High-intensity Laser Field Research Articles

New exact solutions of the Dirac equation of a charged particle interacting with an electromagnetic plane wave in a medium

Exact solutions are presented of the Dirac equation of a charged particle moving in a classical monochromatic electromagnetic plane wave in a medium of index of refraction nm < 1. The found solutions are expressed in terms of new complex trigonometric polynomials, which form a doubly infinite set labelled by two integer quantum numbers. These quantum numbers represent quantized spectra of the energy–momentum components of the charged particle along the polarization vector and along the propagation direction of the applied electromagnetic plane wave field (which is considered as a laser field of arbitrarily high intensity propagating in an underdense plasma). The found solutions may serve as a basis for the description of possible quantum features of mechanisms for the acceleration of electrons by high-intensity laser fields.

Dynamics of ultra-intense circularly polarized solitons under inhomogeneous plasmas

The dynamics of the ultra-intense circularly polarized solitons under inhomogeneous plasmas are examined. The interaction is modeled by the Maxwell and relativistic hydrodynamic equations and is solved with fully implicit energy-conserving numerical scheme. The soliton is self-consistently generated by the interaction between laser and plasma on the vacuum-plasma interface, and the generation mechanism is well confirmed by two dimensional particle-in-cell simulation. It is shown that a propagating weak soliton can be decreased and reflected by increasing plasma background, which is consistent with the existing studies based on hypothesis of weak density response. However, it is found that ultra-intense soliton is well trapped and kept still when encountering increasing background. Probably, this founding can be applied for trapping and amplifying high-intensity laser-fields.

The Influence of Strong Laser Fields on the Interaction between Fast B+3 Clusters and Plasmas

The influence of a high-intensity laser field on the inelastic interactions between a swift B+3 cluster ion and a plasma target is studied by means of the linearized Vlasov-Poisson theory. Excitations of the plasma are described by the classical plasma dielectric function. In the presence of the laser field, the general expressions for the induced potential in the target and the interaction force among the ions within the cluster are derived. Based on the numerical solution of the equations of motion for the constituent ions, the Coulomb explosion patterns and the cluster's energy losses are discussed for a range of laser parameters.

Relativistic Ponderomotive Force Including Higher Order Nonlocal Effects in High Intensity Laser Fields

Relativistic Ponderomotive Force Including Higher Order Nonlocal Effects in High Intensity Laser Fields

Nonlocal properties of ponderomotive force in strongly nonuniform high intensity laser fields

In order to study the particle dynamics in strongly nonuniform and/or localized laser fields, we extend the theory of the ponderomotive force by taking into account the laser field structure up to the higher order with respect to � , the ratio between the particle excursion length and the scale length of the laser field amplitude variation. This extension is realized by keeping the rigorous phase space Lagrangian structure utilizing the noncanonical Lie perturbation up to higher orders. As a result, the equations of motion in a oscillation center coordinate is derived up to the third order of � , which include the second and third spatial derivatives of the laser field amplitude. This denotes that the ponderomotive force depends not only on the local field gradient, but also on the curvature and its derivative. The additional higher-order force originates from the nonlocal particle motion around the oscillation center, which could have an influence especially in the case of tight focusing in the level of laser wavelength.

