Dynamics Of Pulse Propagation Research Articles

The effect of initial inversion of resonant atoms on the propagation dynamics of laser pulses in a continuous resonant photonic crystal

The nonlinear interaction of high-intensity coherent optical radiation and a continuous resonant photonic crystal is analytically and numerically studied in the framework of the semiclassical approximation using the two-wave Maxwell-Bloch equations at various initial excitations of resonant atoms. It is demonstrated that the initially unexcited resonant photonic crystal with an arbitrary concentration function of resonant atoms allows the propagation of the Bragg soliton of the self-induced transparency. The Bragg reflection is suppressed at zero initial inversion when the number of atoms in the excited state is equal to the number of atoms in the stationary state.

Controllable twin laser pulse propagation and dual-optical switching in a four-level quantum dot nanostructure

We investigate control of the propagation dynamics of weak twin laser pulses and propose a dual-optical switching scheme in four-level semiconductor quantum dots of diamond configuration. It is shown that the propagation dynamics of the two probe pulses depend not only on the intensity of corresponding control field in each cascade transition path but also on the relative intensities of the two control fields. This property provides the probability for realizing all-optical switching in the quantum dots. Possible all-optical switching operations for any one of the probe fields or both probe fields simultaneously with the same or adverse switching status can be realized by modulating the corresponding control fields. In addition, the relative phase of the laser fields also influences the switching operation and can be used to realize optical switching, which is also discussed in the paper.

Dynamics of ultrashort pulse propagation in the multilayer graphene-boron nitride system

The propagation of an ultrashort optical pulse in a multilayer structure formed by alternating graphene and boron nitride layers has been considered. Conduction electrons of this system have been described within the long-wavelength effective Hamiltonian in the case of low temperatures, and the electromagnetic field has been taken into account based on classical Maxwell’s equations. The dependence of the evolution on the velocity and maximum amplitude of the ultrashort pulse has been revealed.

Ultrafast Magnetoacoustics in Nickel Films

We report about the magnetization dynamics of a ferromagnetic nickel film at room temperature excited by acoustic pulses generated with femtosecond laser pulses. The ultrafast change of magnetization is detected from both the front and back sides of the nickel film. The propagating strain associated with the acoustic pulses modifies the magnetic anisotropy and induces a precession of the magnetization. We model the time-dependent magnetoacoustic response of the metallic film by combining a three temperature model for the temperatures of the charges, the spins, and the lattice, the wave equation for the strain, and the Landau-Lifshitz-Gilbert equation for the magnetization. It is shown that the precession dynamics can be controlled by matching the precession period with the round trip time of the acoustic echoes. The calculation of the time-dependent precession torque τ=|M×H(eff)| allows understanding the underlying physics.

Time-resolved single-shot imaging of femtosecond laser induced filaments using supercontinuum and optical polarigraphy

We have developed an ultrafast time-resolved imaging technique for the propagation dynamics of ultrashort laser pulses in transparent media. This method utilizes the optical polarigraphy technique and a chirped supercontinuum as the probe light. The supercontinuum senses the instantaneous birefringence induced by the propagation of an intense pulse, and a polarigraphy image with different color distributions could be obtained. Using this method, we performed a space-time characterization of the filament induced by a femtosecond laser pulse in CS2, indicating that this technique could be used for the single-shot imaging of pulse propagation dynamics.

Propagation dynamics of nonlinear chirped optical laser pulses in a two-level medium

We investigate the propagation dynamics of nonlinear chirped optical laser pulses in a two-level medium. For certain chirp strength and chirp width, an incident 2π nonlinear chirped pulse will split into optical precursors and a stable self-induced transparency soliton. This is caused by the particular Fourier spectrum that includes not only central resonant frequency components but also high-frequency and low-frequency sidebands. Moreover, the effects of chirp parameters on the evolution of nonlinear chirped pulses are also discussed.

Dark Solitons for a Generalized Korteweg-de Vries Equation with Time-Dependent Coefficients

We consider the evolution of long shallow waves in a convecting fluid when the critical Rayleigh number slightly exceeds its critical value within the framework of a perturbed Korteweg-de Vries (KdV) equation. In order to study the wave dynamics of nonlinear pulse propagation in an inhomogeneous KdV media, a generalized form of the considered model with time-dependent coefficients is presented. By means of the solitary wave ansatz method, exact dark soliton solutions are derived under certain parametric conditions. The results show that the soliton parameters (amplitude, inverse width, and velocity) are influenced by the time variation of the dependent model coefficients. The existence of such a soliton solution is the result of the exact balance among nonlinearity, third-order and fourth-order nonlinear dispersions, diffusion, dissipation, and reaction.

