). The appearance of a stochastic magnetic field is not caused by MHD instability. The significant increase of the ratio of electron thermal diffusivity to ion thermal diffusivity is consistent with that expected by stochastization of the magnetic field.

COUPLED NONLINEAR TRANSMISSION LINES FOR DOUBLING REPETITION RATE OF INCIDENT PULSE STREAMS

We investigated the properties of pulse propagation on coupled nonlinear transmission lines to develop a method for doubling repetition rate of incident pulse streams. Coupled nonlinear transmission lines are two transmission lines with regularly spaced Schottky varactors coupled with each other. It is found that both of the modes developed in a coupled line can support soliton-like pulses because of Schottky varactors. We discuss the fundamental properties of each soliton-like pulse, including the width and velocity, and propose a method of doubling repetition rate of incident pulse streams by managing these soliton-like pulses.

Nonlinear traveling-wave field effect transistors for amplification of short electrical pulses

We investigated the properties of pulse propagation on nonlinear traveling-wave field effect transistors (TW-FET) to develop a method for amplifying short electrical pulses. TW-FETs are a special type of FET whose electrodes are employed not only as electrical contacts but also as transmission lines. Due to the presence of electromagnetic couplings between the gate and drain lines, two different propagation modes called the c mode and π mode are developed on a TW-FET. Moreover, the Schottky contact beneath the gate electrode creates an ideal source of nonlinearity for soliton-like propagation. We can design the TW-FET to amplify only soliton-like pulses carried by one of the two modes and attenuate the ones carried by the other mode. This paper discusses the fundamental properties of a nonlinear TW-FET, including the width and velocity of a soliton-like pulse carried by c and π modes, and gives design criteria of amplification of soliton-like pulses.

Generation of short electrical pulses using nonlinear traveling-wave field effect transistors

We investigated the properties of pulse propagation on nonlinear traveling-wave field effect transistors (TWFET) in order to develop a method for generating short electrical pulses. We considered the case where a decreasing voltage pulse is applied to the gate line and an increasing one is simultaneously applied to the drain line. By properly designing the top and bottom levels of the applied pulses, every FET simulates an electronic switch (the switch is open for voltages greater than some fixed threshold, and closed otherwise). On a line with such switches, a pulse experiences great shortening by the development of steep exponential wave; therefore, a TWFET operates as a short pulse generator.

Pulse propagation in decorated granular chains: An analytical approach

We study pulse propagation in one-dimensional chains of spherical granules decorated with small grains placed between large granules. The effect of the small granules can be captured by replacing the decorated chains by undecorated chains of large granules of appropriately renormalized mass and effective interaction between the large granules. This allows us to obtain simple analytic expressions for the pulse propagation properties using a generalization of the binary collision approximation introduced in our earlier work [Phys. Rev. E 80, 031303 (2009); Phys. Rev. E 69, 037601 (2004)].

Onset of unidirectional pulse propagation in an excitable medium with asymmetric heterogeneity

Heterogeneity is one of the most important and ubiquitous types of external perturbations in dissipative systems. To know the behaviors of pulse waves in such media is closely related to studying the collision process between the pulse and the heterogeneity-induced-ordered pattern. In particular, we focus on unidirectional propagation of pulses in a medium with an asymmetric bump heterogeneity. This topic has attracted much interest recently with respect to potential computational aspects of chemical pulse propagation as well as with respect to pulse propagation in biological signal processing. We employ a three-component reaction-diffusion system with one activator and two inhibitor species to illustrate these issues. The reduced dynamics near a drift bifurcation describes the phenomena in the full partial differential equations by ordinary differential equations. Such a reduced dynamics is able to capture unidirectional propagation properties of pulses near an asymmetric heterogeneity in a qualitatively correct way. A remarkable feature is that such unidirectional behavior is linked to the imperfection of global bifurcation structure and the resulting asymmetric locations of critical points.

Subluminal and Superluminal Phenomena in a Four-Level Atom

In a four-level atomic system, we investigate the light pulse propagation properties interacting with only one laser field. It is shown that in the steady state, the group velocity of the light pulse can be changed from subluminal to superluminal by varying the field detuning. Meanwhile, the effects of the field intensity on the group velocity are also shown. At last, with special parameters, the analytical solution for the group index is also obtained.

Upper level and phase controlling group velocity in V-type system

With the external field coupling the two upper levels, we investigate the light pulse propagation properties with weak probe field in a V-type system. Due to the external upper level (UL) coupling field, the dispersion of the system has been influenced by the relative phase. It is shown that the UL field and the relative phase can be regarded as switches to manipulate light propagation between subluminal and superluminal. (c) 2007 Elsevier B.V. All rights reserved.

Stability and transient effects in nanosecond ultraviolet light filaments in air

We investigate the transient behavior and stability of nanosecond duration ultraviolet pulses propagating in air. Both the transient behavior arising from the finite pulse duration and the modulational instability, are found to cause pulses to fragment over lengths on the scale of meters. We discuss the theoretical and experimental implications of the instability and transient effects for long duration pulse propagating in air and generating filaments. In particular, our results imply that continuous-wave models are very limited when used to predict dynamical properties of pulse propagation.

A VARIATIONAL APPROACH IN THE DISSIPATIVE CUBIC-QUINTIC NONLINEAR SCHRÖDINGER EQUATION

The properties of pulse propagation in a nonlinear fiber including a linear damped term added in the nonlinear Schrödinger equation with cubic and quintic terms is analyzed analytically. We apply the variational modified approach based on the Lagrangian that describes the dynamic of a system and, with a suitable trial function, we obtain a solution which is as accurate as a pertubative solution found by inverse scattering transformation in earlier works. As a result, we show that the quintic term can retain the pulse propagation more stably and in a greater time in optical fiber.

Soliton-like pulses governed by fourth order dispersion in optical fibers

The properties of pulse propagation in a nonlinear fiber including negative fourth order dispersion added to anomalous second order dispersion are analyzed numerically and analytically. An exact localized analytical solution is presented, and using an approximate variational method, an entire family of stationary approximate solutions is also obtained. These solutions are found to be in excellent agreement with numerical simulations.

Asymptotic propagation properties of pulses in a soliton-based optical-fiber communication system

An analytical investigation is made of the asymptotic propagation properties of pulses evolving from nonsoliton initial conditions in an optical-fiber communication system. Explicit analytical results are obtained for the characteristic parameters of the asymptotically emerging soliton as well as of the accompanying decaying nonsoliton part. The importance of the dispersively decaying part of the pulse for a soliton-based optical-fiber communication system is especially emphasized.