Self-induced transparency in a dispersive medium

The evolution of the electromagnetic field in a two-level medium occurring in a matrix with finite response time has been studied. An integrable variant of the Maxwell-Bloch equations with allowance for nonlinear dispersion is derived and solved using the inverse scattering problem. It is shown that the nonlinear dispersion caused by the finite response time of the matrix yields a new possibility of controlling soliton parameters. A particular case of the constructed model can be used to describe field pulses in the parameter domain that occurs between the regions of applicability of the quasi-monochromatic approximation and the approximation of unidirectional propagation of pulses with durations on the order of the oscillation period.     

Self-induced transparency of circularly polarized femtosecond pulses

The phenomenon of self-induced transparency in a two-level medium is studied using a new integrable set of evolution equations for the optical pulses with a duration on the order of the energy-transition oscillation period. A mathematical apparatus is developed for the inverse scattering problem and used to obtain solitonic solutions to the model. The characteristics of linearly and circularly polarized pulses are compared with each other.     

Self-induced acoustic transparency of three-component longitudinal-transverse pulses

The features of the nonlinear dynamics of three-component elastic pulses in a low-temperature crystal containing paramagnetic impurities of electron and nuclear spins have been analyzed in the slowly varying envelope approximation. The presence of the electron spin subsystem makes it possible to equate the velocities of longitudinal sound and transverse acoustic waves; as a result, all components of the strain field efficiently interact with each other through the nuclear spin subsystem. The system of equations for envelopes of harmonics of the components of the strain field and the spin variables has been derived. The relations between the amplitudes and phases of the components have been obtained, the spectral composition has been analyzed, and the regimes of acoustic transparency of three-component longitudinal-transverse pulses have been discussed.     

Self-induced transparency of very short optical pulses

Solutions to a first order wave equation, appropriate to ultrashort optical pulse theory and to the optical undamped Bloch equations are presented. Detuning is shown to play essential role in the physical interpretation of these solutions. Related cases have been discussed by Courtens and by Lee. It is noted that the rotating wave approximation introduces strong restrictions on the range of validity of possible solutions. Pulses with Lorentzian shapes, while implied by the equations, appear to be without physical significance.     

周期量级超短激光脉冲在近临界密度等离子体中形成的光孤子

利用一维粒子模拟程序，观测到周期量级的超短激光脉冲在等离子体中可以以孤子形式传播.它在一定密度等离子体中以较高的群速度向前传播，并在到达等离子体与真空界面时发生反射和透射.当入射激光脉冲强度增大时，非线性调制效应使它产生较大的频率下移，致使光孤子传播速度变小.另外，对于同样光强下的几十个周期以上的光脉冲，它在等离子体中传播时形成的则是一连串低频的被捕获在等离子体中的光孤子. 关键词： 光孤子 超短激光脉冲 等离子体 粒子模拟     

Self-induced transparency in a resonance medium with the dipole-dipole interaction

Propagation of a pulse of self-induced transparency in a resonance medium is discussed for the case when it is necessary to take into account the direct electric dipole-dipole interaction between atoms. An equation for the envelope of a wave packet—the sine-Gordon equation—is obtained for the case of durations short compared to ω ₀ ^?1 (ω₀ is the transition frequency). The dependence of the velocity and the amplitude of the soliton on the magnitude of the dipole-dipole interaction of atoms is examined in the adiabatic approximation.     

Ionization of a multilevel atom by ultrashort laser pulses

Specific features of ionization of single atoms by laser fields of a near-atomic strength are investigated. Calculations are performed for silver atoms interacting with femtosecond laser pulses with wavelengths λ = 800 nm (Ti:Sapphire) and λ = 1.064 μm (Nd:YAG). The dependences of the probability of ionization and of the form of the photoelectron energy spectra on the field of laser pulses for various values of their duration are considered. It is shown that the behavior of the probability of ionization in the range of subatomic laser pulse fields is in good agreement with the Keldysh formula. However, when the field strength attains values close to the atomic field strength, the discrepancies in these dependences manifested in a decrease in the ionization rate (ionization stabilization effect) or in its increase (accelerated ionization) are observed. These discrepancies are associated with the dependence of the population dynamics of excited discrete energy levels of the atom on the laser pulse field amplitude.     

Self-induced transparency in waveguides

A theory of self-induced transparency (SIT) in waveguides, covered by thin films (thickness d ? λ = 2π/cω) of a resonant substance, has been developed. The shape of a waveguiding soliton (waveguiding “2π”-pulse) has been determined, and its velocity as a function of the film thickness and other characteristics of the resonant layer has been investigated.     

Single-peaked self-induced transparency pulses in a degenerate resonant medium

We obtained new analytic closed form solutions for distortionless propagation of ultra-short optical pulses through a resonant medium with overlapping Q(j) transitions for j=2. The steady-state pulse shape of this solution has only one peak. Both 2π and 0π solutions are obtained.     

