Transient Wave Packets Research Articles

Coherent transient exciton transport in disordered polaritonic wires

Abstract Excitation energy transport can be significantly enhanced by strong light–matter interactions. In the present work, we explore intriguing features of coherent transient exciton wave packet dynamics on a lossless disordered polaritonic wire. Our main results can be understood in terms of the effective exciton group velocity, a new quantity we obtain from the polariton dispersion. Under weak and moderate disorder, we find that the early wave packet spread velocity is controlled by the overlap of the initial exciton momentum distribution and its effective group velocity. Conversely, when disorder is stronger, the initial state is nearly irrelevant, and red-shifted cavities support excitons with greater mobility. Our findings provide guiding principles for optimizing ultrafast coherent exciton transport based on the magnitude of disorder and the polariton dispersion. The presented perspectives may be valuable for understanding and designing new polaritonic platforms for enhanced exciton energy transport.

What caused the unseasonal extreme dust storm in Uzbekistan during November 2021?

An unseasonal dust storm hit large parts of Central Asia on 4–5 November 2021, setting records for the column aerosol burden and fine particulate concentration in Tashkent, Uzbekistan. The dust event originated from an agropastoral region in southern Kazakhstan, where the soil erodibility was enhanced by a prolonged agricultural drought resulting from La Niña-related precipitation deficit and persistent high atmospheric evaporative demand. The dust outbreak was triggered by sustained postfrontal northerly winds during an extreme cold air outbreak. The cold air and dust outbreaks were preceded by a chain of processes consisting of recurrent synoptic-scale transient Rossby wave packets over the North Pacific and North Atlantic, upper-level wave breaking and blocking over Greenland, followed by high-latitude blocking over Northern Europe and West Siberia, and the equatorward shift of a tropopause polar vortex and cold pool into southern Kazakhstan. Our study suggests that the historic dust storm in Uzbekistan was a compound weather event driven by cold extreme, high winds, and drought precondition.

Experimental Study on the Effect of Extreme Waves on a LNG Carrier

This paper presents a comprehensive experimental study on the effect of extreme waves on a LNG carrier. The LNG carrier model was equipped with a variety of sensors to measure motions, green water height on deck as well as local and global loads. Experiments in transient wave packets provided the general performance in waves in terms of response amplitude operators and were accompanied by tests in regular waves with two different wave steepness. These tests allowed detailed insights into the nonlinear behavior of the vertical wave bending moment in steep waves showing that green water on deck can contribute to a decrease of vertical wave bending moment. Afterwards, systematic model tests in irregular waves were performed to provide the basis for statistical analysis. It is shown that the generalized extreme value distribution model is suitable for the estimation of the extreme peak values of motions and loads. Finally, model tests in tailored extreme wave sequences were conducted comparing the results with the statistical analysis. For this purpose, analytical breather solutions of the nonlinear Schrödinger equation were applied to generate tailored extreme waves of certain critical wave lengths in terms of ship response. Besides these design extreme waves, the LGN carrier was also investigated in the model scale reproduction of the real-world Draupner wave. By comparing the motions, vertical wave bending moment, green water column and slamming pressures it is concluded that the breather solutions are a powerful and efficient tool for the generation of design extreme waves of certain critical wave lengths for wave/structure investigations on different subjects.

Note on the Application of Transient Wave Packets for Wave–Ice Interaction Experiments

This paper presents the transient wave packet (TWP) technique as an efficient method for wave–ice interaction experiments. TWPs are deterministic wave groups, where both the amplitude spectrum and the associated phases are tailor-made and manipulated, being well established for efficient wave–structure interaction experiments. One major benefit of TWPs is the possibility to determine the response amplitude operator (RAO) of a structure in a single test run compared to the classical approach by investigating regular waves of different wave lengths. Thus, applying TWPs for wave–ice interaction offers the determination of the RAO of the ice at specific locations. In this context, the determination of RAO means that the ice characteristics in terms of wave damping over a wide frequency range are obtained. Besides this, the wave dispersion of the underlying wave components of the TWP can be additionally investigated between the specific locations with the same single test run. For the purpose of this study, experiments in an ice tank, capable of generating tailored waves, were performed with a solid ice sheet. Besides the generation of one TWP, regular waves of different wave lengths were generated as a reference to validate the TWP results for specific wave periods. It is shown that the TWP technique is not only applicable for wave–ice interaction investigations, but is also an efficient alternative to investigations with regular waves.

