Interaction Of Ultrashort Pulses Research Articles

Propagation and interaction of ultra-short pulses in quadratic crystals with controlled dispersion

Propagation of ultra-short optical pulses in an environment with quadratic nonlinearity and modulated dispersion is studied. It is shown that periodic modulation of the velocity-mismatch sign and of the third-order dispersion coefficient allows one to suppress pulse scattering and decompression, which noticeably increases their interaction efficiency.

Ultrafast probing of light-matter interaction in a midinfrared quantum cascade laser

In this work, we study the interaction of ultrashort midinfrared pulses with the active medium of an InGaAs∕InAlAs∕InP quantum cascade laser emitting at an 11.7μm wavelength. Applying an electro-optic sampling technique allowed us to measure the complete phase resolved transmission spectra at operating conditions below and above lasing threshold in a spectral range much broader than the gain band width. Far below threshold, we locate broadband resonant absorption, which spectrally overlaps with the electrically induced gain, forming areas of net absorption and net gain. Above threshold, gain clamping is seen, and it is found that echoes delayed by the round trip time experience spectral pulse shaping converging toward the emission spectrum.

Interaction of ultrashort light pulses with carbon nanotubes

The possibility of existence of electromagnetic solitons in carbon nanotubes is investigated on the basis of the coupled equations for the classical distribution function of electrons in such nanotubes and the Maxwell equations for electromagnetic fields. Solitons arise due to the matched change in the classical distribution function and the electric field formed by nonequilibrium electrons of a carbon nanotube. The data of numerical calculations, indicative of the existence of solitons, are reported.

Interaction of ultrashort x-ray pulses withB4C, SiC, and Si

The interaction of 32.5 and 6 nm ultrashort x-ray pulses with the solid materials B4C , SiC, and Si is simulated with a nonlocal thermodynamic equilibrium radiation transfer code. We study the ionization dynamics as a function of depth in the material and modifications of the opacity during irradiation, and estimate the crater depth. Furthermore, we compare the estimated crater depth with experimental data, for fluences up to 2.2 J/cm2. Our results show that, at 32.5 nm irradiation, the opacity changes by less than a factor of 2 for B4C and Si and by a factor of 3 for SiC, for fluences up to 200 J/cm2. At a laser wavelength of 6 nm, the model predicts a dramatic decrease in opacity due to the weak inverse bremsstrahlung, increasing the crater depth for high fluences.

Energy and angular distribution of deuterons from high-intensity laser–target interactions

The formation of a high-energy ion beam suitable for driving nuclear fusion reactions and producing MeV neutrons was investigated. The interaction of intense ultra short laser pulses with a double-layer thin foil for the production of MeV deuterons was studied theoretically and numerically simulated using a two-dimensional electromagnetic particle-in-cell model. The directionality and energy of the deuteron beam, specifically the conversion efficiency of laser energy into deuteron kinetic energy, and deuteron energy and angular distribution functions are studied as a function of peak laser intensity, laser pulse duration and target thickness. A range of parameters was determined for which a highly directional deuteron beam is generated.

Spectral control over the interaction of ultrashort pulses in fiber lasers

The interaction of light pulses in passively mode-locked fiber lasers operating has been studied. The numerical simulation has been used to demonstrate that a narrow-band selector inserted in a laser cavity allows the character of the interaction to be changed: depending on the detuning of the selector passband from the center of the gain band, ultrashort pulses can both attract and repel one another. Peculiarities of the pulse interaction have been studied at different parameters of the laser system.

Simulation of interactions of high-intensity ultrashort pulses with dielectric filters

Modern table-top laser systems are capable of generating ultrashort optical pulses with sufficiently high intensity to induce nonlinear optical effects in many of the materials that are used in the construction of optical components. We discuss the interaction of such pulses with three types of dielectric filters: (a) dielectric stacks composed of a sequence of two dielectric layers with quarterwave optical thickness, (b) idealized rugate filters, i.e., filters with a refractive index profile that is sinusoidally modulated on the length scale of an optical wavelength, and (c) a rugate filter composed of two materials. We present finite difference time-domain (FDTD) computer simulations of optical pulse propagation through dielectric filters for pulses with widths in the range 5 to 100 fs and with peak intensities up to 10 TW/cm2. At low intensities the reflective properties of the dielectric filters determined using FDTD simulations are directly comparable to the results calculated using the characteristic matrix method, while at high intensities optical nonlinearity in the dielectric layers is responsible for a decrease in the reflectance of the filter and causes stretching and distortion of the reflected pulses.

