Laser Field Research Articles

VACUUM BIREFRINGENCE AND DICHROISM IN A STRONG PLANE-WAVE BACKGROUND

In the present study, we consider the effects of vacuum birefringence and dichroism in strong electromagnetic fields. According to quantum electrodynamics, the vacuum state exhibits different refractive properties depending on the probe photon polarization and one also obtains different probabilities of the photon decay via production of electron-positron pairs. Here we investigate these two phenomena by means of several different approaches to computing the polarization operator. The external field is assumed to be a linearly polarized plane electromagnetic wave of arbitrary amplitude and frequency. Varying the probe-photon energy and the field parameters, we thoroughly examine the validity of the locally-constant field approximation (LCFA) and techniques involving perturbative expansions in terms of the external-field amplitude. Within the latter approach, we develop a numerical method based on a direct evaluation of the weak-field Feynman diagrams, which can be employed for investigating more complex external backgrounds. The polarization operator depends on two parameters: classical nonlinearity parameter ξ and the product η = ωq0/m2 of the laser field frequency ω and the photon energy q0 (m is the electron mass). The domains of validity of the approximate techniques in the ξη plane are explicitly identified.

Saddle point analysis on selective enhancement of high-order harmonic generation

We theoretically demonstrate control of selective enhancement of the near-cutoff odd order harmonic generation by dual-color chirped laser field. The sharp enhancements of a single harmonic order ranging from H37 to H59 (λ h =21.6nm-13.5nm) are achieved by adjusting the intensity of the fundamental frequency field. The saddle point method is applied to the analysis of high-order harmonic generation using the distorted-waveform laser field. A series of orbits of principal contribution to enhancement are extracted using the saddle point method, and the enhancement of the key orbits’ interference is reconstructed by quantum orbital theory. Through the analysis of the interference mechanism of enhancement, we give a full explanation of the dependence of enhanced harmonic order on laser intensity.

Parity effects in Rydberg-state excitation in intense laser fields

Conservation of parity plays a fundamental role in our understanding of various quantum processes. However, it is difficult to observe in atomic and molecular processes induced by a strong laser field due to their multiphoton character and the large number of states involved. Here we report an effect of parity in strong-field Rydberg-state excitation (RSE) by comparing the RSE probabilities of the N2 molecule and its companion atom Ar, which has a similar ionization potential but opposite parity of its ground state. Experimentally, we observe an oscillatory structure as a function of intensity with a period of about 50 TW/cm2 in the ratio between the RSE yields of the two species, which can be reproduced by simulations using the time-dependent Schrödinger equation (TDSE). We analyze a quantum-mechanical model, which allows for interference of electrons captured in different spatial regions of the Rydberg-state wave function. In the intensity-dependent RSE yield, it results in peaks with alternating heights with a spacing of 25 TW/cm2 and at the same intensity for both species. However, due to the opposite parities of their ground states, pronounced RSE peaks in Ar correspond to less pronounced peaks in N2 and vice versa, which leads to the period of 50 TW/cm2 in their ratio. Our work reveals a novel parity-related interference effect in the coherent-capture picture of the RSE process in intense laser fields.

Effect of external magnetic field inhomogeneity on the nonlinear absorption of intense laser pulse in inhomogeneous warm plasma

This paper studies the propagation of an intense laser pulse and the collisional absorption in an inhomogeneous warm plasma by taking into account the external magnetic field inhomogeneity and the ponderomotive force. The calculations are carried out and compared for different magnetic field strengths and their various configurations. For this purpose, using the hydrodynamic equations, the electron density and hence the effective dielectric permittivity of the magneto-active warm plasma are derived and the nonlinear wave equation is solved through the numerical method of Runge–Kutta. The results show that increasing the strength of the external magnetic field causes an increase in the absorption coefficient and the linear magnetic field has a higher influence on the absorption coefficient with respect to the wiggler and constant magnetic fields. Moreover, when the electron temperature increases, the amplitude of the laser field and the absorption coefficient are increased and the spatial damping rate of the laser pulse takes a peak in the plasma. The results also indicate that increasing the energy of the laser pulse causes a decrease in the nonlinear absorption, and the laser energy spatial damping is significantly decreased in contrast to the growth of the amplitude of the laser field. A qualitative comparison of the results indicates that if a linear magnetic field is applied in the same direction of the laser propagation, the collisional absorption rate will be larger with respect to the other magnetic fields. Moreover, the difference in the influence of the mentioned magnetic fields on the collisional absorption increases with increasing the electron temperature and normalized cyclotron frequency and decreases with increasing laser intensity.

Interband and intraband transitions, as well as charge mobility in driven two-band model with electron-phonon coupling.