Taking snapshots of a moving electron wave packet in molecules using photoelectron holography in strong-field tunneling ionization* *Project supported by the National Natural Science Foundation of China (Grant Nos. 11874163, 11604108, and 11604388), the Program for HUST Academic Frontier Youth Team, and the Fundamental Research Funds for the Central Universities, China (HUST No. 2017KFXKJC002).

Coherent superposition of electronic states induces attosecond electron motion in molecules. We theoretically investigate the strong-field ionization of this superposition state by numerically solving the time-dependent Schrödinger equation. In the obtained photoelectron momentum distribution, an intriguing bifurcation structure appears in the strong-field holographic interference pattern. We demonstrate that this bifurcation structure directly provides complete information about the status of the transient wave function of the superposition state: the horizontal location of the bifurcation in the momentum distribution reveals the relative phase of the involved components of the superposition state and the vertical position indicates the relative coefficient. Thus, this bifurcation structure takes a snapshot of the transient electron wave packet of the superposition state and provides an intuitive way to monitor electron motion in molecules.

Recurrent Rossby Wave Packets Modulate the Persistence of Dry and Wet Spells Across the Globe

AbstractPersistent dry and wet spells can arise from stationary weather situations or recurrent flow patterns and result in significant socio‐economic impacts. Here, we study the effects of recurrent synoptic‐scale transient Rossby wave packets (RRWPs) on the persistence of dry and wet spells using the ERA‐Interim reanalysis data. RRWPs significantly alter (decrease and increase) dry and wet spell persistence across the globe. Spatial patterns of statistically significant links between RRWPs and spell durations arise from the superposition of a zonally symmetric component and a wave‐like component that is modulated by local factors such as orography and the position relative to major moisture sources. The zonally symmetric component is apparent during the Northern Hemisphere winter and dominates the Southern Hemisphere signal in winter and summer. The wave‐like component appears primarily in the Northern Hemisphere, changes its wavenumber with the season and is thus, conceivably related to stationary wave dynamics.

Visualizing conical intersection passages via vibronic coherence maps generated by stimulated ultrafast X-ray Raman signals

The rates and outcomes of virtually all photophysical and photochemical processes are determined by conical intersections. These are regions of degeneracy between electronic states on the nuclear landscape of molecules where electrons and nuclei evolve on comparable timescales and thus become strongly coupled, enabling radiationless relaxation channels upon optical excitation. Due to their ultrafast nature and vast complexity, monitoring conical intersections experimentally is an open challenge. We present a simulation study on the ultrafast photorelaxation of uracil, based on a quantum description of the nuclei. We demonstrate an additional window into conical intersections obtained by recording the transient wavepacket coherence during this passage with an X-ray free-electron laser pulse. Two major findings are reported. First, we find that the vibronic coherence at the conical intersection lives for several hundred femtoseconds and can be measured during this entire time. Second, the time-dependent energy-splitting landscape of the participating vibrational and electronic states is directly extracted from Wigner spectrograms of the signal. These offer a physical picture of the quantum conical intersection pathways through visualizing their transient vibronic coherence distributions. The path of a nuclear wavepacket in the vicinity of the conical intersection is directly mapped by the proposed experiment.