All-optical coherent control of spin dynamics in semiconductor quantum dots

A new model for rigorous theoretical description of circularly (elliptically) polarized ultrashort optical pulse interactions with singly charged quantum dots embedded in semiconductor optical waveguides and microcavities is proposed. The method is based on self-consistent solution in the time domain of the vector Maxwell equations coupled via microscopic polarization to the coherent time-evolution equations of a discrete N-level quantum system in terms of the real pseudospin (coherence) vector. The model is applied to a 4-level system describing the optical dipole transitions of the trion state in a singly charged quantum dot. Selective optical excitation of specific spin states by predefined helicity of the optical field and an onset of self-induced transparency and polarized soliton formation in the nonlinear regime are numerically demonstrated

Spin‐dependent dynamics of ultrafast polarised optical pulse propagation in coherent semiconductor quantum systems

AbstractA new model for rigorous theoretical description of circularly (elliptically) polarised ultrashort optical pulse interactions with the resonant nonlinearities in semiconductor optical waveguides is proposed. The method is based on self‐consistent solution in the time domain of the vector Maxwell equations coupled via microscopic polarisation to the coherent time‐evolution equations of a discrete N‐level quantum system in terms of the real pseudospin (coherence) vector. The model is initially applied to a generic two‐level quantum system and subsequently to a 4‐level system describing the heavy‐hole excitonic transitions in low‐dimensional semiconductor systems, such as quantum wells and quantum dots. Selective optical excitation of specific spin states by predefined helicity of the optical field in the linear regime and an onset of self‐induced transparency and polarised soliton formation in the nonlinear regime are numerically demonstrated in both discrete‐level systems. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Numerical methods for the bidimensional Maxwell–Bloch equations in nonlinear crystals

Two numerical schemes are developed for solutions of the bidimensional Maxwell–Bloch equations in nonlinear optical crystals. The Maxwell–Bloch model was recently extended [C. Besse, B. Bidégaray, A. Bourgeade, P. Degond, O. Saut, A Maxwell–Bloch model with discrete symmetries for wave propagation in nonlinear crystals: an application to KDP, M2AN Math. Model. Numer. Anal. 38 (2) (2004) 321–344] to treat anisotropic materials like nonlinear crystals. This semi-classical model seems to be adequate to describe the wave–matter interaction of ultrashort pulses in nonlinear crystals [A. Bourgeade, O. Saut, Comparison between the Maxwell–Bloch and two nonlinear maxwell models for ultrashort pulses propagation in nonlinear crystals, submitted (2004)] as it is closer to the physics than most macroscopic models. A bidimensional finite-difference-time-domain scheme, adapted from Yee [IEEE Trans. Antennas Propag. AP-14 (1966) 302–307], was already developed in [O. Saut, Bidimensional study of the Maxwell–Bloch model in a nonlinear crystal, submitted (2004)]. This scheme yields very expensive computations. In this paper, we present two numerical schemes much more efficient with their relative advantages and drawbacks.

Frequency-resolved optical gating in the 155 µm band via cascaded chi^(2) processes

We investigate ultrashort-pulse interactions based on cascaded second-harmonic generation and difference-frequency generation and propose their use for frequency-resolved optical gating (FROG) at telecom wavelengths in a waveguide configuration. We show how a chi(2)-chi(2) FROG device could allow the efficient characterization of ultrashort pulses, with time resolutions well beyond the limits normally imposed by walk-off effects on single-step chi(2) FROG devices.

Inelastic processes in the interaction of an atom with an ultrashort electromagnetic pulse

Electron transitions occurring during the interaction of a heavy relativistic atom with a spatially inhomogeneous ultrashort electromagnetic pulse are considered by solving the Dirac equation. The corresponding transition probabilities are expressed in terms of known inelastic atomic form factors, which are widely used in the theory of relativistic collisions between charged particles and atoms. By way of example, the inelastic processes accompanying the interaction of ultrashort pulses with hydrogen-like atoms are considered. The probabilities of ionization and production of a bound-free electron-positron pair on a bare nucleus, which are accompanied by the formation of a hydrogen-like atom in the final state and a positron in the continuum, are calculated. The developed technique makes it possible to take into account exactly not only the spatial inhomogeneity of an ultrashort electromagnetic pulse, but also the magnetic interaction.

Novel applications of short and ultra-short pulses

This paper offers recent successful examples for the application of nanosecond (ns) as well as picosecond (ps) and femtosecond (fs) laser pulses to media of gaseous, liquid or solid nature via non-linear interactions as a review, the laser ignition and dental ultra-short pulse interaction being parts of the authors’ own work. Plasma-initiated ignition of combustible gas mixtures represents a potential alternative way for long-lasting operation of gas engines with rather clean exhaust. Ultra-short pulses are useful for materials processing including dental hard tissue. Using miniaturized scanners of different types yields perfect cavity sizes without collateral damage at ablation rates coming close to mechanical drills in dentistry.

Interaction of a Hydrogen-Like Atom with an Ultrashort Pulse of Electromagnetic Waves

In the approximation of sudden perturbations, a solution of the Dirac equation describing the behavior of a hydrogen-like atom interacting with a spatially inhomogeneous ultrashort pulse of electromagnetic waves is derived. As an example, the single-electron inelastic processes accompanying the interaction of ultrashort pulses with hydrogen-like atoms are considered. The method developed here allows the spatial inhomogeneity of the ultrashort pulse of electromagnetic waves to be taken into account.

