Pulses In Media Research Articles

Nonlinear Optical Pulses in Media with Asymmetric Gain.

A generic novel model governing optical pulse propagation in a nonlinear dispersive amplifying medium with asymmetric (linear spectral slope) gain is introduced. We examine the properties of asymmetric optical pulses formed in such gain-skewed media, both theoretically and numerically. We derive a dissipative optical modification of the classical shallow water equations that highlights an analogy between this phenomenon and hydrodynamic wave breaking. These findings provide insight into the nature of asymmetric optical pulses capable of accumulating large nonlinear phase without wave breaking, a crucial aspect in the design of nonlinear fiber amplifiers.

Linear pulse propagation with high-order dispersion

We present an approximate, but intuitively appealing theoretical study of the linear propagation of optical pulses in media with high-order dispersion. Our analysis, which is fully consistent with numerical simulations, is based on the pulses’ full-width at half maximum and shows that the effect of high-order dispersion differs significantly from that of the well-understood second order dispersion. For high dispersion orders m, the central part of the pulses, where the intensity is highest, evolve in the same way, independent of m, though at different rates, with a weak dependence on the initial pulse shape. We also find that all pulses, irrespective of initial pulse shape, eventually evolve to a sinc function. Our treatment allows us to find expressions for the characteristic dispersion lengths for high dispersion orders.

Investigation of congruent lithium niobate crystal dispersion properties in the terahertz frequency range

Dispersion curves of the refraction index of a congruent lithium niobate (cLN) crystal cut perpendicular to the x and z axes in the terahertz frequency range are considered. In the study, the method of terahertz time domain spectroscopy with time resolution is used passed through an initially isotropic detecting crystal which becomes birefringent when exposed to a terahertz field. The magnitude of the induced birefringence is proportional to the amplitude of the terahertz field. Using Fourier analysis of a terahertz pulse passing through a cLN crystal and a reference pulse that does not interact with the object, the frequency dependences of the refractive index and the absorption coefficient of the object under study are constructed. Dispersion curves are presented for the real part of the refractive index of a cLN crystal cut along the planes (100) and (001), in the frequency range 0.25–1.25 THz. Simulation of the propagation of a one-and-a-half-cycle pulse in media with dispersion is performed based on the data of scientific papers by other authors. As a result, the temporal forms of the output signals are found. Conclusion about the inaccuracy of the dispersion curves from the selected works is made. The parameters has been identified whose optimization made it possible to eliminate inaccuracies in the display of the dispersion dependence for the high-frequency region of the terahertz spectrum were identified. The results obtained are very important for the design of devices based on nonlinear optical effects. These data will be useful for the generation of difference frequencies, optical rectification and generation of terahertz radiation as well as for areas where accurate data on the terahertz dispersion properties of nonlinear crystals, including cLN, are required.

Adult Emergence of <em>Sitophilus oryzae</em> (L.) (Coleoptera: Curculionidae) in Stored Rice Varieties and Pulses with Broken Grains

The rice weevil, Sitophilus oryzae, is a serious pest of stored paddy and rice. Much information on its development during the storage of traditional and new improved rice varieties is not found in Sri Lanka. During milling, some percentage of rice is broken, and broken rice generally enhances the development of insects. However, the ability of progeny development of S. oryzae in the presence of broken rice particles is unknown. Hence, this study was conducted to assess the progeny development of S. oryzae in different rice and pulse media with a variable percentage of broken grains. Locally-available rice varieties, Red Kekulu, Red Samba, Red Heeneti, Kuruluthuda, Suwandel and the pulses, cowpea, greengram and blackgram having different broken percentages were tested for progeny adult emergence at 2, 4 and 6 weeks following initial infestation. The number of adults emerged varied with the grain type, broken percentage and the duration following initial infestation. Greengram (0-1.5) and blackgram (0-0.75) had very low adult emergence while Red Heeneti (0-191.75) and Red Kekulu (0.25-194.67) had the maximum adult emergence. The increase of the broken percentage initially increased the adult emergence and then decreased. The study concluded that S. oryzae adult emergence followed a trend of initial increasing and decreasing trend at the latter part in the samples with increasing percentages of broken rice. The adult emergence was higher at intermediate duration following infestation than the first and last durations. Future studies are needed to determine the reasons underlying the variation in the adult emergence across different grain types and broken percentages.

