Interaction Of Laser Pulses Research Articles

Selective Ablation and Laser-Induced Periodical Surface Structures (LIPSS) Produced on (Ni/Ti) Nano Layer Thin Film with Ultra-Short Laser Pulses

The interaction of ultra-short laser pulses (USLP) with Nickel/Titanium (Ni/Ti) thin film has been presented. The nano layer thin film (NLTF), composed of ten alternating Ni and Ti layers, was deposited on silicon (Si) substrate by ion-sputtering. A single and multi-pulse irradiation was performed in air with focused and linearly polarized laser pulses. For achieving selective ablation of one or more surface layers, without reaching the Si substrate, single pulse energy was gradually increased from near the ablation threshold value to an energy value that caused the complete removal of the NLTF. In addition to single-pulse selective ablation, the multi-pulse USLP irradiation and production of laser-induced periodic surface structures (LIPSSs) were also studied. In the presented experiment, we found the optimal combination of accumulated pulse number and pulse energy to achieve the LIPSS formation on the thin film. The laser-induced morphology was examined with optical microscopy, scanning electron microscopy, and optical profilometry. To interpret the experimental observations, a theoretical simulation has been performed to explore the thermal response of the NLTFs after irradiation with single laser pulses.

Ultra-Short Pulses Laser Heating of Dielectrics: A Semi-Classical Analytical Model.

Femtosecond laser pulses are currently regarded as an emerging and promising tool for processing wide bandgap dielectric materials across a variety of high-end applications, although the associated physical phenomena are not yet fully understood. To address these challenges, we propose an original, fully analytical model combined with Two Temperatures Model (TTM) formalism. The model is applied to describe the interaction of fs laser pulses with a typical dielectric target (e.g., Sapphire). It describes the heating of dielectrics, such as Sapphire, under irradiation by fs laser pulses in the range of (1012-1014) W/cm2. The proposed formalism was implemented to calculate the free electron density, while numerical simulations of temperature field evolution within the dielectrics were conducted using the TTM. Mathematical models have rarely been used to solve the TTM in the context of laser-dielectric interactions. Unlike the TTM applied to metals, which requires solving two heat equations, for dielectrics the free electron density must first be determined. We propose an analytical model to solve the TTM equations using this parameter. A new simulation model was developed, combining the equations for non-equilibrium electron density determination with the TTM equations. Our analyses revealed the non-linear nature of the physical phenomena involved and the inapplicability of the Beer-Lambert law for fs laser pulse interactions with dielectric targets at incident laser fluences ranging from 6 to 20 J/cm2.

Influence of irradiation wavelength during laser-assisted doping of 4H-silicon carbide in liquid phase

Laser-assisted doping of silicon carbide (SiC) substrates is challenging due to the low diffusion coefficient of dopant atoms and the chemically inert nature of SiC. Single crystal intrinsic 4H-SiC substrate is irradiated with neodymium-doped yttrium aluminium garnet (Nd3+):YAG laser with wavelengths of 1064, 355 and 266 nm, and krypton fluoride (KrF) excimer laser with the wavelength of 248 nm under liquid phase dopant sources. Different liquid solutions were used as dopant sources for aluminium (Al) and phosphorus (P). SiC was transparent to 1064 and 355 nm due to low absorption coefficients, while 266 and 248 nm showed better coupling due to higher absorption coefficients and led to the diffusion of atoms. The electrical resistance of the substrates was measured to be lower than 1000 kΩ after diffusion. Dispersive X-ray spectroscopy (EDS) studies showed that both laser wavelengths of 248 nm and 266 nm resulted in doping of Al and P, with the surface concentrations ranging from 0.5 to 1.5 at.% and from 0.24 to 0.6 at.%, respectively. Two-dimensional thermo-temporal simulation of the laser pulse interaction in the liquid phase revealed that unlike in air, during irradiation with 266 nm laser under liquid, the surface temperature of the substrate was slightly lower. However, the subsurface temperature increased along the depth by a few microns. Similarly, simulation studies with longer pulse irradiation also show that high temperature was maintained for a longer time, indicating improved dopant diffusion into the 4H-SiC substrate.

