High-intensity Laser Field Research Articles

Study on the Removal Depth of the Surface Plastic Domain of Silicon-Modified Silicon Carbide

Silicon carbide (Sic) materials find wide-ranging applications in advanced optical systems within the aerospace, astronomical observation, and high-intensity laser fields. The silicon-modified Sic used in this study was created by depositing an amorphous silicon film on the surface of a Sic substrate using electron beam evaporation. Such hard and brittle materials often yield smooth surfaces when subjected to plastic removal. To address the issue of the removal depth of the surface plastic domain for silicon-modified Sic, we propose a method to calculate the indentation depth based on the critical load for the transition from plastic to brittle removal. We conducted a series of nanoindentation and nanoscratching experiments. The critical depth formula was validated through mechanical parameters such as hardness, elastic modulus, and fracture toughness, and the theoretical critical depth of the modified silicon layer was calculated to be 2.71 μm. The research results indicate that the critical load for obtaining the plastic-to-brittle transition point during the nanoindentation experiment is 886 mN, at which point the depth of plastic removal is 2.95 μm, closely matching the theoretical value. The measurements taken with an atomic force microscope near the critical load reveal a scratch depth of 3.12 μm, with a relative error of less than 5% when compared to the calculated value. This study establishes a solid foundation for achieving high-quality surface processing.

Interference patterns in ionization of Kramers–Henneberger atom

We combine IR pump and XUV probe laser pulses to visualize the Kramers–Henneberger (KH) state of the potassium atom. We demonstrate that ionization of such an atom exhibits some molecular-like features such as low order interference maxima in photoelectron momentum spectra. The locations of these maxima allow to estimate spatial dimensions of the KH atom and can be used for accurate calibration of high intensity laser fields. At the same time, we show that an analogy between the KH atom and a homo-nuclear diatomic molecule cannot be extended too far. In particular, higher order interference maxima are very difficult to observe in the case of the KH state. We attribute this to a particular structure of the KH potential which does not confine electron motion to a well-defined potential well unlike in real diatomic molecules.

Numerical calculations of multiphoton molecular absorption

Motivated by the possibility of multiphoton-driven pump-probe experiments, such as time-resolved photoelectron spectroscopy, we carry out essential states's calculations of strong-field molecular excitation by solving the time-dependent Schr\"odinger equation for a molecule in a high-intensity laser field. Usually such calculations rely on adiabatic elimination, but here we make direct use of a large number of energies and transition dipole moments obtained from electronic structure calculations. In this way, we capture a range of multiphoton absorption orders, from 2 to 5, and include dynamic Stark shifts naturally. We consider a range of laser frequencies and intensities to characterize several multiphoton resonances and dynamic Stark shifts. The calculations also include averaging over molecular orientation and geometry, but are carried out for frozen nuclei, which is relevant in the limit of very short laser pulses ($<10$ fs). Here we focus on the molecule thiophene; however, these calculations can easily be implemented for other molecules with appropriate electronic structure input.

Formula omitted]-boson production via the weak process [formula omitted] in the presence of a circularly polarized laser field

In the centre of mass frame, we have studied theoretically the Z-boson resonant production in the presence of an intense laser field via the weak process e+e−→μ+μ−. Dressing the incident particles by a Circularly Polarized laser field (CP-laser field), at the first step, shows that for a given laser field’s parameters, the Z-boson cross section decreases by several orders of magnitude. We have compared the Total Cross Section (TCS) obtained by using the scattering matrix method with that given by the Breit-Wigner approach in the presence of a CP-laser field and the results are found to be very consistent. This result indicates that Breit-Wigner formula is valid not only for the laser-free process but also in the presence of a CP-laser field. The dependence of the laser-assisted differential cross section on the Centre of Mass Energy (CME) for different scattering angles proves that it reaches its maximum for small and high scattering angles. At the next step and by dressing both incident and scattered particles, we have shown that the CP-laser field largely affects the TCS, especially when its strength reaches 109Vcm−1. This result is interpreted by the fact that heavy interacting particles require high laser field intensities to affect the collision’s cross section.

