Search

The authors develop and implement experimentally a procedure for quantum-state reconstruction of the complete rotational wave function of a simple molecule. The reconstruction procedure can be adopted without any information on the field-matter interaction to create the rotational wave packet.

A near-infrared laser generates gain on transitions between the $B^{2}\mathrm{\ensuremath{\Sigma}}_{\text{u}}^{+}$ and $X^{2}\mathrm{\ensuremath{\Sigma}}_{\text{g}}^{+}$ states of the nitrogen molecular cation in part by coupling the $X^{2}\mathrm{\ensuremath{\Sigma}}_{\text{g}}^{+}$ and $A^{2}\mathrm{\ensuremath{\Pi}}_{\text{u}}$ states in the $V$ system. Traditional time resolved pump-probe measurements rely on postionization coupling by the pump pulse to initialize dynamics in the $A^{2}\mathrm{\ensuremath{\Pi}}_{\text{u}}$ state. Here we show that a weak second excitation pulse reduces ambiguity because it acts only on the ion independent of ionization. The additional control pulse can increase gain by moving population to the $A^{2}\mathrm{\ensuremath{\Pi}}_{\text{u}}$ state, which modifies the lasing emission in two distinct ways. The presence of fast decoherence on $X^{2}\mathrm{\ensuremath{\Sigma}}_{\text{g}}^{+}$ to $A^{2}\mathrm{\ensuremath{\Pi}}_{\text{u}}$ transitions may prevent the formation of a coherent rotational wave packet in the ground state in our experiment, but the control pulse can reverse impulsive alignment by the pump pulse to remove rotational wave packets in the $B^{2}\mathrm{\ensuremath{\Sigma}}_{\text{u}}^{+}$ state.

In this work, we experimentally study the angle-dependent single ionization of carbon dioxide (CO2) by linearly and circularly polarized pulses. The angle dependence of the ionization probability by linearly polarized pulses extracted from time-domain measurements on an impulsively excited rotational wave packet is compared with data obtained from a direct angle-scan measurement. The results from the measurement with linear and circular polarization are consistent with the adiabatic ionization approximation. We extend the time-domain method to extract the dependence of the asymptotic momentum distribution of fragment ions on the orientation of the molecular axis, and apply it to investigate dissociative double ionization of CO2. We show that such measurements can directly test the validity of the axial recoil approximation.

We simulate the pump-probe experiments of lasing in molecular nitrogen ions with particular interest in the effects of rotational wave-packet dynamics. Our computations demonstrate that the coherent preparation of rotational wave packets in ${\mathrm{N}}_{2}{}^{+}$ by an intense short nonresonant pulse results in a modulation of the subsequent emission from ${B}^{2}\phantom{\rule{0.16em}{0ex}}{\mathrm{\ensuremath{\Sigma}}}_{u}{}^{+}\ensuremath{\rightarrow}{X}^{2}\phantom{\rule{0.16em}{0ex}}{\mathrm{\ensuremath{\Sigma}}}_{g}{}^{+}$ transitions induced by a resonant seed pulse. We model the dynamics of such pumping and emission using density-matrix theory to describe the ${\mathrm{N}}_{2}{}^{+}$ dynamics and the Maxwell wave equation to model the seed pulse propagation. We show that the gain and absorption of a delayed seed pulse is dependent on the pump-seed delay, that is, the rotational coherences excited by the pump pulse can modulate the gain and absorption of the delayed seed pulse. Further, we demonstrate that the coherent rotational dynamics of the nitrogen ions can cause lasing without electronic inversion.

We consider co-rotational wave maps from the ( 1 + d ) -dimensional Minkowski space into the d -sphere for d ≥ 3 odd. This is an energy-supercritical model which is known to exhibit finite-time blowup via self-similar solutions. Based on a method developed by the second author and Schorkhuber, we prove the asymptotic nonlinear stability of the “ground-state” self-similar solution.

Fluence-specified optimal control simulation is applied to C16O/C18O and 14N2/15N2 mixtures to numerically design laser pulses that best achieve isotope-selective alignment. The degree of control is measured in terms of selectivity, which is defined by the difference in the degree of alignment between a heavy isotopologue (HI) and a light isotopologue (LI). Optimal pulses are composed of several subpulses that cooperate with the so-called revivals of the rotational wave packets. Although the two mixtures have slightly different molecular parameters and isotope shifts, it turns out that the optimal pulses share common multi-pulse structures. We also develop a pulse-partitioning analysis to quantitatively and systematically examine the role of inter-subpulse cooperation in the improvement of the isotope-selective alignment. According to the analyses, we find that the ‘coherent’ and the ‘incoherent’ inter-subpulse cooperation almost equally contribute to the improvement of the degree of alignment (HI...