Acceleration of Electrons upon Interaction of Laser Pulses with Solid Targets in the Laser Peeler Regime

Acceleration of Electrons upon Interaction of Laser Pulses with Solid Targets in the Laser Peeler Regime

Plasma opacity induced by laser-driven movement of background ions

Abstract The transition threshold from relativistically transparent regime to opaque regime in the interaction of an ultra-intense laser pulse and a bulk plasma with mobile background ions is investigated. The threshold corresponds to the onset of laser hole-boring. We show that for an ultra-intense laser, the threshold depends on the ion composition of the plasma, and the corresponding plasma density is significantly lower than that with ion immobile plasma. These are supported by 1D PIC simulations by using hydrogen plasma and fully ionized carbon plasma. The movement of background ions modifies the dynamics and distribution of electrons in the plasma, which results in the Doppler-red-shift of the incident laser and the increase of the effective plasma density. An intuitive model, which gives the dependence of the transparency-opaqueness threshold on laser intensity and frequency, as well as the ion composition, is established. It is tested by multi-dimensional PIC simulations with hydrogen plasma.

A Theoretical Approach to the Investigation of Electrostatic Plasma Waves in Laser Pulse Interaction with Hypothetical Nonuniform Quantum Electron–Positron Magnetoplasma

A Theoretical Approach to the Investigation of Electrostatic Plasma Waves in Laser Pulse Interaction with Hypothetical Nonuniform Quantum Electron–Positron Magnetoplasma

Role of field ionization in laser pulse evolution during interaction of long laser pulse with gaseous hydrogen atoms

Role of field ionization in laser pulse evolution during interaction of long laser pulse with gaseous hydrogen atoms

High repetition-rate 0.5 Hz broadband neutron source driven by the Advanced Laser Light Source

Neutron beams are an essential tool to investigate material structure and perform nondestructive analysis, as they give unique access to element composition, thus ideally complementing density analysis allowed by standard x-rays investigation. Laser-driven neutron sources, though compact and cost-effective, currently have lower average flux than conventional neutron sources, due to the limited repetition rate of the lasers used so far. However, advancements in laser technology allow nowadays to address this challenge. Here, we report results obtained at the Advanced Laser Light Source characterizing stable production of broadband (0.1–2 MeV) neutrons produced at a high repetition rate (0.5 Hz). The interaction of laser pulses of 22 fs duration and 3.2 J on-target energy with 2-μm-thick tantalum targets produced protons in the Target Normal Sheath Acceleration (TNSA) regime up to 7.3 MeV. These protons were subsequently converted into neutrons by (p,n) reactions in lithium fluoride (LiF). Activation measurements and bubble detectors were used to characterize neutron emissions, with a neutron fluence of up to ∼1.4×105 neutrons/shot/sr and energies mainly between a few hundred of kilo-electron volt and 2 MeV. The total neutron yield was ∼5×105 neutrons/shot. This paves the way for numerous applications, e.g., in homeland security, materials science, or cultural heritage.

Pressure scaling of femtosecond laser filamentation in air: Prospects for long-range atmospheric propagation

The principal trend of the last decades is the use of laser systems generating ultrashort (femtosecond) laser pulses of gigawatt and terawatt power in various spheres of human activity, in particular, in atmospheric researches. One of the important challenges within this problem is the use of the unique nonlinear optical phenomena manifesting in the atmosphere as pulse self-focusing, light-induced ionization of the medium, plasma generation and laser filamentation for remote laser diagnostics of the aerosol-gas constituents and efficient delivery of concentrated optical energy over long distances in the atmosphere. This brings to the forefront the problem of increasing the actual length of the nonlinear interaction of an ultrashort laser pulse with medium to kilometer distances whereas real physical length of most existing optical paths is usually limited by several hundred meters. We propose and theoretically substantiate an effective way to solve the problem of long-range atmospheric filamentation by transforming the propagation medium itself using short laboratory traces and optical cuvettes with gases of increased (over-atmospheric) pressure. Following the scaling laws of the optical characteristics of pressurized medium, the coefficients describing the interaction between optical wave and medium increase along with the increase in gas pressure. By the numerical simulations in the framework of the nonlinear Schrodinger equation, we show that this makes it possible to emulate kilometers-long atmospheric traces for laser beams of centimeter diameter and terawatt pulse power on the laboratory scale (tens of meters).