Spatial radiation features of circularly polarized tightly focused laser beams colliding with electrons

In the framework of laser-matter interaction and nonlinear Thomson scattering, we investigate the three-dimensional (3D) motion trajectories and spatial radiation characteristics of the colliding motion electrons with tightly focused circularly polarized Gaussian pulses at different intensities. Combined with the 3D spatial images and the analysis of specific two-dimensional unfolded images, we discover that the amplitude of the motion trajectory increases steadily with increasing laser intensity, the peak radiation power increases rapidly, and the peak radiation azimuth decreases slowly. In addition, by studying the electron motion under the high-intensity () laser field, we find that the electron motion is retrograde twice when interacting with pulsed laser once. Lastly, by extracting the direction and energy of spatial radiation, we indicate that the existence of a specific laser intensity can make the peak radiation azimuth and which intienity provides the maximum conversion rate of laser energy to the peak power of radiation.

Formation of Fractal Dendrites by Laser-Induced Melting of Aluminum Alloys.

We report on the fabrication of fractal dendrites using laser-induced melting of aluminum alloys. We target boron carbide (BC), which is one of the most effective radiation-absorbing materials characterized by a low coefficient of thermal expansion. Due to the high fragility of BC crystals, we were able to introduce its nanoparticles into a stabilization aluminum matrix of AA385.0. The high-intensity laser field action led to the formation of composite dendrite structures under the effect of local surface melting. Modelling the dendrite cluster growth confirms its fractal nature and sheds light on the pattern behavior of the resulting quasicrystal structure.

Role of wavelength in photocarrier absorption and plasma formation threshold under excitation of dielectrics by high-intensity laser field tunable from visible to mid-IR

The development of high power mid-IR laser applications requires a study on laser induced damage threshold (LIDT) in the mid-IR. In this paper we have measured the wavelength dependence of the plasma formation threshold (PFT) that is a LIDT precursor. In order to interpret the observed trends numerically, a model describing the laser induced electron dynamics, based on multiple rate equations, has been developed. We show both theoretically and experimentally that PFT at mid-IR wavelengths is controlled by a transition from weak- to strong-field regime of free carrier absorption. In the case of MgF_2 this transition occurs around 3–4 upmum corresponding to the region of the lowermost PFT. The region of the uppermost PFT is reached around 1 upmum and is governed by an interplay of photoionization and weak-field free carrier absorption which manifests itself in both MgF_2 and SiO_2. The PFT observed in considered materials exhibits a universal dependence on the excitation wavelength in dielectrics. Thus, the presented results pave the route towards efficient and controllable laser-induced material modifications and should be of direct interest to laser researchers and application engineers for prevention of laser-induced damage of optical components in high-intensity mid-IR laser systems.

New estimation of the curvature effect for the X-ray vacuum diffraction induced by an intense laser field

Abstract Quantum electrodynamics predicts X-ray diffractions under a high-intensity laser field via virtual charged particles, and this phenomenon is called vacuum diffraction (VD). In this paper, we derive a new formula to describe VD in a head-on collision geometry of an X-ray free-electron laser (XFEL) pulse and a laser pulse. The wavefront curvature of the XFEL pulse is newly considered in this formula. With this formula, we also discuss the curvature effect on VD signals based on realistic parameters at the SACLA XFEL facility.

Laser polarization dependence of strong-field ionization in lithium niobate

Laser micromachining techniques using femtosecond laser pulses are employed for the fabrication of a wide range of devices, from optical waveguides and fiber Bragg gratings to microfluidic systems. In this perspective, it is important to characterize how transparent materials respond to the high-intensity laser field in order to fully understand and control the strong-field ionization process at the core of such techniques. Here, we characterize the laser polarization dependence of $y$-cut and $x$-cut ferroelectric lithium niobate (${\mathrm{LiNbO}}_{3}$) upon ionization. Using linearly polarized 1800-nm femtosecond pulses, we perform single-shot laser-induced ablation measurements to obtain a macroscopic observable with a large contrast compared to all-optical techniques. In the tunnel ionization regime, the crystal orientation can be correlated with the structural symmetry/asymmetry of the material. This is revealed through a variation of the ablated area when the laser polarization is rotated with respect to the $c$ axis of the crystal. It is further found that ablation is more pronounced when the laser polarization is oriented towards angular regions containing Nb-O bonds of the unit cell, identifying the main chemical bonds contributing to the ionization of the material. The experimental results are supported by numerical simulations based on a two-band model for ${\mathrm{LiNbO}}_{3}$.

Boosting Quantum Vacuum Signatures by Coherent Harmonic Focusing.