Numerical study of K-α emission from ultrashort-pulse laser-target interactions

K-α emission from ultrashort-pulse laser interactions with solid targets is studied here by means of numerical simulations. Fast electron generation by p-polarized laser beam obliquely incident on solid target is treated by 1D3V PIC code. Fast electron transport into the target and K-α emission is modeled by our time resolved 3D Monte Carlo code. We show here that self-induced electric fields have a serious impact on fast electron transport in dielectric materials. The influence of self-induced electric field on K-α emission energy from aluminum target with a thin surface dielectric layer is presented.

Emission of an atom during its interaction with an ultrashort pulse of electromagnetic field

The electronic transitions and emission of an atom during its interaction with a spatially inhomogeneous ultrashort pulse of electromagnetic field are considered. The probabilities of excitation and ionization, as well as the spectra and cross sections of reemission of such a pulse by the atom, are obtained. As an example, the one-and two-electron inelastic processes accompanying the interaction of ultrashort pulses with hydrogen-and helium-like atoms are considered.

Emission and electron transitions in an atom interacting with an ultrashort electromagnetic pulse

Electron transitions and emission of an atom interacting with a spatially inhomogeneous ultrashort electromagnetic pulse are considered. The excitation and ionization probabilities are obtained as well as the spectra and cross sections of the reemission of such a pulse by atoms. By way of an example, one-and two-electron inelastic processes accompanying the interaction of ultrashort pulses with hydrogen-and helium-like atoms are considered. The developed technique makes it possible to take into account exactly the spatial non-uniformity of the ultrashort pulse field and photon momenta in the course of reemission.

Doubly phase-matched cascaded parametric wave mixing of ultrashort laser pulses

Doubly phase-matched cascaded parametric wave mixing of femtosecond laser pulses in tapered fibers is experimentally demonstrated. Fibers with an appropriately tailored dispersion profile allow simultaneous phase matching for two types of nonlinear-optical processes-third-harmonic generation and parametric four-wave mixing. Doubly phase-matched cascaded parametric interactions of ultrashort light pulses give rise to a manifold of new spectral components, expanding substantially the capabilities of the available laser sources of ultrashort pulses.

Coupled Maxwell-pseudospin equations for investigation of self-induced transparency effects in a degenerate three-level quantum system in two dimensions: Finite-difference time-domain study

We extend to more than one spatial dimension the semiclassical full-wave vector Maxwell-Bloch equations for the purpose of achieving an adequate and rigorous description of ultrashort pulse propagation in optical waveguides containing resonant nonlinearities. Our considerations are based on the generalized pseudospin formalism introduced by Hioe and Eberly [Phys. Rev. Lett. 47, 838 (1981)] for treatment of the resonant coherent interactions of ultrashort light pulses with discrete-multilevel systems. A self-consistent set of coupled curl Maxwell-pseudospin equations in two spatial dimensions and time for the special case of a degenerate three-level system of quantum absorbers is originally derived. Maxwell's curl equations are considered to be coupled via macroscopic medium polarization to the three-level atom model for the resonant medium. Two distinct sets of pseudospin equations are obtained corresponding to the TE- and TM-polarized optical waves. For the case of TM polarization, the electromagnetic wave is polarized in a general direction in the plane of incidence inducing two dipole transitions in a degenerate three-level system by each E-field component along the propagation axis and in transverse direction. We introduce a dipole-coupling interaction Hamiltonian allowing Rabi flopping of the population difference along and perpendicular to the propagation axis with frequencies depending on the corresponding field components. The relationship between the induced polarization and the state vector components that describe the evolution of the discrete-level system is derived in order to couple the quantum system equations to the Maxwell's curl equations. The pseudospin equations are phenomenologically extended to include relaxation effects by introducing nonuniform decay times corresponding to the various dipole transitions occurring in a three-level system. The system has been discretized using finite differences on a Yee grid and solved numerically by an iterative predictor-corrector finite-difference time-domain method. Self-induced transparency soliton propagation through a degenerate three-level quantum system of absorbers in two spatial dimensions and time is demonstrated in planar parallel-mirror waveguide geometries.

NUMERICAL STUDY OF ULTRASHORT LASER PULSE INTERACTIONS WITH METAL FILMS

A dual-hyperbolic two-step radiation heating model is presented to investigate ultrashort laser pulse interactions with metal films. This model extends Qiu and Tien's theory by including the effect of heat conduction in the lattice. In addition, the depth distribution of laser intensity is modified by adding the ballistic range to the optical penetration depth. The effects of temperature dependence of the thermophysical properties also are examined. For comparison, the proposed model and the existing theories, the parabolic two-temperature model, Qiu and Tien's theory, and Fourier's law, are solved using a mesh-free particle method. Numerical analysis is performed with gold films; the results are compared with experimental data of Qiu, Jubhasz, Suarez, Bron, and Tien, and Wellershoff, Hohlfeld, Gudde, and Matthais. It is shown that this current model predicts more accurate thermal response than the existing theories considered in this study. It is also found that the inclusion of the ballistic effect to the depth distribution of laser intensity significantly improves the melting threshold fluence prediction.