Self-Similar Optical Pulses in Media with Quadratic Nonlinearity and Absorption

Possibilities are studied for forming and preserving the two-frequency soliton-like state, allowing for the influence of two-photon absorption. The negative effect third-order dispersion has on the preservation of the self-similar mode is revealed during a numerical experiment.

Diffraction Limit in Theory of Light Bullets

An averaged variational procedure has been developed to study the propagation of light bullets in optical fibers using the propagation of light pulses in media with Kerr and quadratic nonlinearities as examples. Criteria for the correct choice of trial solutions are discussed. The condition under which the dispersion length is much greater than the length of diffraction spreading is called the diffraction limit. It is shown that, in this limit, the temporal and spatial dynamics of a bullet are independent of each other, while finding the dynamic parameters of a soliton is reduced to finding various solutions of the nonstationary linear Schrodinger equation for an imaginary quantum particle. The efficiency of the proposed approach is demonstrated by the example of finding solutions in the form of optical vortices in a waveguide for nonlinearities of both types.

Generation of few-cycle pulses in media with alternating sign of effective cubic nonlinearity

An original technique is developed for spectral broadening of femtosecond pulses with compensation for the nonlinear spatial phase during the propagation through nonlinear media with effective cubic nonlinearity of different signs. It was shown that in the region of 1.5 μm, the proposed scheme with BBO crystals at the first stage and NaCl at the second stage allows, using chirped mirrors, the formation of few-cycle pulses of about 7 fs duration with a small B-integral. The possibility of focusing of pulses compressed in the proposed scheme with a large Strehl ratio is demonstrated.

Acoustic Pulses in Media with Power Law Hysteretic Nonlinearity

Acoustic Pulses in Media with Power Law Hysteretic Nonlinearity

Transformation of the airy pulse at temporary jump of the dielectric permittivity of the medium

The spatio-temporal problem of interaction of the Airy electromagnetic pulse and a plane dielectric layer is solved in the case of a permittivity sharp change in a layer at zero moment of time. Expressions for the field inside the layer are obtained and the influence of the starting parameter on the position of the pulse inside the layer is shown. The evolution of the pulse in media with different refractive index is analyzed. A comparative analysis of the interaction of the Airy pulse with a plane layer between two dielectric media with a dielectric layer is carried out. The influence of pulse reflections from the layer boundaries on its shape and location is analyzed. From the analysis of the obtained results it follows that the choice of the initial space-time parameter affects the location of the pulse in the layer, and the transition of the signal to a medium with a larger (lower) permittivity results in the amplitude increase of oscillations and the main lobe shape change.

Collisions, mutual losses and annihilation of pulses in a modular nonlinear medium

One of the most important sections of nonlinear wave theory is related to the collisions of single pulses. These often exhibit corpuscular properties. For example, it is well known that solitons described by the Korteweg–de Vries equation and a few other conservative model equations exhibit properties of elastic particles, while shock waves described by dissipative models like Burgers’ equation stick together as absolutely inelastic particles when colliding. The interactions of single pulses in media with modular nonlinearity considered here reveal new physical features that are still poorly understood. There is an analogy between the single pulses collision and the interaction of clots of chemical reactants, such as fuel and oxidant, where the smaller component disappears and the larger one decreases after a reaction. At equal “masses” both clots can be annihilated. In this work various interactions of two and three pulses are considered. The conditions for which a complete annihilation of the pulses occurs are indicated.

Using self-phase modulation for temporal compression of intense femtosecond laser pulses

We report a theoretical analysis of the spectrum broadening of intense chirped femtosecond pulses in media with cubic nonlinearity. Subsequent temporal compression of such pulses using a quadratic spectral phase corrector is investigated. Pulse compression from 57 fs to 22 fs is demonstrated experimentally in a petawatt laser beam.