Bound exciton engineering approach for tuning the thermal lensing phenomenon in anatase TiO2: Gd nanosystems

We report a comprehensive investigation of the third-order nonlinear interaction of femtosecond laser pulses with nanostructured anatase TiO2 doped with varying concentrations of gadolinium impurities. The samples were synthesized using a facile sol‒gel method. The physicochemical characteristics of the prepared samples were investigated using various analytical techniques, including XRD, SEM, TEM, SAED, UV‒Vis, PL and XPS. The average crystallite sizes of the pristine TiO2- and Gd (1, 2, and 3 %)-doped TiO2 nanoparticles were calculated to be 10.9, 9.2, 10.2 and 8.9 nm, respectively. The W-H plots also revealed average crystallite sizes in the range of 13.9, 16.6, 13.9 and 10.4 for pristine and Gd (1, 2, 3 %)-doped TiO2 nanoparticles. The lattice strain values for pristine and Gd (1, 2, and 3 %) doped TiO2 nanoparticles were computed as 0.00203, 0.00667, 0.0036 and 0.00262, respectively, from the W‒H plots. The average crystallite size was calculated to 9.2 nm from the TEM images using ImageJ software. The optical band gap values of pristine TiO2 and Gd (1, 2, and 3 %)-doped TiO2 nanoparticles were calculated to be 3.3, 3.23, 3.21 and 3.20 eV from the Kubelka–Munk function plot. The emission peaks of pristine and Gd(1,2,3 %) doped TiO2 nanoparticles were calculated as 3.2, 3.23, 3.26 and 3.32 eV from the photoluminescence spectra recorded at 330 nm photo excitation. The binding energies of the O1s, Ti2P and Gd4d peaks present in the survey scan of TiO2 nanoparticles doped with one weight percentage of Gd impurity were 528.79, 531.53, 457.53, 463.25 and 149.6 eV, respectively. The third-order nonlinear characteristics of the TiO2:Gd samples were probed using the ultrafast laser Z-scan technique. We observed that the density of bound excitons can be regulated by controlling the dopant concentration. The strong oscillatory interactions between photogenerated bound excitons, which act as dipole oscillators with large oscillating frequencies, were recorded using a single-beam femtosecond Z-scan. The third-order nonlinear susceptibility χ(3) for pristine and Gd(1,2,3 %)-doped TiO2 nanoparticles were calculated as 7.258 × 10-18, 9.4 × 10-18, 11 × 10-18 and 13 × 10-18 cm2/V2, respectively. The obtained results suggest that the thermal lensing phenomenon in nanostructured anatase TiO2 can be generated and effectively controlled using a band gap engineering technique. We determined that the small pump power in nonlinear media with controllable band fluctuations can produce large phase distortions in TiO2:Gd nanosystems. Our findings reveal that Gd doping induces controlled modification of the electronic structure of TiO2, leading to a tailored energy landscape for exciton formation and binding. These findings provide a novel approach for engineering systems of TiO2-based nanostructures for energy-efficient optical-limiting nanophotonic systems and optoelectronic-switching devices.

