Laser Field Research Articles

Delayed fragmentation of weakly bound Kr2.

We report the experimental observation of the delayed fragmentation of the weakly bound dimer Kr2+ produced through the single ionization of Kr2 by a femtosecond laser field. The observed time delay between ionization and fragmentation, which reflects the survival time of the resulting Kr2+, is measured on the microsecond timescale. A detailed analysis of the kinetic energy releases of the ejected fragments and photoelectrons suggests that this delayed fragmentation arises from the radiative decay of the long-lived Kr2+, transitioning from the bound state II(1/2u) to the repulsive state I(1/2g).

Effects of magnetic, electric, and non-resonant intense laser fields on exciton binding energy and exciton absorption in a symmetric Gaussian single quantum well

Effects of magnetic, electric, and non-resonant intense laser fields on exciton binding energy and exciton absorption in a symmetric Gaussian single quantum well

TiC reinforced Ti6Al4V fabricated by circular oscillating laser directed energy deposition: Microstructure and wear resistance

Gaussian laser is a common laser source in the field of laser directed energy deposition (L-DED). However, Gaussian laser sources have certain limitations, as they produce elevated temperature differentials and internal stresses during L-DED, which can result in significant distortion and fracturing. To address these restrictions, this research proposes using a circular oscillating laser as the energy source for L-DED. TC4 deposition samples and 5 wt% TiC/TC4 composite deposition samples were prepared using both Gaussian laser directed energy deposition (GL-DED) and circular oscillating laser directed energy deposition (COL-DED), and the deposition samples prepared under the two laser modes were compared and studied. The results indicate that, in the process of COL-DED, the laser oscillates periodically at a constant frequency in the high-temperature molten pool, which produces a more consistent temperature gradient and improved stirring effect in the molten pool. This inhibits grain growth and effectively refines the grains. Compared to the TiC/TC4 deposition samples prepared with Gaussian laser, the average grain size of COL TiC/TC4 deposition samples decreased by approximately 54.3 %. Due to the effects of the high-power laser beam, TiC particles partially melted and decomposed into Ti and C. As the laser advanced, the molten pool cooled swiftly, ultimately precipitating uniformly distributed gray-white TiC hard phases. Compared to the TC4 alloy prepared with the Gaussian laser, the TiC/TC4 composite material manufactured with a circular oscillating laser exhibited a 24.5 % increase in microhardness (430.76 HV0.2) and a reduction in wear rate of approximately 42.15 % (to 1.4 × 10−6 g/mm). Circular oscillating laser directed energy deposition can, to a certain extent, improve the hardness and wear resistance of materials compared to Gaussian laser directed energy deposition.

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

Abstract We simulate the time-dependent rovibronic wave function of H2 + 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 results obtained using the standard two-state Born-Oppenheimer approximation and a 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.

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 modelling 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 was 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 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.

A polar diatomic molecule under a high-frequency laser field: classical analytical solution

AbstractDynamics of a polar diatomic molecule (represented as the oscillating rotator model) under external fields is the most fundamental problem and the testbed in molecular physics—analogously to the dynamics of hydrogenic atom (represented as the model of an electron in the Coulomb field) under external fields being the most fundamental problem and the testbed in atomic physics. We present the classical analytical study of the dynamical Stark effect in the oscillating rotator under a high-frequency laser field. We obtain the analytical results by using the method of effective potentials. We demonstrate that under the laser field, the rotation frequency increases, while the oscillation frequency decreases, and the amplitude of the oscillations increases. More significantly, the laser field causes the generation of the second harmonic in the oscillations of this system. This is an important, counterintuitive result in studying this fundamental physical system. We also drew attention to some flaws in the literature on this subject.

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.

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 1x1015 W/cm2. 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 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.

Unconventional magnon blockade in a dissipative photon–magnon coupling system

We investigate unconventional magnon blockade (UMB) in a dissipative photon–magnon coupling cavity, where the coherent and dissipative coupling between photon and magnon can be adjusted by the position of the yttrium iron garnet sphere in the cavity. An approximate analytical solution for the statistical property of magnon is provided, which is in good agreement with the results obtained by numerically solving the Lindblad master equation. Our results indicate that UMB can be achieved in the case of dissipative photon–magnon coupling, but not in the case of coherent photon–magnon coupling. Secondly, by adjusting the amplitude of the external laser field, dynamic control of UMB can be achieved. Finally, by solving the Lindblad master equation containing the occupation number of thermal magnon and photon, the statistical properties of magnons will transition from nonclassical to classical. It is shown that the above phenomena originate from the interference between different quantum paths. Our research may provide theoretical possibilities for quantum manipulation schemes at the single-magnon level and open up a new avenue for designing single-magnon sources in a dissipative photon–magnon coupling system.

Coupled cylindrical quantum well wires in broken symmetry: effects of intense laser field on the harmonic generations

Coupled cylindrical quantum well wires in broken symmetry: effects of intense laser field on the harmonic generations

Parity effects in Rydberg-state excitation in intense laser fields

Parity effects in Rydberg-state excitation in intense laser fields

Laser modulation to plateau region and intensity of high-order harmonic generation in monolayer MoTe2

Abstract Through solving semiconductor Bloch equations, we theoretically investigated the high-order harmonic generation in monolayer MoTe2 under laser modulation. Adjusting the laser parameters, the plateau region and intensity of harmonics can be effectively regulated. Changing laser wavelength can regulate the width of platform region and the cutoff order of harmonic spectrum. Platform region widens with the increase of laser wavelength. Under different laser wavelengths, the number of photons that need to be absorbed for electron transition varies, which affects the inter-band transition of electrons. Laser vector potential also varies with the wavelength, affecting the intra-band motion of electrons. Laser field strength can significantly change the harmonic intensity. As the laser field strength increases, the harmonic intensity increases and may generate new plateau in the high-energy region. The emergence of new platform is due to the transition of electrons between conduction bands. Our work provides a theoretical exploration for generating high quality harmonics and understanding the micro mechanism of high-order harmonic generation.