Nonanalytic pulse discontinuities as carriers of information

In this paper, we consider optical pulses encoded with two nonanalytic points, and we evaluate the detectable information of these pulses in media supporting slow- and fast-light propagation. It is shown that, in some configurations of slow- (subluminal) light propagation, the signal is not readily detectable, albeit the arrival of the encoded nonanalytic points at the receiver. It is thus argued that, from a practical point of view, information should not be entirely associated with the pulse discontinuities. On the other hand, it is confirmed that for propagation in vacuum or a fast-light medium, detectable information is bounded by the nonanalytic points, which create a space-time window within which detectable information cannot escape. As such, the distinction between the nonanalytic points of a signal, its energy transport, and detectable information is demonstrated.

Study of chiroptical fiber nonlinearities with new formulation of constitutive equations

A theoretical study of a light pulse propagating in a chiroptical fiber considering with Kerr effect is presented in this article. The novel effects of chirality are characterized through our proposed formalism, to highlight the nonlinear effect in a chiral medium, which is due to the magnetization vector under the influence of a strong electric field. These simulations are based on the split-step Fourier method for solving the nonlinear Schrödinger equation. The latter is one of the most used pseudo-spectral methods to study the propagation of pulses in media, nonlinear, and dispersive. The obtained results presented in this article illustrate nonlinear chirality parameter that becomes the key factor to estimate chiroptical fiber dispersion and nonlinearity.

Propagation of time-truncated Airy-type pulses in media with quadratic and cubic dispersion.

In this paper, we describe analytically the propagation of Airy-type pulses truncated by a finite-time aperture when second- and third-order dispersion effects are considered. The mathematical method presented here, which is based on the superposition of exponentially truncated Airy pulses, is very effective and allows us to avoid the use of time-consuming numerical simulations. We analyze the behavior of the time-truncated ideal Airy pulse and also the interesting case of a time-truncated Airy pulse with a "defect" in its initial profile, which reveals the self-healing property of this kind of pulse solution.

Abstract 326: Streptococcal Serum Opacity Factor Product, Cholesteryl Ester Rich Particles, Induce Cholesterol Ester Metabolism and Bile Acid Secretion after Uptake by Human Huh7 Hepatocytes

Plasma concentrations of HDL-cholesterol (C) negatively correlate with atherosclerotic cardiovascular disease. Nevertheless, current evidence suggests that this correlation is not axiomatic and that some forms of HDL are dysfunctional and atherogenic. Interventions that raise HDL-C have not been uniformly successful suggesting that mechanisms by which HDL-C is increased determine its anti atherogenic potency. Additionally, mice overexpressing the HDL receptor, SR-BI, have lower plasma HDL-C levels and less atherosclerosis. Thus, new strategies that reduce HDL-C while promoting reverse cholesterol transport (RCT) may have therapeutic value. Serum opacity factor (SOF) disrupts HDL and forms three products, including a cholesteryl ester-rich microemulsion (CERM) containing apo E and the CE of ~400,000 HDL particles. Hepatic CE uptake in Huh7 cells is faster when delivered by CERM than by HDL, and cleared both in vitro and in vivo, in part, via the LDL-receptor (LDLR). We investigated the therapeutic potential of SOF in promoting RCT by comparing the final RCT steps, hepatic uptake, CE metabolism to cholesterol and bile salts, and secretion, of [ 14 C]-CE-HDL, -CERM and [[Unable to Display Character: –]]LDL. Cells were pulse-labeled for 2 h with 20-50 ug/mL HDL protein (6-17 ug/mL [ 14 C]-CE), or the CE-equivalent as CERM or LDL, and chased for 0, 2 or 6 h. Cells, pulse media and chase media were analyzed for sterols by beta-counting, TLC and solvent partitioning. [ 14 C]CE uptake from LDL was greater than from CERM (2-4X) and HDL (5-10X). Halftimes for [ 14 C]CE hydrolysis were 3.0 ± 0.2, 4.4 ± 0.6 and 5.4 ± 0.7 h respectively for HDL, CERM and LDL-CE. Bile acids in cells after uptake from HDL or CERM were low, <0.2% of total sterol but higher in cells after uptake from LDL, 4.2 ± 2.2 % of total sterol ( p = 0.03 ) at the 2 h chase time. The fraction of sterols secreted as bile acids was comparable for all three donor particles. After the 2 h chase, ~40% of the secreted sterols were bile acids, and after 6 h, ~ 50% were bile acids. These ratios were the same for cells treated with 14 C-CE-HDL, CERM or LDL. Thus, the rates of hepatic metabolism of CERM-CE to free cholesterol, to bile acids and secretion are intermediate between those for HDL- and LDL-CE, supporting the therapeutic potential of SOF as a promoter of RCT.

