Interaction Of Ultrashort Pulses Research Articles

Modeling of the interaction of an x-ray free-electron laser with large finite samples.

We describe a model for the study of the interaction of short x-ray free-electron laser (XFEL) pulses with large finite samples. Hydrodynamics is solved in one-dimensional planar geometry with consideration of the electron-ion energy exchange and of the possible elastoplastic behavior. From a time-dependent calculation of the complex refractive index and of the underlying atomic physics, XFEL energy deposition is modeled through a calculation of the radiation field in the material. In the case of hard x-ray irradiation, energetic electrons induced by the XFEL absorption can propagate and deposit their energy outside the interaction region. Simulations of the interaction of hard x-ray ultrashort pulses with solid materials Ru and Si at different grazing incidence angles are presented and discussed. The results obtained demonstrate the potential of this approach to predict damage dynamics for materials of interest for x-ray optics.

THz radiation generation via the interaction of two‐colour ultra‐short laser pulses with SO2 and NH3 gases

In this work, using a two‐dimensional particle‐in‐cell Monte Carlo collision computation method, terahertz (THz) radiation generation via the interaction of two‐colour, ultra‐short, high‐power laser pulses with the polyatomic molecular gases sulphur dioxide (SO2) and ammonia (NH3) is examined. The influence of SO2 and NH3 pressures and two‐colour laser pulse parameters, i.e., pulse shape, pulse duration, and beam waist, on the THz radiation generation is studied. It is shown that the THz signal generation from SO2 and NH3 increases with the background gas pressure. It is seen that the THz emission intensity for both gases at higher laser pulse durations is higher. Moreover, for these polyatomic gases, the plasma current density increases with increase in the laser pulse beam waist. A more powerful THz radiation intensity with a larger time to peak of the plasma current density is observed for SO2 compared to NH3. In addition, many THz signals with small intensities are observed for both polyatomic gases. It is seen that for both SO2 and NH3 the generated THz spectral intensity is higher at higher gas pressures.

Cross-polarized, multi-octave supercontinuum generation.

The generation of superoctave spectra from the interaction of intense ultrashort optical pulses and cubic nonlinearity is the result of interplay between the dispersion and nonlinearity of a material and various propagation effects. The cubic nonlinearity can be enhanced when it is combined with a quadratic-cascaded nonlinearity, relaxing the requirement on the laser's peak intensity for supercontinuum (SC) generation. In this Letter, we demonstrate and compare the generation of an SC driven from cubic and cascaded quadratic nonlinearities at an anomalous and zero dispersion wavelength (ZDW). We show the filament-free SC generation of femtosecond mid-infrared pulses by harvesting cascaded quadratic nonlinearity and, at ZDW, requires a lower threshold peak intensity and results in a higher power spectral density for the newly generated spectral components. The presented method is a suitable approach for generating multi-octave spectra from low peak-power, high average-power oscillators or a suitable seed for optical parametric amplifiers and multi-octave field synthesizers.

Ultrashort dark solitons interactions and nonlinear tunneling in the modified nonlinear Schrödinger equation with variable coefficient

Abstract We present the study of the dark soliton dynamics in an inhomogeneous fiber by means of a variable coefficient modified nonlinear Schrodinger equation (Vc-MNLSE) with distributed dispersion, self-phase modulation, self-steepening and linear gain/loss. The ultrashort dark soliton pulse evolution and interaction is studied by using the Hirota bilinear (HB) method. In particular, we give much insight into the effect of self-steepening (SS) on the dark soliton dynamics. The study reveals a shock wave formation, as a major effect of SS. Numerically, we study the dark soliton propagation in the continuous wave background, and the stability of the soliton solution is tested in the presence of photon noise. The elastic collision behaviors of the dark solitons are discussed by the asymptotic analysis. On the other hand, considering the nonlinear tunneling of dark soliton through barrier/well, we find that the tunneling of the dark soliton depends on the height of the barrier and the amplitude of the soliton. The intensity of the tunneling soliton either forms a peak or valley and retains its shape after the tunneling. For the case of exponential background, the soliton tends to compress after tunneling through the barrier/well.