High-brightness betatron emission from the interaction of a sub picosecond laser pulse with pre-ionized low-density polymer foam for ICF research

Direct laser acceleration (DLA) of electrons in plasmas of near-critical density (NCD) is a very advancing platform for high-energy PW-class lasers of moderate relativistic intensity supporting Inertial Confinement Fusion research. Experiments conducted at the PHELIX sub-PW Nd:glass laser demonstrated application-promising characteristics of DLA-based radiation and particle sources, such as ultra-high number, high directionality and high conversion efficiency. In this context, the bright synchrotron-like (betatron) radiation of DLA electrons, which arises from the interaction of a sub-ps PHELIX laser pulse with an intensity of 1019 W/cm2 with pre-ionized low-density polymer foam, was studied. The experimental results show that the betatron radiation produced by DLA electrons in NCD plasma is well directed with a half-angle of 100–200 mrad, yielding (3.4 ± 0.4)·1010 photons/keV/sr at 10 keV photon energy. The experimental photon fluence and the brilliance agree well with the particle-in-cell simulations. These results pave the way for innovative applications of the DLA regime using low-density pre-ionized foams in high energy density research.

Interaction of intense ultrashort laser pulses with solid targets: A systematic analysis using first-principles calculations

Interaction of intense ultrashort laser pulses with solid targets: A systematic analysis using first-principles calculations

Attosecond and nano-Coulomb electron bunches via the Zero Vector Potential mechanism

The commissioning of multi-petawatt class laser facilities around the world is gathering pace. One of the primary motivations for these investments is the acceleration of high-quality, low-emittance electron bunches. Here we explore the interaction of a high-intensity femtosecond laser pulse with a mass-limited dense target to produce MeV attosecond electron bunches in transmission and confirm with three-dimensional simulation that such bunches have low emittance and nano-Coulomb charge. We then perform a large parameter scan from non-relativistic laser intensities to the laser-QED regime and from the critical plasma density to beyond solid density to demonstrate that the electron bunch energies and the laser pulse energy absorption into the plasma can be quantitatively described via the Zero Vector Potential mechanism. These results have wide-ranging implications for future particle accelerator science and associated technologies.

Efficient guiding and focusing of intense laser pulse using periodic thin slits

Slits have been widely used in laser–plasma interactions as plasma optical components for generating high-harmonic light and controlling laser-driven particle beams. Here, we propose and demonstrate that periodic thin slits can be regarded as a new breed of optical elements for efficient focusing and guiding of intense laser pulse. The fundamental physics of intense laser interaction with thin slits is studied, and it is revealed that relativistic effects can lead to enhanced laser focusing far beyond the pure diffractive focusing regime. In addition, the interaction of an intense laser pulse with periodic thin slits makes it feasible to achieve multifold enhancement in both laser intensity and energy transfer efficiency compared with conventional waveguides. These results provide a novel method for manipulating ultra-intense laser pulses and should be of interest for many laser-based applications.

High repetition rate coherent terahertz synchrotron radiation via self-amplified energy modulation

Coherent terahertz (THz) radiation sources based on a storage ring hold a significant future for generating high average power terahertz radiation, as the electron beam possesses a high revolution frequency. We propose a novel scheme to generate a high repetition rate coherent THz radiation leveraging the energy modulation self-amplification technology. In this scheme, utilizing the interaction of external intensity-modulated laser pulses with the electron beam can lead to a customized manipulation of the electron beam, such as a periodic longitudinal density modulation with a submillimeter scale for coherent THz radiation. Positively, it can propel the repetition rate when the peak power requirement of an external laser system is decreased. Thus, we employ a self-modulation method to enhance the initial weak energy modulation induced by the laser directly. In the meanwhile, the use of self-modulation can bypass the limitation that the bandwidth of a long modulator should be smaller than that of the external wideband laser source, which is necessary to shape the intensity envelope flexibly. The one-dimensional analytical description of electron longitudinal dynamic during the self-modulation process is given, which confirms the effective enhancement of the modulation at THz band. Three-dimensional time-dependent simulation results based on the parameters of Hefei light source-II show that the coherent THz radiation pulses with a repetition rate of 10 kHz can be generated. Published by the American Physical Society 2024