Propagation of unipolar perturbations in hysteretic media with saturation of nonlinear losses

The propagation and evolution of unipolar perturbation pulses in hysteretic media with saturation of nonlinear losses have been theoretically studied. An exact analytical solution that describes the propagation and evolution of initially triangular pulses in these media has been obtained. Numerical and graphic analyses of the obtained solution are presented.

Pulse-by-pulse method to characterize partially coherent pulse propagation in instantaneous nonlinear media

We propose a numerical method for analyzing extensively the evolution of the coherence functions of nonstationary optical pulses in dispersive, instantaneous nonlinear Kerr media. Our approach deals with the individual propagation of samples from a properly selected ensemble that reproduces the coherence properties of the input pulsed light. In contrast to the usual strategy assuming Gaussian statistics, our numerical algorithm allows us to model the propagation of arbitrary partially coherent pulses in media with strong and instantaneous nonlinearities.

Propagation of unipolar strain pulses in media with hysteretic nonlinearity

A theoretical study of the propagation of unipolar strain pulses in a solid medium with an arbitrary power-law hysteretic nonlinearity is carried out. Exact analytical expressions are derived for describing the propagation and evolution of initially sine-shaped and triangular pulses in such media. The solutions found are analyzed both numerically and graphically.

Beyond the spatio-temporal model in femtosecond optics

We use the method of amplitude envelopes to obtain a class of linear nonparaxial amplitude equations, governing the propagation of short optical pulses in media with dispersion, dispersionless media and vacuum. The equations are solved using the method of Fourier transforms and fundamental and exact analytical solutions are obtained. Nonparaxiality leads to nonsymmetrical diffraction enlargement of light pulses and to their transformation in light disks on several diffraction lengths.

Diffraction of femtosecond pulses; nonparaxial regime

We present a systematic study of linear propagation of ultrashort laser pulses in media with dispersion, dispersionless media, and vacuum. The applied method of amplitude envelopes makes it possible to estimate the limits of the slowly varying amplitude approximation and to describe an amplitude integrodifferential equation governing propagation of optical pulses in the single-cycle regime in solids. The well-known slowly varying amplitude equation and the amplitude equation for the vacuum case are written in dimensionless form. Three parameters are obtained defining different linear regimes of optical pulse evolution. In contrast to previous studies we demonstrate that in the femtosecond region the nonparaxial terms are not small and can dominate over the transverse Laplacian. The normalized amplitude nonparaxial equations are solved using the method of Fourier transforms. Fundamental solutions with spectral kernels different from those according to Fresnel are found. Exact unidirectional analytical solution of the nonparaxial amplitude equations and the 3D wave equations with initial conditions compatible with Gaussian light bullets are obtained also. One unexpected new result is the relative stability of light bullets (pulses with spherical and spheroidal spatial form) when we compare their transverse enlargement with paraxial diffraction of light beams in air. It is important to emphasize here the case of light disks, i.e., pulses whose longitudinal size is small with respect to the transverse one, which in some partial cases are practically diffractionless over distances of a thousand kilometers. A new formula that calculates the diffraction length of optical pulses is suggested. Finally, propagation of single-cycle pulses in air and vacuum was investigated, and a coronal (semispherical) form of diffraction at short distances was observed.