Multiphase titanium oxide nanomaterial for augmented vis–NIR photon absorption

Nanomaterials based on titanium di-oxide (titania) are intensively being studied for their incorporation in the next generation photovoltaic devices due to titania׳s excellent photocatalytic properties. Inefficient utilisation of deeper visible and near infra-red region (NIR) photons has however limited the exploitation of such materials. In this paper, we report a unique titanium oxide nanomaterial that is sensitive to photons of wavelength even longer than 600nm and is composed of not one but multiple phases of titanium oxide. It has exhibited enhanced absorption that is three times greater in visible region and six times greater in NIR than base titanium. Synthesised by a phenomenon created via the interaction of ultrashort pulses with a titanium substrate, this photoabsorptive nanomaterial is dopant free and is structurally formed as a dense three dimensional network. Further effective tuning of the optical properties of the synthesised multiphase titanium oxide nanomaterial can make it a potential absorber material in photovoltaic devices.

Modeling femtosecond pulses in optical power splitter using time domain techniques

In this paper, time domain beam propagation method (TD-BPM) has been developed and implemented for analyzing short and ultra short pulse interaction inside optical power splitter. The results obtained by the technique has been compared to that of the finite difference time domain (FDTD) technique. The TD-BPM is as effective and stable on the properly designed device as on waveguide and directional coupler. Proper design of the device ensures minimum radiation loss enhancing the output power. Moreover, the TD-BPM provides complete visualization of the pulse in course of its propagation as the technique updates the spatiotemporal pulsed window with propagation step, unlike the FDTD where finely gridded device is updated with time. Being an implicit technique, it is free from Courant–Friedrich–Levy constraint and infinitesimal gridding.

Ultrashort Pulse Interaction with Intersubband Transitions of Semiconductor Quantum Wells

We study coherent ultrashort pulse propagation in a two-subband system in a symmetric semiconductor quantum well structure, performing calculations beyond the rotating wave approximation and the slowly varying envelope approximation and taking into account the effects of electron-electron interactions. The interaction of the quantum well structure with the electromagnetic fields is studied with modified, nonlinear, Bloch equations. These equations are combined with the full-wave Maxwell equations for the study of pulse propagation. We present results for the pulse propagation and the population inversion dynamics in the quantum well structure for different electron sheet densities.

Interaction of Ultrashort Pulses in Metallic Nanotubes

The wave equation for two ultrashort optical pulses propagating in metallic carbon nanotubes is analyzed. The behavior of electromagnetic pulses during a collision is examined as a function of their initial amplitudes and velocities. In the interaction of pulses of different amplitudes, absorption of the pulse with the smaller amplitude is observed.

Analysis of ultrashort laser pulse interactions with metal films using a two-temperature model

Journal of Applied Mathematics and Computational Mechanics, Prace Naukowe Instytutu Matematyki i Informatyki, Politechnika Częstochowska, Scientific Research of the Institute of Mathematics and Computer Science, Czestochowa University of Technology

Quantum coherent optical phase modulation in an ultrafast transmission electron microscope.

Coherent manipulation of quantum systems with light is expected to be a cornerstone of future information and communication technology, including quantum computation and cryptography. The transfer of an optical phase onto a quantum wavefunction is a defining aspect of coherent interactions and forms the basis of quantum state preparation, synchronization and metrology. Light-phase-modulated electron states near atoms and molecules are essential for the techniques of attosecond science, including the generation of extreme-ultraviolet pulses and orbital tomography. In contrast, the quantum-coherent phase-modulation of energetic free-electron beams has not been demonstrated, although it promises direct access to ultrafast imaging and spectroscopy with tailored electron pulses on the attosecond scale. Here we demonstrate the coherent quantum state manipulation of free-electron populations in an electron microscope beam. We employ the interaction of ultrashort electron pulses with optical near-fields to induce Rabi oscillations in the populations of electron momentum states, observed as a function of the optical driving field. Excellent agreement with the scaling of an equal-Rabi multilevel quantum ladder is obtained, representing the observation of a light-driven 'quantum walk' coherently reshaping electron density in momentum space. We note that, after the interaction, the optically generated superposition of momentum states evolves into a train of attosecond electron pulses. Our results reveal the potential of quantum control for the precision structuring of electron densities, with possible applications ranging from ultrafast electron spectroscopy and microscopy to accelerator science and free-electron lasers.