Quantum coherence effects in a Raman amplifier

We have studied optical pulse propagation in a Raman fiber amplifier doped with a three-level medium and driven by a control laser pulse. We analyze the spatial-temporal dynamics of pulse propagation for different atomic initial conditions. The propagation of an optical pulse through the amplifier can be sustained by a control laser that induces transparency via quantum coherence, which is useful for extending the distance between optical repeaters. Under certain conditions, amplification is achieved without population inversion. The results could be useful for laser control of optical pulses in amplifiers and waveguides.

A “Localized Pulse–Moving Front” Pair in a System of Coupled Complex Ginzburg–Landau Equations

A system of nonlinearly coupled complex Ginzburg–Landau equations, CGLEs, serves as a simple model for the dynamics of pulse propagation in dissipative, inhomogeneous media under the combined influence of dispersion, self and cross phase modulations, linear and nonlinear gain or loss. A solitary pulse (SP) is a localized wave form, and a kink or a front refers to a transition connecting two constant, but unequal, asymptotic states. Exact expressions for a “solitary pulse–kink” pair are obtained by a modified Hirota bilinear method. Parameters for these wave configurations are governed by a system of six algebraic equations, allowing the amplitudes, frequencies, and velocities to be determined. Exact solutions for special cases of the dispersive and nonlinear coefficients are obtained by computer algebra software.

Coherently induced double photonic band gaps in a driven N-type atomic system

In an N-type atomic system with double electromagnetically induced transparency, when the traveling-wave coupling field is replaced by a standing-wave, double fully developed photonic band gaps open up due to space-modulated refractive index within the two electromagnetically induced transparency widows. The dynamically induced band gaps can be tuned coherently, and have applications in manipulating the propagation dynamics of light pulses.

Pulse propagation in a decoupled two-core fiber

It is known that a decoupled two-core fiber can prevent monochromatic light at a specific wavelength (the decoupling wavelength) launched into one core from coupling to the other core. In this paper, we show that a pulse at the decoupling wavelength launched into one core of such a fiber inevitably splits into two pairs of pulses propagating in the two cores along the fiber. The minimum distance required for pulse splitting to be visible is inversely proportional to the coupling-coefficient dispersion in the fiber and linearly proportional to the pulse width. It would take only several centimeters of a recently demonstrated decoupled two-core photonic-bandgap fiber to observe the pulse-splitting effect with a 100-fs pulse. We also study the effects of self-phase modulation on the pulse propagation dynamics in a decoupled two-core fiber in both the normal and anomalous dispersion regimes.

Dynamics and control of few-cycle ultrashort pulse propagation in an asymmetric coupled-quantum-well nanostructure

The nonlinear propagation of few-cycle ultrashort pulse in an asymmetric coupled-quantum-well (CQW) nanostructure is simulated by solving numerically the full Maxwell–Bloch equations with an iterative predictor–corrector finite-difference time-domain method. The behaviors of electric field profiles for 2 π and 4 π ultrashort pulses in different propagating zones are predicted in details beyond the slowly varying envelope and rotating-wave approximations. This investigation may provide a guideline for optimizing and controlling ultrashort pulses in solid-state media, which are promising for practical applications in high-speed optical communications.

Propagation of twin light pulses under magneto-optical switching operations in a four-level inverted-Y atomic medium

Propagation dynamics of twin laser pulses through a cold four-level inverted-Y atomic medium is investigated theoretically via switching on and off an external magnetic field under the application of a strong driving field. By numerically solving the coupled Bloch–Maxwell equations for atom and field simultaneously on a spacetime grid, our spatio-temporal results clearly show that dynamic control of twin-pulse propagation and magneto-optic dual switching operation are possible in such an inverted-Y system. The proposed scheme may be used for the design of magneto-optic switching and magneto-optic storage devices.