FUNDAMENTAL PHYSICS EXPLORED WITH HIGH INTENSITY LASER

Over the last century the method of particle acceleration to high energies has become the prime approach to explore the fundamental nature of matter in laboratory. It appears that the latest search of the contemporary accelerator based on the colliders shows a sign of saturation (or at least a slow-down) in increasing its energy and other necessary parameters to extend this frontier. We suggest two pronged approach enabled by the recent progress in high intensity lasers. First we envision the laser-driven plasma accelerator may be able to extend the reach of the collider. For this approach to bear fruit, we need to develop the technology of high averaged power laser in addition to the high intensity. For this we mention that the latest research effort of ICAN is an encouraging sign. In addition to this, we now introduce the concept of the noncollider paradigm in exploring fundamental physics with high intensity (and large energy) lasers. One of the examples we mention is the laser wakefield acceleration (LWFA) far beyond TeV without large luminosity. If we relax or do not require the large luminosity necessary for colliders, but solely in ultrahigh energy frontier, we are still capable of exploring such a fundamental issue. Given such a high energetic particle source and high-intensity laser fields simultaneously, we expect to be able to access new aspects on the matter and the vacuum structure from fundamental physical point of views. LWFA naturally exploits the nonlinear optical effects in the plasma when it becomes of relativistic intensity. Normally nonlinear optical effects are discussed based upon polarization susceptibility of matter to external fields. We suggest application of this concept even to the vacuum structure as a new kind of order parameter to discuss vacuum-originating phenomena at semimacroscopic scales. This viewpoint unifies the following observables with the unprecedented experimental environment we envision; the dispersion relation of photons at extremely short wavelengths in vacuum (a test of the Lorentz invariance), the dispersion relation of the vacuum under high-intensity laser fields (nonperturbative QED and possibly QCD effects), and wave-mixing processes possibly caused by exchanges of low-mass and weakly coupling fields relevant to cosmology with the coherent nature of high-flux photons (search for light dark matter and dark energy). These observables based on polarization susceptibility of vacuum would add novel insights to phenomena discovered in cosmology and particle physics where order parameters such as curvature and particle masses are conventionally discussed. In other words the introduction of high intensity laser and its methodology enriches the approach of fundamental and particle physics in entirely new dimensions.

Influence of a strong laser field on the Coulomb explosion and the stopping power of fast C60clusters in plasmas

The influence of a high-intensity laser field on the Coulomb explosion and stopping power for a swift C${}_{60}$ cluster ion in a plasma target is studied by means of the molecular dynamics method based on the linearized Vlasov-Poisson theory. In the presence of the laser field, the general expressions for the induced potential in the target among the ions within the cluster are derived. Based on the numerical solution of the equations of motion for the constituent ions, the Coulomb explosion patterns and the cluster's stopping power are discussed for a range of laser and plasma parameters. Numerical results show that the laser field affects the correlation between the ions and contributes to weakening the wake effect and the stopping power as compared to the laser-free case. On the other hand, the vicinage effects in the cluster Coulomb explosion dynamics and the stopping power are strongly affected by the variations in the laser parameters, cluster speed, and plasma parameters. For example, Coulomb explosions are found to be hindered in the longitudinal expansion with the increasing of laser intensity and laser angle, and the Coulomb explosions proceed faster for lower plasma densities and higher electron temperatures.

Influence of a strong laser field on Coulomb explosion and stopping power of energetic H3+ clusters in plasmas

The influence of a high-intensity laser field on the Coulomb explosion and stopping power for a swift H3+ cluster ion in a plasma target is studied by means of the molecular dynamic (MD) method based on the linearized Vlasov–Poisson theory. Excitations of the plasma are described by the classical plasma dielectric function. In the presence of the laser field, the general expressions for the induced potential in the target and the interaction force among the ions within the cluster are derived. Based on the numerical solution of the equations of motion for the constituent ions, the Coulomb explosion patterns and the cluster's stopping power are discussed for a range of laser parameters. Numerical results show that the laser field affects the correlation between the ions and contributes to weaken the wake effect and the stopping power as compared to the laser-free case. On the other hand, the stopping power ratio of H3+ cluster is higher than the situation of dicluster of H2+ due to the vicinage effect in the cluster.

Increase of SERS Signal upon Heating or Exposure to a High-Intensity Laser Field: Benzenethiol on an AgFON Substrate

The surface-enhanced Raman scattering (SERS) signal from an AgFON plasmonic substrate, recoated with benzenethiol, was observed to increase by about 100% upon heating for 3.5 min at 100C and 1.5 min at 125C. The signal intensity was found to increase further by about 80% upon a 10 sec exposure to a high-intensity (3.2 kW/cm^2) 785-nm cw laser, corresponding to 40 mW in a 40+/-5-um diameter spot. The observed increase in the SERS signal may be understood by considering the presence of benzenethiol molecules in an intermediate or 'precursor' state in addition to conventionally ordered molecules forming a self-assembled monolayer. The increase in the SERS signal arises from the conversion of the molecules in the precursor state to the chemisorbed state due to thermal and photo-thermal effects.