Recurrent Synoptic-Scale Rossby Wave Patterns and Their Effect on the Persistence of Cold and Hot Spells

AbstractThe persistence of surface weather during several recent high-impact weather events has been pivotal in generating their societal impact. Here we examine Hovmöller diagrams of the 250-hPa meridional wind during several periods with particularly persistent surface weather and find a common pattern in these Hovmöller diagrams. This pattern can be characterized as a “recurrent Rossby wave pattern” (RRWP), arising from multiple transient synoptic-scale wave packets. During such RRWP periods, individual troughs and ridges forming the wave packets repeatedly amplify in the same geographical region. We discuss the synoptic evolution of two RRWP periods, in February–March 1987 and July–August 1994, and illustrate how the recurrence of the transient wave packets led to unusually long-lasting cold and hot spells, which occurred simultaneously in several regions, each separated by roughly one synoptic wavelength. Furthermore, a simple index termedRis proposed to identify RRWPs, which is based on both a time and wavenumber filter applied to conventional Hovmöller diagrams. A Weibull regression analysis then shows that large values ofRare statistically significantly linked to increased durations of winter cold and summer hot spells in large areas of the Northern Hemisphere midlatitudes. Traditionally, persistent high-impact surface weather has often been linked to the occurrence of proximate atmospheric blocking. In contrast to blocking, RRWPs affect persistent surface temperature anomalies over multiple synoptic wavelengths. We therefore argue that, in addition to blocking, RRWPs should be considered as an important flow feature leading to persistent high-impact surface weather.

Extreme Wave Generation, Breaking, and Impact Simulations Using Wave Packets in REEF3D

On several occasions, freak waves have been observed in the past, some causing severe damage. In order to model such extreme wave conditions, one possibility is to use focused waves of first- or second-order based on irregular sea-state wave spectra. The wave phase is chosen such that the waves focus at a predetermined location and time, but the individual wave components become steep and start breaking before the focus location for large amplitudes. In this study, transient wave packets are used for extreme wave generation. Extreme waves are generated that are higher and only break at the concentration point using the transient wave packets method implemented in the open-source CFD model REEF3D. Model validation is performed by comparison to experimental results. The generation of wave packets with an 8.3 times shorter focus distance is investigated and the wave is replicated in a shorter domain with a 9% higher crest. The method is further used to generate a steepness induced-breaking wave and calculation of extreme wave forces on an offshore structure is demonstrated.

Linking Northern Hemisphere temperature extremes to Rossby wave packets

This work investigates the statistical linkage between upper‐tropospheric transient Rossby wave packets (RWPs) and lower‐tropospheric temperature extremes in the Northern Hemisphere during the period 1979–2015. Data from ERA‐Interim reanalyses are used for the diagnosis of RWP amplitude and temperature anomalies as well as the systematic examination of their connection. Areas of large RWP amplitude are found to be associated with an increased probability of lower‐tropospheric temperature extremes in many regions of the midlatitudes. Although a seasonal and inter‐regional variability is apparent, this link is always stronger than in an analysis using a circumglobal waviness metric based on Fourier wavenumber amplitudes.Further insight is gained by complementing the climatological results with an investigation of the two most severe recent heat waves in Europe, viz. during the 2003 and 2010 summers. Both events are found to be associated with conspicuous non‐circumglobal RWPs, but differences between the two events suggest that the mechanisms linking RWPs and temperature extremes are case‐dependent. The aforementioned results underscore the important role of upper‐troposphere dynamics and open up avenues for future research on heat waves and cold spells at both weather and climate time‐scales.

Southern Hemisphere summertime Rossby waves and weather in the Australian region

Motivated by recent studies on the significant summertime weather patterns in the Australian region, the life cycle of summertime transient Rossby wave packets in the Southern Hemisphere is investigated. The strength of the interaction I between the wave packets and the jet is defined by the advection of potential vorticity by the divergent part of the wind on the 350 K isentropic surface. The magnitude of I is used as the basis for time‐lagged composites in distinct regions: southwest Chile, southwest Africa, over the Indian Ocean, southwest Australia, and over the West Pacific. The interaction is strongest on the stratospheric side of the jet core. Although in each case cyclogenesis from a pre‐existing disturbance in the upper troposphere precedes the generation of the Rossby wave packets, there are two types of interaction with the jet. In the souhwest Chile, southwest Africa and Indian Ocean cases, extratropical cyclogenesis and the associated convection lies on the poleward side of the jet, and hence I is positive. In the southwest Australia and West Pacific cases, extratropical cyclogenesis occurs 3 days earlier than the others, and I is negative as it describes the interaction of a downstream propagating Rossby wave packet with the subtropical jet. In all cases, as the cyclones develop, the wave activity propagates from low levels to the upper levels of the troposphere, and then downstream and equatorwards towards higher values of refractive index. The equatorward refraction of the southwest Australia and West Pacific wave packets is accompanied by enhanced tropical convection in the warm conveyor belt of the advancing front.