Quantum mechanical modeling of high-intensity laser pulse interaction with hydrogen atom with considering the magnetic field and polarization

In the study of the non-relativistic interaction between high-intensity femtosecond laser pulses and atoms, the influence of the magnetic field is commonly overlooked. This work investigates the effects of the magnetic field in the high-intensity few-cycle laser pulses with non-relativistic intensity of 3.5×1014W/cm2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$3.5 \ imes 10^{14} { }\\;\\;{\ ext{W}}/{\ ext{cm}}^{2}$$\\end{document} at the center wavelength of 800 nm on the high-order harmonic generation (HHG), attosecond pulse train (APT), isolated attosecond pulse (IAP), and the electron trajectory in the hydrogen atom, employing the numerical solution of the time-dependent Schrödinger equation in three dimensions (3D-TDSE). Two polarizations, linear and circular, are considered. A comparison with the scenario where the magnetic field is not considered shows that the magnetic field can apply significant corrections to the results. Particularly, considering the magnetic field for circular polarization can make the cutoff frequency of HHG coincide with the semi-classical relationship of ħωc=Ip+3.17Up\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\hbar {\\upomega }_{{\ ext{c}}} = {\ ext{I}}_{{\ ext{p}}} + 3.17{\ ext{U}}_{{\ ext{p}}}$$\\end{document}, a case that for circular polarization does not exist without considering the magnetic field. Moreover, accounting for the magnetic field leads to a reduction in the attosecond pulse duration for circular polarization for APT (360as\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$360{\ ext{ as}}$$\\end{document} versus 241as\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$241{\ ext{ as}}$$\\end{document}) and for IAP (834as\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$834{\ ext{ as}}$$\\end{document} versus 602as\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$602{\ ext{ as}}$$\\end{document}). Additionally, the difference in production efficiency of HHG and APT between linear and circular polarization is reduced by two orders of magnitude, when magnetic field is considered. Although considering the magnetic field complicates the electron trajectory, especially for circular polarization, however, our quantum model provides enhanced insight into how the interaction works, especially when and where the electron collides with the parent nucleus. In this case, the quantum mechanical modeling largely covers the huge difference of not considering the magnetic field in the results predicted by other works.

Spatiotemporal reshaping of femtosecond laser pulses on interaction with gas sheath at ionization saturation intensity regime

Interaction of intense ultrashort laser pulse with gases generates a transient spatiotemporal electron density distribution via field ionization, which may lead to the spatiotemporal reshaping of the pulse, viz., its beam profile, pulse width, etc. Here, we present an experimental study on ultrashort laser pulse interaction with argon gas sheath in an ionization saturation intensity regime (∼1015–1017 W/cm2). The present investigation has been performed using a 6 mJ, 1 kHz, and 55−60 fs Ti:Sapphire laser pulse interaction with a ∼2.5 mm long argon sheath. After the laser gas interaction, the laser spatial profile exhibits a multi-ring structure around a central maximum spot. Laser gas interaction parameters, such as laser intensity, gas pressure, etc., affect the ring pattern significantly. Under optimum parameter conditions, the laser pulse has two rings in spatial profile, and the pulse width of the central spot is self-compressed to ∼35 fs. A theoretical calculation reveals that the laser beam’s spatiotemporal profile evolves as it propagates inside the gas sheath. The calculation also demonstrates that the gas ionization profile plays a crucial role in the spatiotemporal reshaping and self-compression of the laser beam. The calculation also shows that the generation of concentric ring patterns in the spatial profile is mainly due to the ionization of argon atoms into Ar+, Ar2+, and Ar3+ species in the interaction region. Such self-compressed laser pulses with concentric ring beam profiles may be useful for high-harmonic generation and shorter attosecond pulse trains.