A brief review of theoretical representations and experimental data on rotational motions of elements of a continuous medium is given. Description of wave rotational motions is impossible in the framework of the classical theory of elasticity, but it is allowed within the scope of generalized continua models (the Cosserat microspolar model, moment and gradient models, etc.). The numerical modeling of the parameters of the Cosserat medium is carried out by the structural modeling method, and the ranges of existence of rotational waves are determined for some crystals with cubic symmetry. A new approach to the solution of the problem of rotational motions is offered for the “geological block” continuum, namely, A.V. Vikulin’s model, in which the stresses are described by a symmetric tensor. Geological and geophysical data are presented that confirm both rotational approaches to describing the blocks and plates composing a geomedium, and the existence of rotational waves.

В работе проведено молекулярно-динамическое исследование ротационных полей в изолированном металлическом кристалле наноразмерного масштаба, находящемся при определенной температуре. Показано, что такие поля существуют и при отсутствии внешних механических воздействий. Исследовано влияние температуры и размера наноструктур на удельные вращательные энергии подсистем атомов. В результате статистической обработки численных результатов найдена зависимость удельной вращательной энергии атомов от температуры и размеров структуры., Molecular dynamics investigation is performed on rotational fields in an isolated nanosized metal crystal at a certain temperature. Such fields are shown to exist even without external mechanical action. We investigate how the temperature and size of nanostructures affect specific rotational energies of atom subsystems. Statistical processing of the numerical data is used to find the dependence of the specific rotational energy of atoms on the structure temperature and size.

The paper puts forward a multiscale model of deformed polycrystals according to which the basis for self-consistent deformation of grains is rotational wave flows of planar structural transformations at their boundaries. Computer-aided engineering of grain boundaries reveals two types of rotational wave flows defined by the misorientation angle of adjacent grains. Grain boundary flows of the first type develop at low-angle boundaries and feature low curvature. These flows generate dislocations in the grain bulk and the Hall-Petch equation for them has the form σ=σ0+kd−1/2. Grain boundary flows of the second type develop at high-angle boundaries and feature high curvature. These flows generate curvature bands in near-boundary zones and inject them into the grain bulk, resulting in fragmentation of grains and breakdown of translation invariance. For such self-consistency of grains in a polycrystal, the Hall-Petch equation has the form σ=σ0+kd−1. Experimental data in support of the proposed multiscale model are presented.

Данная статья является частью цикла работ, посвященных изучению возникновения и распространения вихревых структур в твердых телах с помощью метода молекулярной динамики. Дана трактовка этому явлению с точки зрения самоорганизации структуры. Авторами исследовано влияние размера структуры на образование ротационных полей и показано, что их появление не является следствием наноразмерной малости образца. При этом показано влияние поперечного размера наноструктуры на энергию ротационного поля., This paper continues a series of studies on the formation and development of vortex structures in solids using the molecular dynamic method. This phenomenon is interpreted from the viewpoint of structural self-organization. The effect of the structure size on the formation of rotational fields has been studied to show that their appearance is not a consequence of the specimen nanosize. It is shown that the lateral nanostructure size influences the rotational field energy.

Spatiotemporal behaviors of the shear band have been analyzed. Based on a recent field theory of deformation and fracture, it has been hypothesized that (a) a shear band is formed along the boundary of opposite rotational displacements of a specimen. (b) When the propagation velocity of movable dislocations along the front of a shear band is higher than the phase velocity of the rotation wave the shear band appears continuously whereas when the velocity of the dislocations is lower than the rotation wave the shear band travels at the same velocity as the rotational wave appearing intermittently. Electronic-Speckle-Pattern Interferometric setup has been used to monitor the formation and movement of shear bands under various tensile strain rates. The observed spatiotemporal characteristics of the shear bands have been found to support the above hypotheses.

The rotation of molecules in the gas phase can be coherently excited by irradiation with strong nonresonant short laser pulses, interacting with the molecular anisotropic polarisability. Such coherent rotational excitation has been attracting much attention because of the intriguing nature of the rotational wave packet thus created, and its wide applicability to dynamical studies and advanced optics. In this review article, we first survey various experimental schemes adopted so far for externally controlling molecular rotation, and then describe a new approach based on a quantum-state resolved spectroscopic probe for investigating coherent rotational excitation by intense nonresonant laser fields. Representative examples are given to show how the method provides detailed information on excitation pathways in wave-packet creation, and how it realises full quantum-state reconstruction of the rotational wave packet in a favourable case. We also describe an advanced wave-packet control, i.e. the creation and...