Self-induced transparency for love waves

A theory of self-induced transparency is constructed for the Love wave in a system which consists of a film lying on a semispace in the presence of paramagnetic impurities. The solution is obtained in the form of the 2π-pulse of McCall and Hahn for the Love wave. It is shown that the characteristic parameters of the nonlinear Love wave depend on the transverse-mode profile.     

Filamentation of ultrashort light pulses in a liquid scattering medium

We have studied filamentation of 1-ps laser pulses in a scattering medium (aqueous suspension of 2-μm polystyrene microspheres) and compared filamentation dynamics to that in pure water. Our results indicate that light scattering does not alter filamentation dynamics in general, but rather results in farther position of the nonlinear focus, shorter filament length, and the development of speckle structure in the peripheral part of the beam. The experimental observations are qualitatively reproduced by the numerical model which accounts for diffraction, self-focusing, multiphoton absorption, and light scattering introduced through a stochastic diffusion and diffraction term.     

微结构光纤中超短激光脉冲传输的数值模拟

在传统求解广义非线性薛定谔方程(GNSE)分步傅里叶方法的基础上，提出了利用自适应分步 傅里叶方法(ASSFM)求解GNSE.数值模拟发现：在发生显著孤子峰值频移且微结构光纤的色散 和非线性参数随频率显著变化的情况下，采用ASSFM对超短脉冲在光纤中传输进行模拟是很 必要的，微结构光纤色散特性对超短脉冲在微结构光纤中的演化以及超连续光谱展宽有很大 影响.ASSFM可以合理地考虑到微结构光纤特性参数随脉冲演化过程中峰值功率所对应波长（ 或频率）的变化，从而更精确地模拟超短脉冲在微结构光纤中的传输. 关键词： 微结构光纤 超短脉冲 色散 自适应分步傅里叶方法     

Propagation of the ultrashort laser pulses through the quantum nonlinear medium with resonant properties

The propagation of ultrashort few-cycle laser pulses through a quantum nonlinear medium with resonant properties is studied using the method of slowly varying amplitudes with allowance for dispersion effects. A self-consistent system of nonlinear wave equation for the evolution of laser field and the nonstationary Schrödinger equation that determines the material polarization response is numerically solved. Specific features of the propagation of laser pulse caused by a relatively large spectral width and the nonadiabatic character of the laser pulse are established. The rise of the slowly dumping polarization at the eigenfrequency of the medium and the consequent stretching of the laser pulse are observed. The role of the resonant absorption of the laser energy in the medium is analyzed. The nonlinear spectral broadening is demonstrated for the laser pulse propagating through the medium.     

Self-induced transparency in limited media

A theory is constructed of self-induced transparency for a surface wave, propagating on the boundary surface of two media, one of which is a resonance one, and also for a localized TE-mode in dielectric waveguide, containing non-intersecting two-level atoms. An evident expression is found for a pulsing solition, formed in these conditions, in terms of initial data.     

Self-induced transparency of hydrogen-containing ferroelectrics for extremely short pulses in the vicinity of the curie temperature

Nonlinear propagation of extremely short (carrierless) electromagnetic pulses in a KDP-type ferroelectric is investigated at temperatures close to the phase transition point. It is demonstrated that, although weak monochromatic signals undegro a sharp attenuation at these temperatures, an extremely short high-power pulse can propagate in the self-induced transparency regime and the associated soliton is stable to transverse perturbations.     

Influence of atomic densities on propagation property for ultrashort pulses in a two-level medium

The influence of atomic densities on the propagation property for ultrashort pulses in a two-level atom (TLA) medium is investigated. With higher atomic densities, the self-induced transparency (SIT) cannot be recovered even for 2π ultrashort pulses. New features such as pulse splitting, red-shift and blue-shift of the corresponding spectra arise, and the component of central frequency gradually disappears.     

Chalcogenide glasses as a medium for controlling ultrashort IR pulses: Part I

Chalcogenide glasses are ideal materials for developing fiber lasers and amplifiers, remote sensors, high-speed switches, and other devices that operate in the IR range of 1–10 μm. The nonlinear refractive index of chalcogenide glasses may exceed that of quartz glass by a factor of 100–1200 or even more. The data on the dispersion properties of some chalcogenide glass compositions in the IR range are presented. The possibility of forming waveguide structures with specified dispersion properties (in particular with a fixed wavelength at which the group velocity dispersion is zero) from these glasses is numerically investigated. It is shown by the example of completely glassy periodic waveguide structures with planar geometry that the use of photonic band gap modes makes it possible the change the position of zero dispersion in a wide wavelength range. In the calculations the contrast of waveguide structures was varied using parameters of glasses of different composition.     

Coherent forward four-wave mixing of ultrashort radiation pulses in a resonant medium

Forward four-wave mixing (FFWM) of ultrashort light pulses is considered theoretically under their coherent propagation in a resonant-absorbing medium. Nonlinear equations describing FFWM are obtained and studied and it is shown that the energy exchange between pulses of exact resonance may lead to the enhancement of weak radiation. The influence of input radiation parameters and interaction geometry on the FFWM characteristics has been studied.