Computer Modeling of Ultra-Short Optical Pulses Interaction in Silicene

Computer Modeling of Ultra-Short Optical Pulses Interaction in Silicene

Theoretical analysis of hard x-ray generation by nonperturbative interaction of ultrashort light pulses with a metal.

The interaction of intense femtosecond pulses with metals allows for generating ultrashort hard x-rays. In contrast to plasma theories, tunneling from the target into vacuum is introduced as electron generation step, followed by vacuum acceleration in the laser field and re-entrance into the target to generate characteristic x-rays and Bremsstrahlung. For negligible space charge in vacuum, the Kα flux is proportional to the incident intensity and the wavelength squared, suggesting a strong enhancement of the x-ray flux by mid-infrared driving pulses. This prediction is in quantitative agreement with experiments on femtosecond Cu Kα generation.

Interaction of ultrashort pulses with molecules and solids: Physics and applications

The interaction of ultrashort laser pulses with molecules and solids is an extremely complex area of science research encompassing the fields of physics, chemistry, and materials science. The physics of interaction has been fairly understood over the last couple of decades and, consequently, several applications have been envisaged from these interactions in the fields of photonics, lithography, biomedicine, sensing, telecommunications etc. In the present article we describe three different components of interaction of ultrashort pulses with matter: (1) with liquid molecules/thin films wherein we present the results from our studies of optical nonlinearities predominantly using picosecond and femtosecond pulses, (2) with molecules/solids wherein plasma generated from the surface was studied for applications in understanding the molecular dynamics and towards identifying high-energy molecules and (3) within the bulk and on the surface of solids (e.g. glasses, bulk polymers and metals) resulting in micro- and nanostructures. Different applications resulting from such interactions in photonics and microfluidics are presented and discussed.

Analysis of femtosecond pulsed beam propagation in dispersive directional coupler

An analysis of ultrashort-pulse interaction inside directional coupler structures having dispersive material is conveyed using the well-known finite difference time domain (FDTD) technique and time domain beam propagation method (TD-BPM). The implicit TD-BPM uses a higher-order non-paraxial equation suitable for femtosecond pulse. The result obtained by the one-way technique is verified with that of the widely used FDTD. A rigorous study is conveyed in order to distinguish material dispersion from intermodal dispersion. The analysis reveals that material dispersion causes energy loss in the device, in addition to extra pulse broadening and splitting that occur to a low extent in the case of intermodal dispersion.

Reemission spectra and interference effects upon interaction of ultrashort electromagnetic pulses with nanosystems

The processes of reemission of ultrashort electromagnetic pulses by arbitrary nanosystems consisted of isolated complex atoms have been considered. The angular distributions of reemission spectra have been obtained for a series of regular nanosystems. It has been shown that the interference of the photon-emission amplitudes leads to the appearance of characteristic “diffraction” maxima. One-, two-, and three-dimensional nanostructures, as well as planar and cylindrical constructions as models of planar nanosystems and nanotubes, were used as examples that allow a simple analytical consideration.