Filamentation-assisted self-compression of subpetawatt laser pulses to relativistic-intensity subcycle field waveforms

Filamentation-assisted spatiotemporal dynamics of ultrashort laser pulses in the regime of extreme light powers is shown to enable self-compression of subpetawatt laser pulses to relativistic field intensities and subcycle pulse widths. Our supercomputer simulations demonstrate compression of 6-J, 30-fs laser pulses at a central wavelength of 800 nm to 1.3-fs sub-100-TW broadband field waveforms and reveal the generation of relativistic-intensity subfemtosecond field transients as a result of such a pulse evolution scenario, with multiple filamentation avoided due to low gas pressures and the balance between Kerr and ionization nonlinearities steered toward optimal pulse compression due to the depletion of outer-shell ionization in a high-intensity laser field.

Dynamics of Coulomb explosion of Xe clusters in an ultrafast high-intensity laser field

Under the classical particle-dynamics simulation, Coulomb explosion of small Xe clusters in an intense femtosecond laser field and energies of the generated particles are studied. Our results show that the average kinetic energy of the generated ions increases with the cluster size. The dependence of the average kinetic energy of the product ions on the number of atoms inside Xe clusters and the change of average ions charge states from different shells of Xe561 within the interactional time are studied. The oscillation of the mass center of electrons along the direction of the laser electric field is calculated and the time evolutions of the total potential energy and the total kinetic energy of all the product particles are presented here. The total kinetic energy of Xe ions and free electrons are also calculated as functions of the interactional time.

Optical and THz signatures of sub-cycle tunneling dynamics

We present experimental observation of optical signals induced by tunnel ionization and a theoretical model for the generation of new optical and THz frequencies in media ionized by a high intensity laser field. The emergence of sidebands is treated as an integral part of the same underlying process of electron-plasma emission through tunneling. First, investigating the broadly transparent case of gaseous media, we demonstrate the ability to detect multiple new frequency components in the probe field direction, and describe in detail how such tunnel-ionization induced signals can be reliably separated from concomitant nonlinear responses. Second, we apply the same pump–probe method to transparent dielectrics, thus expanding the field of attosecond physics to systems where direct detection of charged particles is unfeasible. Third, we show that a probe beam with a central frequency tuned close to the half of the pump frequency acquires a tunable sideband with a frequency close to zero.

Steady-state correlations of two atoms interacting with a reservoir

We consider two two-level atoms fixed at different positions, driven by a resonant monochromatic laser field, and interacting collectively with the quantum electromagnetic field. A Born-Markov-secular master equation is used to describe the dynamics of the two atoms and the steady-state is obtained analytically for a configuration of the atoms. The steady-state populations of the energy levels of the free atoms, entanglement, quantum and geometric discords and degree of mixedness are calculated analytically as a function of the laser field intensity and the distance between the two atoms. It is found that there is a possibility of considerable steady-state entanglement and left/right quantum discord and that these can be controlled either by increasing/decreasing the intensity of the laser field or by increasing/decreasing the distance between atoms. It is shown that the system of two atoms can be prepared in a separable mixed state with non-zero quantum discord that turns into an $X$-state for high laser field intensities. The behavior and relationships between the different correlations are studied and several limiting cases are investigated.