Near-circularly polarized isolated attosecond pulse generation from a current-carrying state of Ar atom by two-color cross-linearly-polarized laser fields

Abstract We theoretically propose an efficient method to generate near-circularly polarized isolated attosecond (as) pulses (NCP-IAPs) from a current-carrying state of Ar atom driven by two-color cross-linearly-polarized laser fields. We find that the ellipticity of high harmonics can be controlled by adjusting the crossing angle of two linearly polarized lasers and the near-circularly polarized supercontinuum harmonics are obtained when the crossing angle is around 140°. Furthermore, we can produce the NCP-IAPs with the ellipticity up to 0.94 and the shortest one achieves 196 as. This work demonstrates the possibility for generating the NCP-IAPs using a current-carrying state of atoms driven by two-color cross-linearly-polarized laser fields.

Resonant tunneling properties of laser dressed hyperbolic Pöschl-Teller double barrier potential

We examine the resonant tunneling properties of the laser-dressed hyperbolic Pöschl-Teller double quantum barrier structure. We use the non-equilibrium Green's function method to investigate structure parameters and electric field bias on the transmission properties of the system. The transmission probabilities and resonance energy levels are significantly influenced by the well widths and barrier heights. The barrier height increases, resonance energy levels shift toward higher values, and the resonance peak width narrows, leading to sharper and more selective tunneling behavior. Our results show that increasing the electric field bias leads to a decrease in the transmission probability at the first resonance peak, but this effect is not as strong for the subsequent peaks. Moreover, we find that changes in the laser field's parameter and structure parameters allow for fine control over the electronic spectra, allowing for modifications like red or blue shifts based on particular needs. The significance of comprehending the interaction among structural factors, external fields, and transmission qualities in quantum barrier structures is highlighted by our research, providing valuable information for the development and enhancement of electronic and optoelectronic systems with customized functionality. Our findings show the laser field has a considerable impact on resonant tunneling properties, opening the door to new device applications.

Electron Correlation in Two-Electron Atoms: A Bohmian Analysis of High-Order Harmonic Generation in the High-Frequency Domain

Abstract In studying interactions between intense laser fields and atoms or molecules, the role of electron correlation effects on the dynamical response is an important and pressing issue to address. Utilizing Bohmian mechanics (BM), we have theoretically explored the two-electron correlation characteristics while generating high-order harmonics in xenon atoms subjected to intense laser fields. We initially employed Bohmian trajectories to reproduce the dynamics of the electrons and subsequently utilized time-frequency analysis spectra to ascertain the emission time windows for high-order harmonics. Within these time windows, we classified the nuclear region Bohmian trajectories and observed that intense high-order harmonics are solely generated when paired Bohmian particles (BPs) concurrently appear in the nuclear region and reside there for a duration within a re-collision time window. Furthermore, our analysis of characteristic trajectories producing high-order harmonics led us to propose a two-electron re-collision model to elucidate this phenomenon. The study demonstrates that intense high-order harmonics are only generated when both electrons are in the ground state within the re-collision time window. This work discusses the implications of correlation effects between two electrons and offers valuable insights for studying correlation in multi-electron high-order harmonic generation.

Beam instability of broadband stochastic laser fields

Beam instability of broadband stochastic laser fields

Stabilizing and Guiding Rogue Waves in a Cold Atomic Gas

AbstractRogue waves (RWs) are mysterious nonlinear waves and have attracted much attention in recent years. However, they are usually unstable during propagation. Here, a scheme for stabilizing and guiding optical RWs in a cold atomic gas working under the condition of electromagnetically induced transparency is presented. It is shown that an external potential for probe laser field can be created by using an assisting laser field. If the assisting laser field has the form of Gaussian beam, the instability of the RWs can be largely suppressed. It is also shown that the RWs can be stabilized and guided to propagate along curved trajectories if the assisting laser field has the form of Airy beam. The results reported here contribute to the effort for stabilizing and manipulating RWs, which may have potential applications in optical transmission and information processing.

Relativistic Electrons from Vacuum Laser Acceleration Using Tightly Focused Radially Polarized Beams.

We generate a tabletop pulsed relativistic electron beam at 100Hz repetition rate from vacuum laser acceleration by tightly focusing a radially polarized beam into a low-density gas. We demonstrate that strong longitudinal electric fields at the focus can accelerate electrons up to 1.43MeV by using only 98GW of peak laser power. The electron energy is measured as a function of laser intensity and gas species, revealing a strong dependence on the atomic ionization dynamics. These experimental results are supported by numerical simulations of particle dynamics in a tightly focused configuration that take ionization into consideration. For the range of intensities considered, it is demonstrated that atoms with higher atomic numbers like krypton can favorably inject electrons at the peak of the laser field, resulting in higher energies and an efficient acceleration mechanism that reaches a significant fraction (≈14%) of the theoretical energy gain limit.

Laser field effect on binding energy and self-polarization of an impurity in a double square quantum well made of three different materials

Laser field effect on binding energy and self-polarization of an impurity in a double square quantum well made of three different materials

Ripple and Lotus Phenomenon: Radiation Pattern Evolution of Nonlinear Thomson Scattering Under Cooperative and Competitive Effects of Applied Magnetic and Laser Field

Ripple and Lotus Phenomenon: Radiation Pattern Evolution of Nonlinear Thomson Scattering Under Cooperative and Competitive Effects of Applied Magnetic and Laser Field