We study the rotational wave packet created by nonadiabatic rotational excitation of molecules with strong femtosecond laser pulses. The applicable condition of the Delta-Kick method is obtained by comparing the laser intensity and pulse duration dependences of the wave packet calculated with different methods. The wave packet evolution is traced analytically with the Delta-Kick method. The calculations demonstrate that the rotational populations can be controlled for the rotational wave packet created by two femtosecond laser pulses. The evolution of the rotational wave packet with controlled populations produces interference patterns with exotic spatial symmetries. These calculations are validated by comparing the theoretical calculations with our experimental measurements for the rotational wave packet created by thermal ensemble CO(2) and two strong femtosecond laser pulses. Potential applications in molecular science are also discussed for the rotational wave packet with controlled populations and spatial symmetries.

An outstanding event in the development of the classical mechanics of continuous media was publication in 1909 of the book of French researchers—brothers Eugene and Francois Cosserat “Theorie des Corps Deformables” (The theory of deformable solids) [85] that laid the foundations of the mechanics of generalized continua.

The mixing performance of reciprocal shake mixing was extremely different from that of rotationally shake mixing. The mixing time did not decrease monotonously with increasing the shaking frequency. The transition of a flow pattern from a progressive wave type to a rotational wave type was quite complicated. The frequency, at which the steady rotational flow gives the optimum operation for mixing, is directly proportional to the natural frequency of the cylindrical vessel. This frequency can also be correlated only with the Froude number, and it did not depend on the shaking width. The mixing time decreased monotonously with increasing the power consumption per unit volume.

The chemical and physical properties of molecular clusters can heavily depend on their size, which makes them very attractive for the design of new materials with tailored properties. Deriving the structure and dynamics of clusters is therefore of major interest in science. Weakly bound clusters can be studied using conventional spectroscopic techniques, but the number of lines observed is often too small for a comprehensive structural analysis. Impulsive alignment generates rotational wavepackets, which provides simultaneous information on structure and dynamics, as has been demonstrated successfully for isolated molecules. Here, we apply this technique for the firsttime to clusters comprising of a molecule and a single helium atom. By forcing the population of high rotational levels in intense laser fields we demonstrate the generation of rich rotational line spectra for this system, establishing the highly delocalised structure and the coherence of rotational wavepacket propagation. Our findings enable studies of clusters of different sizes and complexity as well as incipient superfluidity effects using wavepacket methods., 5 pages, 6 figures

We show, by computation and experiment, that a sequence of nonresonant and impulsive laser pulses with different ellipticities can effectively align asymmetric top molecules in three dimensions under field-free conditions. By solving the Schr\"odinger equation for the evolution of the rotational wave packet, we show that the 3D alignment of 3,5 difluoroiodobenzene molecules improves with each successive pulse. Experimentally, a sequence of three pulses is used to demonstrate these results, which extend the multipulse schemes used for 1D alignment to full 3D control of rotational motion.

We experimentally reconstructed a rotational wave packet created in NO(X2Π1/2) by a nonresonant intense ultrashort laser field. The determined phase shifts show a clear signature of bifurcated pathways in the nonadiabatic rotational excitation.

В рамках метода молекулярной динамики был рассчитан процесс формирования кластерной структуры, границ раздела и поверхностей с различными радиусами кривизны при прохождении нелинейной волны по идеальному нанокристаллу. Показано, что этот процесс является формой самоорганизации наноструктуры при воздействии потока внешней энергии с последующим развитием интенсивного ротационного поля., Molecular dynamics simulation was performed to study the formation of cluster structure, interfaces, and surfaces differing in curvature radius in a perfect nanocrystal when passed through by a nonlinear wave. It is shown that this process is a type of nanostructure self-organization in response to external energy flow with subsequent development of a strong rotational field.

This research is a contribution to the study of the propagation of elastic waves in granular media. The main purpose is to analyze two particular aspects that influence the propagation, first the rotation motion of grain and other nonlinearities of contact. As part of this work, the periodic one-dimensional granular structure is studied. The main contribution of this work is the experimental demonstration and modeling purely rotational wave in a granular chain composed of magnetic beads. The starting point of modeling is the description of the pure shear coupling at the contact between two spheres excited in torsion up to the first order of nonlinearity. For a oscillating torque, pure nonlinear quadratic hysteretic behaviour is shown. Generally, this nonlinearity coexists with other types of nonlinearities (quadratic, clapping, ...) and some of its effects have not been observed. For the first time, the transformation of pulse profile in a medium with pure hysteretic quadratic nonlinearity, essentially different from the distortion by classical nonlinearities, is reported.Other effects related to the dispersion and nonlinearity of contact in a diatomic chain are studied theoretically and experimentally. In particular, the generation of the 2nd harmonic wave compression presents an interesting behaviour according to their propagating nature, highly dispersive or evanescent. Apart from the fundamental interests, the results may find applications in the field of wave control: amplitude dependent filtering devices, rectifiers, actuating devices, acoustic diodes, ... ., Ce travail de recherche est une contribution à l'étude de la propagation d'ondes élastiques dans les milieux granulaires. L'objectif principal est d'analyser deux aspects particuliers qui influencent la propagation, d'une part le degré de liberté en rotation des grains et d'autre part les non-linéarités de contact. Dans le cadre de ce travail, des structures granulaires périodiques et unidimensionnelles sont étudiées.L'apport principal de ce travail est la mise en évidence expérimentale et la modélisation d'ondes de rotation pures dans une chaîne granulaire composée de billes magnétiques. Le point de départ de la modélisation est la description du contact en torsion entre deux sphères jusqu'au premier ordre de non-linéarité. Pour un moment de torsion oscillant, il est montré un comportement de type purement hystérétique quadratique. Généralement, cette non-linéarité coexiste avec d'autres types de non-linéarités (quadratique, clappement, ...) et certains de ses effets n'ont jamais été observés. Pour la première fois, la distorsion d'ondes impulsionnelles par une non-linéarité hystérétique est mise en évidence et modélisée.D'autres effets liés à la dispersion et aux non-linéarités de contact dans une chaîne diatomique sont étudiés théoriquement et expérimentalement. En particulier, la génération de l'harmonique 2 des ondes de compression présente une richesse intéressante selon leur caractère propagatif, fortement dispersif ou évanescent.Outre les apports fondamentaux, les résultats obtenus peuvent trouver des applications dans le domaine du contrôle des ondes : filtres acoustiques dépendant de l'amplitude, convertisseurs de fréquences, rectificateurs et diodes acoustiques, ... .