Sensitivity to dark energy candidates by searching for four-wave mixing of high-intensity lasers in the vacuum

Theoretical challenges to understand Dark Matter and Dark Energy suggest the existence of low-mass and weakly coupling fields in the universe. The quasi-parallel photon-photon collision system (QPS) can provide chances to probe the resonant production of these light dark fields and the induced decay by the coherent nature of laser fields simultaneously. By focusing high-intensity lasers with different colors in the vacuum, new colors emerge as the signature of the interaction. Because four photons in the initial and final states interplay via the dark field exchange, this process is analogous to four-wave mixing in quantum optics, where the frequency sum and difference among the incident three waves generate the fourth wave with a new frequency via the nonlinear property of crystals. The interaction rate of the four-wave mixing process has the cubic dependence on the intensity of each wave. Therefore, if high-intensity laser fields are given, the sensitivity to the weakly coupling of dark fields to photons rapidly increases over the wide mass range below sub-eV. Based on the experimentally measurable photon energies and the linear polarization states, we formulate the relation between the accessible mass-coupling domains and the high-intensity laser parameters, where the effects of the finite spectrum width of pulse lasers are taken into account. The expected sensitivity suggests that we have a potential to explore interactions at the SuperPlanckian coupling strength in the sub-eV mass range, if the cutting-edge laser technologies are properly combined.

Opportunities of Fundamental Physics with High-Intensity Laser Fields

We introduce a research initiative for fundamental physics with a rationale to take advantage of the recent growth of world-wide movements such as ELI and IZEST in constructing high-intensity laser facilities. The three major directions on the fundamental physics research are discussed. §1. Domains of manifestation of physical laws

Probing Dark Energy with High-Intensity Laser Field

Probing Dark Energy with High-Intensity Laser Field

Limitations of high-intensity soft X-ray laser fields for the characterisation of water chemistry: Coulomb explosion of the octamer water cluster

In this work, the Coulomb explosion of the octamer water cluster has been studied employing a theoretical approach. Instead of the usual methodology that makes use of classical molecular dynamics, time-dependent density functional theory has been applied to tackle the problem. This method explicitly accounts for the laser field and thus does not impose any constraint on the interaction between the laser pulse and the cluster. We focus on the effects of energetic changes in the system under high-intensity soft X-ray laser pulses. The motions of the ions and their velocities during this process show significant differences for the three applied laser intensities (10(14), 10(15) and 10(16) W cm(-2)). Very strong soft X-ray free electron laser (FEL) pulses must be short to allow for investigations of ultra-fast wet chemistry, according to the principle of collect and destroy.

Electron-ion dynamics in laser-assisted desorption of hydrogen atoms from H-Si(111) surface

In the framework of real time real space time-dependent density functional theory we have studied the electron-ion dynamics of a hydrogen-terminated silicon surface H-Si(111) subjected to intense laser irradiation. Two surface fragments of different sizes have been used in the simulations. When the intensity and duration of the laser exceed certain levels (which depend on the wavelength) we observe the desorption of the hydrogen atoms, while the underlying silicon layer remains essentially undamaged. Upon further increase of the laser intensity, the chemical bonds between silicon atoms break as well. The results of the simulations suggest that with an appropriate choice of laser parameters it should be possible to remove the hydrogen layer from the H-Si(111) surface in a matter of a few tens of femtoseconds. We have also observed that at high laser field intensities (2–4 V/Å in this work) the desorption occurs even when the laser frequency is smaller than the optical gap of the silicon surface fragments. Therefore, nonlinear phenomena must play an essential role in such desorption processes.

Numerical investigation of atomic dynamics in strong ultrashort laser pulses

The algorithms for the numerical solution of the stationary and nonstationary Schrödinger equations that allow the analysis of the dynamics of single-electron atoms in the presence of an external strong linearly polarized electromagnetic field in the dipole approximation are presented. Several examples of the simulation of atomic dynamics in the presence of high-intensity laser fields are considered to illustrate the possibilities of the proposed algorithms.

Relativistic birefringence induced by a high-intensity laser field in a plasma

Field-induced birefringence, also known as cross-polarization wave generation, has played an important role in ultrafast nonlinear optics. In this paper we analyze birefringence induced by relativistic collective motion of electrons driven by a high-intensity laser field. An analytical expression for the phase difference between the parallel and perpendicular polarizations of a weak probe pulse with respect to the polarization of a strong pump pulse as a function of intensity, density, and wavelengths is derived. It is shown that under typical experimental conditions of high-field physics, the effect is well above detection threshold. The analysis is compared with particle-in-cell simulations, and the agreement provides good support for the theory.