Synergic action of linear dispersion, second-order nonlinearity, and third-order nonlinearity in shaping the spectral profile of a femtosecond pulse transporting in a lithium niobate crystal

We present a detailed theoretical and numerical analysis on the temporal-spectral-spatial evolution of a high-peak-power femtosecond laser pulse in two sets of systems: a pure lithium niobate (LN) plate and a periodically poled lithium niobate (PPLN) plate. We develop a modified unidimensional pulse propagation model that considers all the prominent linear and nonlinear processes and carried out the simulation process based on an improved split-step Fourier transformation method. We theoretically analyze the synergic action of the linear dispersion effect, the second-order nonlinearity (2nd-NL) second-harmonic generation (SHG) effect, and the third-order nonlinearity (3rd-NL) self-phase modulation (SPM) effect, and clarify the physical mechanism underlying the peculiar and diverse spectral broadening patterns previously reported in LN and PPLN thin plate experiments. Such analysis and discussion provides a deeper insight into the synergetic contribution of these linear and nonlinear effects brought about by the interaction of a femtosecond laser pulse with the LN nonlinear crystal and helps to draw a picture to fully understand these fruitful optical physical processes, phenomena, and laws.

A computational model to understand the interaction of nanosecond pulsed laser with ultra-thin SiN[formula omitted] layer-coated silicon substrate

Nanosecond lasers can be used for the selective ablation of ultra-thin SiNx layer (80–100 nm) coated on a silicon substrate with applications in the fabrication of PERC solar cells. Experiments reveal that the ablation process can occur in different regimes with material removal in solid, liquid, vapor, and explosion forms. This study investigates the different regimes for single pulse ablation through a physics-based model developed using the finite volume method in Ansys Fluent. The model accounts for various physical phenomena, including laser heating, melting, thermal expansion, thermal decomposition, Marangoni convection, vaporization, plasma formation, melt expulsion, and phase explosion. Experiments were conducted using Nd: YVO4 laser (λ=532 nm, pulse duration = 50 ns), and the measured single pulse crater profiles are in excellent agreement with the model predictions over a broad range of laser fluence. Results show that the SiNx layer breaks due to the thermal expansion of the underlying silicon at lower fluences (3.05–3.35 J/cm2) in a very narrow range. Above this fluence range lies another narrow range (3.35–5.55 J/cm2) wherein the SiNx layer is thermally decomposed into silicon and nitrogen, and craters are formed due to Marangoni convection in the melt pool formed. Ablation due to vaporization occurs in a broad fluence range (5.55–8.4 J/cm2), causing deeper ablation depths and material deposition at the crater edge. At higher fluences (¿8.4 J/cm2), explosive boiling occurs due to homogeneous nucleation, resulting in much higher ablation depths (¿1.6μm), broader crater widths, and poor surface finish. This model provides an understanding of different material removal regimes in laser ablation of SiNx-coated silicon.

Spectrally resolved nonlinearities within a laser pulse in a single-scan and spectrometer-based nonlinear optical probing.

The intricate spectrally resolved optical nonlinearities resulting from a spectrally broad femtosecond Gaussian laser pulse have been unraveled using a single-scan and spectrometer-based nonlinear optical probing technique. The interaction of the broad femtosecond laser pulse with a strongly absorbing organic dye has unveiled a remarkably distinct nonlinear absorption behavior across the broad spectral window. The nonlinear absorption behavior unveils an unusual transition from the reverse saturation absorption (RSA) to the saturation absorption (SA) as we sweep the wavelength on both sides of the central wavelength of the excitation laser pulse. A competition between the band-filling and excited-state absorption results in such a dramatic switch-over from the RSA to the SA due to the variation of the intensity distribution across the Gaussian pulse spectrum. On the other hand, the nonlinear refraction studies dictate more over the constant Kerr-type positive nonlinear refractive indices across the entire laser pulse, with a pronounced contribution from the nonlinear absorption phase dominating at the center of the pulse. The presented technique establishes a robust and simple spectrometer-based technique that offers new, to the best of our knowledge, avenues for estimating optical nonlinearities for rapid nonlinear optical measurements.