Interband and intraband transitions are fundamental concepts in the study of electronic properties of materials, particularly semiconductors and nanomaterials. These transitions involve the movement of electrons between distinct energy states or bands within a material. In addition, charge mobility is also a critical parameter in materials science and electronics. A thorough understanding of these transitions and mobility is critical for the development and optimization of advanced electronic and optoelectronic devices. In this study, we investigate the influence of external periodic drivings on interband and intraband transitions, as well as charge mobility, within a driven two-band model that includes electron-phonon coupling. These external periodic drivings can include a periodic laser field, a time-varying magnetic or electric field, or an alternating current voltage source. We have developed the Floquet surface hopping and Floquet mean field methods to simulate electronic dynamics under various drivings in both real and reciprocal spaces. Our findings demonstrate that periodic drivings can enhance interband transitions while suppressing intraband transitions. In addition, charge mobility is restrained by these external periodic drivings in the driven two-band model.

A Review on Corrosion Behavior and Surface Modification Technology of Nickel Aluminum Bronze Alloys: Current Research and Prospects

Nickel aluminum bronze alloy, a complex alloy containing multiple phases, has become the most common material for naval propellers due to its good corrosion resistance. Traditional cast nickel aluminum bronze shows serious corrosion behavior in harsh service environments. This article reviews progress on the corrosion behaviors and corrosion mechanism of nickel aluminum bronze in highly corrosive and complex marine environments and systematically discusses the research status of the surface modification technologies such as laser surface strengthening, mechanical shot peening, friction stir and thermal spraying, and so on. To improve the comprehensive performance of nickel aluminum bronze, this work focuses on analyzing the effect of process parameters on the corrosion resistance of nickel aluminum bronze alloy while researching propeller blade surface modification technology. Finally, the future research and development direction of nickel aluminum bronze in the fields of laser and arc additive manufacturing is prospected.

Advanced electron acceleration via chirped Hermite–Cosh–Gaussian laser and magnetic field interaction

Advanced electron acceleration via chirped Hermite–Cosh–Gaussian laser and magnetic field interaction

Strong-field nondipole approximation in laser-assisted thermal electron scattering

This study investigates the differential cross-section (DCS) of electrons scattered by a hydrogen molecule (H₂) under varying conditions, including temperature, momentum, laser intensity, and polarization. The objective was to understand how these parameters affect electron scattering and to compare the effects of linear and circular polarizations. Methodologically, theoretical model was developed using strong-field nondipole approximation with linear and circular polarized laser fields, examining DCS as a function of thermal electron temperature, momentum, and laser intensity. The study utilized a modified Volkov wave function model to account for thermal electron effects and analyzed DCS variations across different orbitals (n = 1, n = 2, and n = 3). Findings reveal that DCS increases with temperature due to enhanced electron oscillations, with higher orbitals (n = 3) showing greater DCS compared to lower orbitals (n = 1). Increased momentum results in decreased DCS, with higher orbitals exhibiting higher DCS values under circular polarization, contrary to linear polarization. Laser intensity decreases DCS for both polarizations, with circular polarization providing a narrower range of DCS values and generally higher DCS compared to linear polarization. This research further exploration of polarization effects on DCS in different atomic systems and extending studies to higher energy regions for a comprehensive understanding of electron scattering dynamics.

Laser-Assisted Scattering With Screened Diatomic Potential

This study explores the differential cross section (DCS) for laser-assisted scattering of diatomic molecules, considering various polarization conditions (linear, circular, elliptical) and potential parameters. The primary objective is to understand how polarization, screening effects, and potential parameters influence the scattering behavior. Utilizing a model that incorporates the Morse potential with screening effects, the analysis treats the laser field classically as a time-dependent, spatially homogeneous electric field, while the electron dynamics are described quantum mechanically using the Schrödinger equation. The Volkov wavefunction is derived, and the first-Born S-matrix element is computed to evaluate the scattering process. The results show that the DCS decreases with increasing screening parameters, with linear polarization yielding higher values than circular or elliptical polarization. Specifically, at an initial momentum of 8 MeV and a final momentum of 9 MeV, the DCS for elliptical polarization is notably higher. The DCS also varies with potential strength and well width, showing a peak at 0.14 Å for potential well width. The findings suggest that linear polarization is most effective for scattering studies under varying potential strengths. It is recommended to focus on linear polarization for enhanced scattering efficiency and to carefully adjust screening parameters and potential well widths for optimal results.

Temperature Dependence of Coherent versus Spontaneous Raman Scattering.

Because of their sub picosecond temporal resolution, coherent Raman spectroscopies have been proposed as a viable extension of spontaneous Raman thermometry, to determine dynamics of mode specific vibrational energy content during out of equilibrium molecular processes. Here we show that the presence of multiple laser fields stimulating the vibrational coherences introduces additional quantum pathways, resulting in destructive interference. This ultimately reduces the thermal sensitivity of single spectral lines, nullifying it for harmonic vibrations and temperature independent polarizability. We demonstrate how harnessing anharmonic signatures such as vibrational hot bands enables coherent Raman thermometry.

