Localized optical subcycle pulses in dispersive media

The conditions for creation of broadband localized optical fields (Bessel X pulses and focus wave modes) in dispersive media are analyzed. It is shown that transmission of focus wave modes with subcycle pulse durations through fused silica is possible.     

Ultimately short optical pulses in carbon nanotubes in dispersive nonmagnetic dielectric media

We consider Maxwell’s equations for an electromagnetic field propagating in carbon nanotubes placed in dispersive nonmagnetic dielectric media. An effective equation having the form of an analog of the classical sine-Gordon equation was obtained and analyzed numerically. The dependence of the pulse on the type of carbon nanotubes, initial pulse amplitude, and dispersion constants of the medium was revealed.     

Measurement of net group and reshaping delays for optical pulses in dispersive media

We experimentally demonstrate the direct measurement of net group and reshaping delays for arbitrary optical pulses in dispersive media, verifying the earlier prediction of Peatross et al. [Phys. Rev. Lett. 84, 2370 (2000)]. Incoherent pulse propagation in an absorptionless system is well described by net group delay; even the medium causes a great deal of deformation in the transmitted pulse. However, in the case of phase modulated chirping pulses in a resonant absorber, the so-called superluminal or subluminal propagation velocity is strongly influenced by the reshaping delay.     

Localized subluminal envelope pulses in dispersive media

The existence and properties of propagative nondispersive and nondiffracting localized envelope waves in dispersive transparent media, with either normal or anomalous group-velocity dispersion, showing subluminal group velocities and strong spatial localization are pointed out. Nonparaxial effects may lead to group-velocity reduction of several orders of magnitude. Numerical simulations are given for wave propagation in sapphire.     

Propagation of extremely short optical pulses in impurity carbon nanotubes in dispersive and nonlinear media

Maxwell equations describing an extremely short pulse propagating in impurity carbon nanotubes placed in a dispersive nonmagnetic medium are analyzed with allowance for the nonlinearity of the medium. The dependences of the magnetic field intensity on the initial pulse amplitude and the parameters of the medium are revealed.     

Dynamics of optical pulses in a dispersive chiral medium

The dynamics of frequency-modulated pulses in an isotropic nonreciprocal chiral medium is studied. It is shown that the discrepancy between the group velocities and carrier frequencies of the circular components of the pulse causes it to split up both along the fiber and in the spectral domain. The strong dependence of the material parameters on the pulse frequency may lead to the asymmetric dynamics of the electric and magnetic fields of the pulse in different frequency intervals. For both components of the wave field, envelopes moving with a supraluminal speed may arise.     

Near-field and far-field propagation of beams and pulses in dispersive media

We formulate an efficient exact method of propagating optical wave packets (and cw beams) in isotropic and nonisotropic dispersive media. The method does not make the slowly varying envelope approximation in time or space and treats dispersion and diffraction exactly to all orders, even in the near field. It can also be used to determine the partial differential wave equation for pulses (and beams) to any order as a power series in the partial derivatives with respect to time and space. The method can treat extremely focused pulses and beams, e.g., from near-field scanning optical microscopy sources whose transverse spatial extent in smaller than a wavelength.     

Spatio-temporal pulse propagation in nonlinear dispersive optical media

We discuss state-of-art approaches to modeling of propagation of ultrashort optical pulses in one and three spatial dimensions. We operate with the analytic signal formulation for the electric field rather than using the slowly varying envelope approximation, because the latter becomes questionable for few-cycle pulses. Suitable propagation models are naturally derived in terms of unidirectional approximation.     

Amplification of extremely short pulses in optical media

The dynamics of pulses with durations comparable to the inverse transition frequency that propagate in an optical medium is studied in terms of two integrable systems of Maxwell-Bloch equations. The first model describes the field interaction with a nondegenerate medium with a permanent dipole moment and permanent external pumping. A general formula is derived for the N-soliton solution. Particular solutions are used as examples to investigate the effect of permanent dipole moment and pumping on the soliton dynamics. The second model describes the interaction between two-component electric-field pulses and a two-level degenerate medium with permanent upper-level pumping. For different initial magnetic-sublevel populations, soliton solutions are used as examples to show that pumping causes a change in polarization dynamics. A two-soliton solution is used to analyze the interaction of solitons in a two-level medium with external pumping.     

Time-dependent velocities in porous media dispersive flow.