Experimental study on all-normal-dispersion mode-locked fiber laser with optimal spectral filtering position

Employing nonlinear polarization rotation, an all-normal-dispersion mode-locked fiber ring laser was constructed, in which a fiber filter with 10 nm bandwidth was used in the cavity to provide the additional self-amplitude modulation. The important role of the filter position plays in the high-chirped pulse shaping in the laser has been experimentally demonstrated by choosing different locations of the filter in the cavity. A mode-locked pulse series, with the averaged power of 922 mW, output pulse duration of 62 ps, and pulse repetition frequency of 266 MHz, corresponding to the pulse energy of 35 nJ, was obtained in the optimized filter position under a pump power of 320 mW. By the numerical simulation, the propagation dynamics of pulses in the three cases of spectral filter (SF) position in the cavity are obtained and analyzed. The optimal location of the SF is found, which is in agreement with our experimental result.

Dynamics of femtosecond supercontinuum generation in multimode fibers

We solve a system of generalized nonlinear Schrödinger equations to study the nonlinear dynamics of ultrashort pulse propagation in multimode fibers. Due to pulse walk-off, permanent intermodal power transfer between modes is observed even in absence of phase matching. The strength of intermodal effects is found to depend strongly on modal symmetries, which results in preferential coupling between the LP(0n) modes. The scaling of nonlinear multimode effects in large-core fibers for the generation of ultra-high power spectral density supercontinua is finally discussed.

Slow light propagation and amplification via electromagnetically induced transparency and four-wave mixing in an optically dense atomic vapor

We experimentally and theoretically analyze the propagation of weak-signal field pulses under the conditions of electromagnetically induced transparency (EIT) in hot Rb vapor, and study the effects of resonant four-wave mixing (FWM). In particular, we demonstrate that in a double-Λ system, formed by the strong control field with the weak resonant signal and a far-detuned Stokes field, both continuous-wave spectra and pulse propagation dynamics for the signal field depend strongly on the amplitude of the seeded Stokes field, and the effect is enhanced in optically dense atomic medium. We also show that the theory describing the coupled propagation of the signal and Stokes fields is in good agreement with the experimental observations.

Self-compression and controllable guidance of multi-millijoule femtosecond laser pulses

Self-compression of multi-millijoule femtosecond laser pulses and dramatic increase of the peak intensity are found in pressurized helium and neon within a range of intensity in which the ionization modification of the material parameters by the pulse is negligible. The pulse propagation is studied by the (3 + 1)-dimensional nonlinear Schrödinger equation including basic lowest order optical processes – diffraction, second order of dispersion, and third order of nonlinearity. Smooth and well controllable pulse propagation dynamics is found. Construction of compressed pulses of controllable parameters at given space target point by a proper chose of the pulse energy and/or gas pressure is predicted.

Propagation of non-linear ion-sound pulses in dusty plasma waveguides

There are a lot of objects in space associated with dusty plasma inclusions. Such inclusions may bear a prolonged shape and behave as waveguides for ion-sound waves. In the case of space plasmas, the dust particles can possess both negative charge, due to electron attachment, and positive one, due to photoionization. In this paper the propagation of linear and non-linear ion-sound wave pulses in the dusty plasma waveguides, possessing positive charge, is studied. It has been demonstrated that non-linear dynamics of baseband pulse propagation in plasma waveguide possesses essentially non-solitonic behavior. Namely, propagation of a long ion-sound pulse leads to an excitation of a shock-like wave but not a stable localized nonlinear pulse. Also, when a Korteveg–de Vries (KdV) soliton is incident onto the dusty plasma waveguide, some part of the soliton energy is captured by the waveguide and transformed into a multi-pulse structure. Additionally, an interaction of dusty plasma inclusions with KdV soliton can lead to the occurrence of transverse instabilities of the soliton and its eventual destruction.

Extreme nonlinear optics in a Kerr medium: Exact soliton solutions for a few cycles

Exact soliton solutions containing only a few cycles are found within the framework of a nonlinear full wave equation in a Kerr medium. It is proven numerically that they are stable and play a fundamental role in the pulse propagation dynamics. These wave solitons cover the range from the fundamental Schrodinger solitons, which occur for long pulses involving many field oscillations, to extremely short pulses, which contain only one optical period.

Mode-locked Yb-doped fiber laser with external compression to 89 fs in normal dispersion fiber

A practical ytterbium-doped mode-locked fiber source producing 89 fs pulses without an external bulk compensator was developed by investigating the pulse propagation dynamics in a mode-locked fiber laser with small average dispersion. Negatively chirped pulses are taken from the cavity and compressed in a standard output fiber resulting in high-quality pulses.