Ponderomotive potential effects on strong field two-photon double ionization in neon

Abstract In the context of the recently reported experiment on photoionization in neon atom, we theoretically study the photoionization of neon atom at a comparatively intense laser field. The calculated photoelectron spectrum for a Gaussian laser pulse show an asymmetric double peak line shape at a pulse duration of 14.2 fs and peak intensity of 1 × 1015 W cm−2. A systematic study clearly indicates that the ponderomotive potential of the photoelectron released during photoionization of neon is instrumental in causing the visible asymmetry. Interestingly, for similar laser parameters asymmetry in the photoelectron spectrum gets significantly reduced for a Sech2 shaped laser pulse. Time resolved photoelectron spectrum reveals that even for a Sech2 shaped laser pulse the two peak photoelectron spectrum is initially asymmetric and evolves into a symmetric line shape with increase in time. The results clearly indicate that irrespective of laser pulse shape asymmetry shows a non-linear decrease as a function of time. Our study also shows the possibility of controlling the asymmetry by varying the pulse duration. The calculations establishes a correlation between the effects of direct double ionization and ponderomotive potential on the asymmetry of the photoelectron spectrum at different pulse durations.

Ion motion in strongly magnetized cluster laser plasma

Abstract This paper investigates the interaction of high intensity, circularly polarized, short laser pulses with heavy cluster plasma through analytical modeling and numerical simulations. The optimal parameters were found for the generation of several GigaGs quasi-stationary magnetic field by using the upgraded analytical model and detailed 3D PIC simulations. It is confirmed that a field of such strength slows down the thermal expansion of the cluster core in the direction transverse to the laser beam axis, which can be used in nuclear physics. The generated inward shocks produce ion core compression, which is relevant to nuclear fusion. The electrostatic interaction between the rotating laser field, electrons and ions leads to an ion spiral density distribution in the cluster’s transversal plane, which is absent in a cluster irradiated by linearly polarized pulses with the same parameters.

Evidence of the Quantum Optical Nature of High-Harmonic Generation

High-harmonic generation is a light up-conversion process occurring in a strong laser field, leading to coherent bursts of extreme ultrashort broadband radiation [Lewenstein , Phys. Rev. A , 2117 (1994)]. As a new perspective, we propose that ultrafast strong-field electronic or photonic processes such as high-harmonic generation can potentially generate nonclassical states of light well before the decoherence of the system occurs [Gorlach , Nat. Commun. , 4598 (2020); Stammer ., Phys. Rev. Lett. , 123603 (2022)]. This could address fundamental challenges in quantum technology such as scalability, decoherence, or the generation of massively entangled states [Lewenstein , Luca Argenti Michael Chini, 27 (2024)]. Here, we report experimental evidence of the nonclassical nature of the harmonic emission in several semiconductors excited by a femtosecond infrared laser. By investigating single- and double-beam intensity cross-correlation [Loudon, Rep. Prog. Phys. , 913 (1980)], we measure characteristic nonclassical features in the single-photon statistics. We observe two-mode squeezing in the generated harmonic radiation, which depends on the laser intensity that governs the transition from super-Poissonian to Poissonian photon statistics. The measured violation of the Cauchy-Schwarz inequality realizes a direct test of multipartite entanglement in high-harmonic generation [Wasak, Phys. Rev. A , 033616 (2014)]. This result is supported by the theory of multimodal detection and the Hamiltonian from which the effective squeezing modes of the harmonics can be derived [Gonoskov , Phys. Rev. B , 125110 (2024); Christ New J. Phys. , 033027 (2011)]. With this work, we show experimentally that high-harmonic generation is a new quantum bosonic platform that intrinsically produces nonclassical states of light with unique features such as multipartite broadband entanglement or multimode squeezing. The source operates at room temperature, using standard semiconductors and a standard commercial fiber laser, opening up new routes for the quantum industry, such as optical quantum computing, communication, and imaging. Published by the American Physical Society 2024

Time-dependent rovibronic wave function of H2+ by multiconfiguration theory

Abstract We simulate the time-dependent rovibronic wave function of H 2 + in an intense, few-cycle 400 nm laser field using a time-dependent multiconfiguration method. By calculating the expectation value of the total angular momentum squared, the time-dependent expectation value of the internuclear distance, the induced dipole moment, and the probability of electron ejection, we show that rotational, vibrational and electronic excitation as well as ionization can be simulated. We compare the results obtained using the time-dependent multiconfiguration method with the results obtained using the standard two-state Born-Oppenheimer approximation and the close-coupling expansion. We find that the multiconfiguration results for a wave function constructed using 21 time-dependent orbitals are in good agreement with the close-coupling results, but that the two-state Born-Oppenheimer approximation leads to an underestimation of the induced dipole moment by a factor of two and an overestimation the expectation value of the total angular momentum squared by a factor of 2.3.