Pulsed Gradient Spin Echo (PGSE) NMR methods may be used to measure the asymptotic dispersion coefficient as well as the velocity autocorrelation function (VACF) in porous media flow. The VACF can be measured in the frequency domain using repetitive gradient pulse trains, and in the time domain using double PGSE encoding. The one dimensional double PGSE method, and the two dimensional velocity exchange experiment (VEXSY) are briefly outlined and their application to flow in monodisperse 0.5 mm diameter beads packs described, both axial and transverse VACFs being examined. The measured correlation times are shown to agree well with calculated values. The asymptotic dispersion coefficients agree with literature values in the case of transverse flow while in axial flow it is shown that asymptotic conditions are not achieved, even for observation times longer than the correlation time for flow around a bead.     

Effect of the intrinsic nonlinearity on the propagation of ultrashort optical pulses in carbon nanotubes in dispersive nonmagnetic dielectric media

The Maxwell equations for the electromagnetic field that propagates in carbon nanotubes (CNTs) placed in dispersive nonmagnetic dielectric media are analyzed with allowance for the intrinsic nonlinearity of the medium. The dependences of the pulse on the initial pulse amplitude, dispersion constants, and nonlinearity are revealed.     

Optical filaments and optical bullets in dispersive nonlinear media

We have investigated the evolution of picosecond and femtosecond optical pulses governed by the amplitude vector equation in the optical and UV domains. We have written this equation in different coordinate frames, namely, in the laboratory frame, the Galilean frame, and the moving-in-time frame and have normalized it for the cases of different and equal transverse and longitudinal sizes of optical pulses or modulated optical waves. For optical pulses with a small transverse size and a large longitudinal size (optical filaments), we obtain the well-known paraxial approximation in all the coordinate frames, while for optical pulses with relatively equal transverse and longitudinal sizes (so-called light bullets), we obtain new non-paraxial nonlinear amplitude equations. In the case of optical fields with low intensity, we have reduced the nonlinear amplitude vector equations governing the light-bullet evolution to the linear amplitude equations. We have solved the linear equations using the method of Fourier transform. An unexpected new result is the relative stability of light bullets and the significant decrease in the diffraction enlargement of light bullets with respect to the case of long pulses in the linear propagation regime.     

负啁啾高强度飞秒脉冲在正常色散材料中传输特性研究

利用块状正常色散材料作非线性介质，实验研究了负啁啾强激光飞秒脉冲在正常色散材料的传输过程中，脉冲波形及频谱随入射脉冲能量的变化特性.实验发现，负啁啾脉冲经过材料后激光光谱在被整形和压缩的同时，脉冲宽度也被压缩.实验获得的压缩脉冲宽度短于相等光谱宽度下的双曲正割转换极限脉冲宽度.数值模拟结果显示，在实验条件下模拟结果具有同样的变化特性. 关键词： 飞秒脉冲 自压缩 负啁啾 自聚焦     

Transverse instability of one-dimensional transparent optical pulses in resonant media

It is shown analytically that a transparent optical pulse in a resonant medium, i.e the SIT soliton, is unstable with respect to long transverse perturbations. In this limit, the growth rate as a function of the amplitude and phase of the pulse is derived.     

Self-induced thermal effects of optical pulses in model aerosol media

The self-broadening and intensity self-limiting of millisecond optical pulses in the nonlinear scattering of intense light in model aerosol media are investigated experimentally. The experimental results are compared with existing theoretical calculations.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 33–39, March, 1976.     

Three-dimensional evolution of ultrashort pulses in dispersive media beyond the slowly varying envelope approximation

A new analytical solution for the three-dimensional evolution of femtosecond pulses in a medium with group velocity dispersion is presented. It is found that for Gaussian pulses as short as a few optical cycles, the coupling between spatial and temporal parameters becomes important, which will cause breakdown of the slowly varying envelope approximation (SVEA) equation.     

Singularities of the Hele-Shaw flow and shock waves in dispersive media

We show that singularities developed in the Hele-Shaw problem have a structure identical to shock waves in dissipativeless dispersive media. We propose an experimental setup where the cell is permeable to a nonviscous fluid and study continuation of the flow through singularities. We show that a singular flow in this nontraditional cell is described by the Whitham equations identical to Gurevich-Pitaevski solution for a regularization of shock waves in Korteveg-de Vriez equation. This solution describes regularization of singularities through creation of disconnected bubbles.