Bright hump solitons for the higher-order nonlinear Schrödinger equation in optical fibers

Under investigation is the higher-order nonlinear Schrodinger equation with the third-order dispersion (TOD), self-steepening (SS) and self-frequency shift, which can be used to describe the propagation and interaction of ultrashort pulses in the subpicosecond or femtosecond regime. Through the introduction of an auxiliary function, bilinear form is derived. Bright one- and two-soliton solutions are obtained with the Hirota method and symbolic computation. From the one-soliton solutions, we present the parametric regions for the existence of single- and double-hump solitons, and find that they are affected by the coefficients of the group velocity dispersion (GVD) and TOD. Besides, propagation of the one single- or double-hump soliton is observed. We analytically obtain the amplitudes for the single- and double-hump solitons, and calculate the interval between the two peaks for the double-hump soliton. Moreover, soliton amplitudes are related to the coefficients of the GVD, TOD and SS, while the interval between the two peaks for the double-hump soliton is dependent on the coefficients of the GVD and TOD. Interactions are seen between the (i) two single-hump solitons, (ii) two double-hump solitons, and (iii) single- and double-hump solitons. Those interactions are proved to be elastic via the asymptotic analysis.

In search for the pairing glue in cuprates by non-equilibrium optical spectroscopy

In strongly correlated materials the electronic and optical properties are significantly affected by the coupling of fermionic quasiparticles to different degrees of freedom, such as lattice vibrations and bosonic excitations of electronic origin. Broadband ultrafast spectroscopy [1, 2] is emerging as the premier technique to unravel the subtle interplay between quasiparticles and electronic or phononic collective excitations, by their different characteristic timescales and spectral responses. By investigating the femtosecond dynamics of the optical properties of Bi2Sr2Ca0.92Y0.08Cu2O8+δ (Y-Bi2212) crystals over the 0.5–2 eV energy range, we disentangle the electronic and phononic contributions to the generalized electron-boson Eliashberg function [3, 4], showing that the spectral distribution of the electronic excitations, such as spin fluctuations and current loops, and the strength of their interaction with quasiparticles can account for the high critical temperature of the superconducting phase transition [5]. Finally, we discuss how the use of this technique can be extended to the underdoped region of the phase diagram of cuprates, in which a pseudogap in the quasiparticle density of states opens.The microscopic modeling of the interaction of ultrashort light pulses with unconventional superconductors will be one of the key challenges of the next-years materials science, eventually leading to the full understanding of the role of the electronic correlations in controlling the dynamics on the femtosecond timescale.

Bound states of dissipative solitons in fiber lasers with a lumped saturable absorber

The interaction of ultrashort pulses and their bound states in fiber lasers with a saturable absorber are analyzed by numerical simulation. It is shown that the distance between two interacting pulses in the lasing mode established after a transient process can take a set of quantized values in which neighboring pulse separations correspond to steady bound states of opposite parity. Characteristic changes in the established states with a change in the parameters of the laser system are demonstrated. The developed model of passive laser mode locking and the results presented in the paper can be used to describe and interpret the lasing modes of fiber lasers with nonlinear losses due to different nanomaterials (media with quanta wells, nanotubes, graphene, etc.).

Non-perturbative time-dependent numerical simulation for electromagnetically induced transparency and slow light in three-level Λ-type atoms

A time-dependent, semi-classical simulation model of light coupling with an array of three-level Λ-type atoms is developed to study dynamical phenomena of electromagnetically induced transparency (EIT). Light is described by electromagnetic wave equation and the quantum dynamics of atoms is described by time-dependent non-perturbative Schrödinger equation. Dynamical pictures and the mechanism of EIT are demonstrated and this model is used to explore the light–matter interaction of ultra-short pulse.

Signatures of collective electron dynamics in the angular distributions of electrons ejected during ultrashort laser pulse interactions with C+

We use the time-dependent R-matrix approach to investigate an ultrashort pump–probe scheme to observe collective electron dynamics in C+ driven by the repulsion of two equivalent p electrons. By studying the two-dimensional momentum distributions of the ejected electron as a function of the time-delay between an ultrashort pump pulse and an ionizing ultrashort probe pulse it is possible to track the collective dynamics inside the C+ ion in the time domain.