The breaking of transient inertio-gravity waves in a shear flow using the Gaussian beam approximation

AbstractThe propagation of transient inertio-gravity waves in a shear flow is examined using the Gaussian beam formulation. This formulation assumes Gaussian wavepackets in the spectral space and uses a second-order Taylor expansion of the phase of the wave field. In this sense, the Gaussian beam formulation is also an asymptotic approximation like spatial ray tracing; however, the first one is free of the singularities found in spatial ray tracing at caustics. Therefore, the Gaussian beam formulation permits the examination of the evolution of transient inertio-gravity wavepackets from the initial time up to the destabilization of the flow close to the critical levels. We show that the transience favours the development of the dynamical instability relative to the convective instability. In particular, there is a well-defined threshold for which small initial amplitude transient inertio-gravity waves never reach the convective instability criterion. This threshold does not exist for steady-state inertio-gravity waves for which the wave amplitude increases indefinitely towards the critical level. The Gaussian beam formulation is shown to be a powerful tool to treat analytically several aspects of inertio-gravity waves in simple shear flows. In more realistic shear flows, its numerical implementation is readily available and the required numerical calculations have a low computational cost.

Global stability and optimal perturbation for a jet in cross-flow

We study the stability of a jet in cross-flow at low values of the jet to cross-flow velocity ratio R using direct numerical simulations (DNS) and global linear stability analysis adopting a time-stepper method. For the simplified setup without a meshed pipe in the simulations we compare results of a fully-spectral code SIMSON with a spectral-element code Nek5000. We find the use of periodic domains, even with the fringe method, unsuitable due to the large sensitivity of the eigenvalues and due to the large spatial growth of the corresponding eigenmodes. However, we observe a similar sensitivity to reflection from the outflow boundary in the inflow/outflow configuration, and therefore we use an extended domain where reflections are minimal. We apply in our studies both modal and non-modal linear analyses investigating transient effects and their asymptotic fate, and we find a transient wavepacket to develop almost identically in both the globally stable and unstable cases. The final results of the global stability analysis for our numerical setup show the critical value of R, at which the first bifurcation occurs, to lie in the range between 1.5 and 1.6.

The propagation of transient wave packets in highly dissipative media

AbstractThe group velocity of a wave packet is defined in terms of the central wave number. Because of scale‐dependent dissipation, the central wave number migrates to lower values as transient wave packets propagate through dissipative media. The importance of this effect is greater the broader the bandwidth of the wave packet is or the more localized it is spatially. For modest localization, the migration of the central wave number significantly accelerates the vertical motion of wave packets and allows propagation to significantly greater altitudes before packets are substantially dissipated. Wave packets may experience significant attenuation due to dispersion before they begin to experience strong viscous dissipation.

Anomalous wave propagation in a one-dimensional acoustic metamaterial having simultaneously negative mass density and Young’s modulus

A mechanical model representing an acoustic metamaterial that exhibits simultaneously negative mass density and negative Young's modulus was proposed. Wave propagation was studied in the frequency range of double negativity. In view of positive energy flow, it was found that the phase velocity in this range is negative. This phenomenon was also observed using transient wave propagation finite-element analyses of a transient sinusoidal wave and a transient wave packet. In contrast to wave propagation in the region of positive mass and modulus, the peculiar backward wave motion in the region of double negativity was clearly displayed.

Real-Time Observation of Interference between Atomic One-Electron and Two-Electron Excitations

We present results of real-time tracking of atomic two-electron dynamics in an autoionizing transient wave packet in krypton. A coherent superposition of two Fano resonances is excited with a femtosecond extreme-ultraviolet pulse. The evolution of the corresponding wave packet is subsequently probed with a delayed infrared pulse. In our specific case, we get access to the interference between one- and two-electron excitation channels in the launched wave packet, which is superimposed on its decay through autoionization. A simple model is able to account for the observed dynamical evolution of this wave packet.