Generation of six-lobe photoelectron angular distribution via three-leaf clover laser field

Generation of six-lobe photoelectron angular distribution via three-leaf clover laser field

Photoelectron momentum distribution in structured strong fields

Abstract In this study, a reaction microscope is used to explore the behavior of electrons in shaped beams under strong field conditions. Photoelectron momentum spectra indicate that the inclusion of orbital angular momentum (OAM) of light does not significantly impact the available electron angular momentum states. However, the distinctive donut shape of the beam plays a crucial role in determining the observed Photoelectron Angular Distributions (PADs). TDSE simulations, incorporating focal volume averaging indicates that the geometric properties of the focal region of the OAM and the Gaussian beams affect the photoelectron spectra differently. By averaging the spectra across different intensity regions, we have provided a qualitative explanation for the variations in photoelectron spectra resulting from the shapes of the individual beams. This result shows that the transfer of OAM in ultrashort light pulses cannot be detected in gas ensembles due to the ionization being overwhelmed by atoms in the most intense region with minimal spatial phase variation within the laser field. We demonstrate that the differences in the momentum spectra arising from shaped beams can be qualitatively explained using models that incorporate the spatial averaging of the beam, rather than focusing on the OAM content.

Attosecond transient interferometry

AbstractAttosecond transient absorption resolves the instantaneous response of a quantum system as it interacts with a laser field, by mapping its sub-cycle dynamics onto the absorption spectrum of attosecond pulses. However, the quantum dynamics are imprinted in the amplitude, phase and polarization state of the attosecond pulses. Here we introduce attosecond transient interferometry and measure the transient phase, as we follow its evolution within the optical cycle. We demonstrate how such phase information enables us to decouple the multiple quantum paths induced in a light-driven system, isolating their coherent contribution and retrieving their temporal evolution. Applying attosecond transient interferometry reveals the Stark shift dynamics in helium and retrieves long-term electronic coherences in neon. Finally, we present a vectorial generalization of our scheme, theoretically demonstrating the ability to isolate the underlying anomalous current in light-driven topological materials. Our scheme provides a direct insight into the interplay of light-induced dynamics and topology. Attosecond transient interferometry holds the potential to considerably extend the scope of attosecond metrology, revealing the underlying coherences in light-driven complex systems.

Enhanced laser-target energy coupling through counter-propagating lasers: Insights from electron recirculation

In the interaction between lasers of relativistic intensity and targets, a portion of the laser energy is carried by relativistic fast electrons, which usually cannot be deposited inside but escapes from the target. Here, we explored a method to reduce this energy waste and enhance laser-target energy coupling through counter-propagating lasers. Particle-in-cell simulation results show that high-energy fast electrons generated by the laser on one side can be re-accelerated by the laser on the other side through the synergistic effect of the reflected laser and longitudinal electric field after passing through the target, and then reflected back into the target by a potential barrier, forming an electron recirculation. Through this electron recirculation, the energy conversion efficiency of each laser is significantly improved, and the temperature of electrons and ions inside the target is effectively increased by 118 % and 29 %, respectively. We also explored the effects of laser intensity and target density through multiple sets of simulations with controlled variables, and summarized the electron recirculation model in such counter-propagating lasers configuration.

Effect of orbital symmetry on atomic ionization in near-infrared laser fields

Effect of orbital symmetry on atomic ionization in near-infrared laser fields

Growth, spectroscopy properties, and laser operation of single crystal fiber: Nd3+-doped CNGG

Nd3+-doped calcium niobium gallium garnet single crystal fibers (Nd:CNGG SCFs) with varying Nd3+ concentrations were successfully grown using the laser-heated pedestal growth (LHPG) method. The study thoroughly examines the fundamental physical structure, optical properties, and laser characteristics of the as-grown Nd:CNGG SCFs. Results indicate that the Nd:CNGG SCF exhibits broader absorption and emission full width at half maximum (FWHM) compared to bulk single crystals. Moreover, pumped by a commercial 808 nm laser diode, continuous-wave laser operation at 1061 nm with a half-height width of 1.86 nm was achieved. The laser output power reached 1.04 W at an absorbed power of 7.46 W, with a slope efficiency of 25.4% relative to the absorbed pump power. These findings suggest that Nd:CNGG SCF holds promise as a practical and potent candidate for laser gain medium, offering significant research potential in the field of lasers.