Complex revival features of rotational wave packets are obtained from the interplay of a molecular rotational distribution and a measured physical observable. The analysis of the measured temporal behavior can be used to retrieve either one or both quantities. We show here the first observation of high order fractional revival (up to 1/12 in CO2) using time-of-flight measurements of ion yields leading to the information required for full reconstruction of the rotational wave packet. We further show via an analysis of higher order fractional revivals in high harmonic generation that new information on the participating ionic channels can be clearly identified, showing the general implication of our results.

The revival structure of strong-field-induced rotational wave packets differs qualitatively from revival structures analyzed in the past. One of the consequences of this difference is strong enhancement of the alignment of such wave packets after turn-off of the laser pulse, under field-free conditions.

In this paper, a theoretical model is proposed to investigate the molecular rotational state populations pumped by multiple laser pulses through an impulsive Raman process based on second-order perturbation theory and an analytical solution for the dependence of the rotational state populations on the time delays and the relative amplitudes of the multiple laser pulses has been achieved. The results indicate that the molecular rotational state populations can be controlled by precisely manipulating the time delays and the relative amplitudes, which can be significantly enhanced or completely suppressed, and so the molecular rotational wave packet and field-free molecular alignment can be efficiently manipulated.

We show that high harmonic generation is the most sensitive probe of rotational wave packet revivals, revealing very high-order rotational revivals for the first time using any probe. By fitting high-quality experimental data to an exact theory of high harmonic generation from aligned molecules, we can extract the underlying electronic dipole elements for high harmonic emission and uncover that the electron gains angular momentum from the photon field.

We exhibit stable finite time blow up regimes for the energy critical co-rotational Wave Map with the S 2 target in all homotopy classes and for the critical equivariant SO(4) Yang-Mills problem. We derive sharp asymptotics on the dynamics at blow up time and prove quantization of the energy focused at the singularity.

We demonstrate the measurement of field-free molecular alignment of air can be realized by combining the weak field polarization technique (WFPT) with a balanced detection system. The measured signal is proportional to the alignment parameter. Periodic revival structures of the transient alignment and permanent alignment between revivals can be detected clearly by a single measurement with high sensitivity. Fourier transform spectrum of the measured signal agrees well with the calculation result and provides information of the populations of different J states in the rotational wave packet.

Experiments on THz pulse generation from single and multiple filaments in air using single or two-color technique will be discussed. Its application to sensing molecular rotational wave packet revival will be given. Stand-off detection of THz from a distance through monitoring nitrogen fluorescence in a filament was observed. The physics seems to be due to population trapping in the wake of strong field interaction with nitrogen molecules inside the filament. Article not available.

The existence of co-rotational finite time blow up solutions to the wave map problem from \({\mathbb{R}^{2+1} \to N}\) , where N is a surface of revolution with metric dρ2 + g(ρ)2dθ2, g an entire function, is proven. These are of the form \({u(t,r)=Q(\lambda(t)t)+\mathcal{R}(t,r)}\) , where Q is a time independent solution of the co-rotational wave map equation −utt + urr + r−1ur = r−2g(u)g′(u), λ(t) = t−1-ν, ν > 1/2 is arbitrary, and \({\mathcal{R}}\) is a term whose local energy goes to zero as t → 0.

We observe rotational wave packet dynamics in CO2 through third harmonic generation (THG). The conversion efficiency of THG is modulated by the wavepacket through ultrafast perturbations to linear and third-order optical susceptibilities.