We show that coherent harmonic focusing provides an efficient mechanism to boost all-optical signatures of quantum vacuum nonlinearity in the collision of high-intensity laser fields, thereby offering a promising route to their first experimental detection. Assuming two laser pulses of given parameters at our disposal, we demonstrate a substantial increase of the number of signal photons measurable in experiments where one of the pulses undergoes coherent harmonic focusing before it collides with the fundamental-frequency pulse. Imposing a quantitative criterion to discern the signal photons from the background of the driving laser photons and accounting for the finite purity of polarization filtering, we find that signal photons arising from inelastic scattering processes constitute a promising signature. By contrast, quasielastic contributions which are conventionally assumed to form the most prospective signal remain background dominated. Our findings may result in a paradigm shift concerning which photonic signatures of quantum vacuum nonlinearity are accessible in experiment.

Terahertz Generation Enhanced by Nonlinear Filaments Interaction in Liquids

Enhanced terahertz (THz) radiation was observed in liquids via interaction of two noncollinear filaments of ultrashort pulses. As compared with THz generation driven by one filament, the observed enhancement was attributed to asymmetric plasma current due to filament-induced multiple frequency components in liquids. By tuning the relative polarization angles and pulse energies of the interacting filaments, we demonstrated that the interaction of the two filaments gave rise to plasma density modulation and high-intensity laser field in the intersection region, which resulted in blue-shifted supercontinuum generation. The newly generated blue frequency components enhanced asymmetric plasma current when it combined with the fundamental-wave filament at 800 nm, which led to stronger THz generation.

Non-perturbative multiphoton excitation studies in an excitonic coupled quantum well system using high-intensity THz laser fields

Multiphoton excitations and nonlinear optical properties of exciton states in GaAs/AlxGa1−xAs coupled quantum well structure have been theoretically investigated under the influence of a time-varying high-intensity terahertz (THz) laser field. Non-perturbative Floquet theory is employed to solve the time-dependent equation of motion for the laser-driven excitonic quantum well system. The response to the field parameters, such as intensity and frequency of the laser electric field on the state populations, can be used in various optical semiconductor device applications, such as photodetectors, sensors, all-optical switches, and terahertz emitters.

A Frenet–Serret interpretation of particle dynamics in high-intensity laser fields

In this paper we discuss the dynamics of charged particles in high-intensity laser fields in the context of the Frenet–Serret formalism, which describes the intrinsic geometry of particle world lines. We find approximate relations for the Frenet–Serret scalars and basis vectors relevant for high-intensity laser particle interactions. The onset of quantum effects relates to the curvature radius of classical trajectories being on the order of the Compton wavelength. The effects of classical radiation reaction are discussed, as well as the classical precession of the spin-polarization vector according to the Thomas–Bargman–Michel–Telegdi equation. We comment on the derivation of the photon emission rate in strong-field QED beyond the locally constant field approximation, which is used in Monte Carlo simulations of quantum radiation reaction. Such a numerical simulation is presented for a possible experiment to distinguish between classical and quantum mechanical models of radiation reaction.

Stochastic mechanics for ponderomotive effect of a spin-less electron interacting with a high-intensity plane wave laser field

We discuss the relativistically covariant ponderomotive effect of a spin-less electron by a high-intensity laser field of a plane wave in the quantum regime. At first we recall the relativistic ponderomotive effect in classical mechanics. Then against that, we will investigate quantum mechanical expression of the ponderomotive effect by relativistic stochastic mechanics, where, we also propose relativistic stochastic mechanics to draw a trajectory of a spin-less electron. After giving a strict solution of stochastic mechanics, its slowly varying motion is examined as its ponderomotive effect in the quantum regime. Finally, we will see the universality of the ponderomotive effect acting on a spin-less electron interacting with a present high-intensity femtosecond laser, via the dressed (effective) mass of a spin-less electron bridging between classical and quantum mechanics.

Measuring the boiling point of the vacuum of quantum electrodynamics

It is a long-standing non-trivial prediction of quantum electrodynamics that its vacuum is unstable in the background of a static, spatially uniform electric field and, in principle, sparks with spontaneous emission of electron-positron pairs. However, an experimental verification of this prediction seems out of reach because a sizeable rate for spontaneous pair production requires an extraordinarily strong electric field strength $|\mathbf E|$ of order the Schwinger critical field, ${\rm E}_c=m_e^2/e\simeq 1.3\times 10^{18}\ {\rm V/m}$, where $m_e$ is the electron mass and $e$ is its charge. Here, we show that the measurement of the rate of pair production due to the decays of high-energy bremsstrahlung photons in a high-intensity laser field allows for the experimental determination of the Schwinger critical field and thus the boiling point of the vacuum of quantum electrodynamics.