On the transient responses of floating beams and the role of radiation damping

The paper investigates the free vibration behaviour of a floating beam and its forced responses to transient wave packets. The analysis is based on the well-known simple model of a uniform Euler–Bernoulli beam, in which the coupled hydroelastic problem is solved directly. In principle the formulation is exact, within the context of linear theory and potential flow. The problem is discretised and complex eigenvalues of the system matrix are evaluated, in order to characterise the free vibration behaviour (the natural frequencies and radiation damping) over a range of dimensionless beam stiffnesses and mass ratios. The magnitudes of ‘resonant’ responses are shown to be linked to the imaginary parts of these eigenvalues. The model is then used to study the responses of the flexible beam in transient wave packets, such as the NewWave group.

Dipole-Resonance Assisted Isomerization in the Electronic Ground State Using Few-Cycle Infrared Pulses

A computational investigation of HCN → HNC isomerization in the electronic ground state by one- and few-cycle infrared pulses is presented. Starting from a vibrationally pre-excited reagent state, isomerization yields of more than 50% are obtained using single one- to five-cycle pulses. The principal mechanism includes two steps of population transfer by dipole-resonance (DR), and hence, the success of the method is closely linked to the polarity of the system and, in particular, the stepwise change of the dipole moment from reactant to transition state and on to products. The yield drops massively if the diagonal dipole matrix elements are artificially set to zero. In detail, the mechanism includes DR-induced preparation of a delocalized vibrational wavepacket, which traverses the barrier region and is finally trapped in the product well by DR-dominated de-excitation. The excitation and de-excitation steps are triggered by pulse lobes of opposite field direction. As the number of optical cycles is increased, the leading field lobes prepare a vibrational superposition state by off-resonant ladder climbing, which is then subjected to the three steps of the principal isomerization mechanism. DR excitation is more efficient from a preformed vibrational wavepacket than from a molecular eigenstate. The entire process can be loosely described as Tannor-Kosloff-Rice type transfer mechanism on a single potential surface effected by a single pulse, individual field lobes assuming the roles of pump- and dump-pulses. Pre-excitation to a transient wavepacket can be enhanced by applying a separate, comparatively weak few-cycle prepulse, in which the prepulse prepares a vibrational wavepacket. The two-pulse setup corresponds to a double Tannor-Kosloff-Rice control scheme on a single potential surface.

BREAKING CRITERIA FOR LABORATORY EXPERIMENTS BASED ON THE PHASE-TIME-METHOD (PTM)

Breaking waves generated by focusing of transient wave packets have been analyzed. By a comparison of video data and gauge measurements the threshold frequency for the use of the PTM as a breaking criterion is derived. The present result is slightly higher than the original value of Zimmermann & Seymour (2002) for spilling breakers, but confirms the results of Irschik & Oumeraci (2006). Additionally the use of the zero down-cross period Tz instead of the peak period TP is investigated. Both definitions lead for the present conditions with plunging breakers to almost identical results.

Control of coherent excitation of neon in the extreme ultraviolet regime

Coherent excitation of a superposition of Rydberg states in neon by the 13th harmonic of an intense 804 nm pulse and the formation of a wave packet is reported. Pump-probe experiments are performed, where the 3d-manifold of the 2p6-->2p5 (2P3/2) 3d [1/2]1- and 2p6-->2p5 (2P3/2) 3d [3/2]1-transitions are excited by an extreme ultraviolet (XUV) radiation pulse, which is centered at 20.05 eV photon energy. The temporal evolution of the excited state population is probed by ionization with a time-delayed 804 nm pulse. Control of coherent transient excitation and wave packet dynamics in the XUV-regime is demonstrated, where the spectral phase of the 13th harmonic is used as a control parameter. Modulation of the phase is achieved by propagation of the XUV-pulse through neon of variable gas density. The experimental results indicate that phase-shaped high-order harmonics can be used to control fundamental coherent excitation processes in the XUV-regime.