Simulation of laser induced absorption phenomena in transparent materials

The laser-induced damage in transparent optical materials represents an important active field of research as part of laser/material interactions studies. Most of research activities within this field are aiming to laser micro-processing of transparent optical materials, glasses and ceramics. An example of such laser micro-processing techniques is drilling micro channels through a glass plate and drilling transverse holes through single mode optical fibre cladding and core. The latter example of research activity has an important purpose consisting of designing and manufacturing micro-nanoscale optical fibre sensors with improved capabilities. Regarding these applicative research activities, there are two important correlated issues here to be underlined. The first one consists in the fact that high intensity laser field induced electron density variation into a transparent material is the main mechanism of breakdown and damage, that is, basis of micro-processing. The second one refers to the necessity of developing simulation procedures based on accurate theoretical models of these physical processes in order to use an accurate computer control of micro-processing technology. The main purpose of this work is to present the results of simulations in electron density variation induced by high intensity laser pulses in various transparent materials.

Femtosecond laser pulse modification of amorphous silicon films: control of surface anisotropy

A one-dimensional surface relief with a 1.20 ± 0.02 µm period was formed in amorphous hydrogenated silicon films as a result of irradiation by femtosecond laser pulses (1.25 µm) with a fluence of 0.15 J cm−2. Orientation of the formed structures was determined by the polarization vector of the radiation and the number of acting pulses. Nanocrystalline silicon phases with volume fractions from 40 to 67% were detected in the irradiated films according to the analysis of Raman spectra. Observed micro- and nanostructuring processes were caused by surface plasmon–polariton excitation and near-surface region nanocrystallization, respectively, in the high-intensity femtosecond laser field. Furthermore, the formation of Si-III and Si-XII silicon polymorphous modifications was observed after laser treatment with a large exposure dose. The conductivity of the film increased by three orders of magnitude at proper conditions after femtosecond laser nanocrystallization compared to the conductivity of the untreated amorphous surface. The conductivity anisotropy of the irradiated regions was also observed due to the depolarizing contribution of the surface structure, and the non-uniform intensity distribution in the cross-section of the laser beam used for modification.

Probing vacuum birefringence under a high-intensity laser field with gamma-ray polarimetry at the GeV scale

Probing vacuum structures deformed by high intense fields is of great interest in general. In the context of quantum electrodynamics (QED), the vacuum exposed by a linearly polarized high-intensity laser field is expected to show birefringence. We consider the combination of a 10 PW laser system to pump the vacuum and 1 GeV photons to probe the birefringent effect. The vacuum birefringence can be measured via the polarization flip of the probe $\gamma$-rays which can also be interpreted as phase retardation of probe photons. We provide theoretically how to extract phase retardation of GeV probe photons via pair-wise topology of the Bethe-Heitler process in a polarimeter and then evaluate the measurability of the vacuum birefringence via phase retardation given a concrete polarimeter design with a realistic set of laser parameters and achievable pulse statistics.

Prospects of odd and even harmonic generation by an atom in a high-intensity laser field

A new approach for studying the spontaneous emission of an atomic system in the presence of a high-intensity laser field is used to study the process of harmonic generation. The analysis is based on consideration of quantum system interaction, with the quantized field modes being in the vacuum state, while the intense laser field is considered to be classically beyond perturbation theory. The numerical analysis of the emission from the single one-electron 1D atom irradiated by the femtosecond laser pulse of a Ti:Sa laser is discussed. It is demonstrated that not only odd, but also even harmonics can be emitted if the laser field is strong enough. The origin of the appearance of even harmonics is studied. The obtained results are compared with those found in the framework of the semiclassical approach that is widely used to study harmonic generation. It is found that the semiclassical approach is inapplicable in the strong-field limit.

Thermal effects in systems of colloidal plasmonic nanoparticles in high-intensity pulsed laser fields [Invited]: publisher’s note

Thermal effects in systems of colloidal plasmonic nanoparticles in high-intensity pulsed laser fields [Invited] : publisher's note (vol 7,pg 555, 2017)