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Quantum entanglement between the degrees of freedom encountered in the classical world is challenging to observe due to the surrounding environment. To elucidate this issue, we investigate the entanglement generated over ultrafast timescales in a bipartite quantum system comprising two massive particles: a free-moving photoelectron, which expands to a mesoscopic length scale, and a light-dressed atomic ion, which represents a hybrid state of light and matter. Although the photoelectron spectra are measured classically, the entanglement allows us to reveal information about the dressed-state dynamics of the ion and the femtosecond extreme ultraviolet pulses delivered by a seeded free-electron laser. The observed generation of entanglement is interpreted using the time-dependent von Neumann entropy. Our results unveil the potential for using short-wavelength coherent light pulses from free-electron lasers to generate entangled photoelectron and ion systems for studying spooky action at a distance. [ABSTRACT FROM AUTHOR]

Colorizing metals using micrometer and nanometer scale surface modifications has been vastly investigated and presents many advantages for applications across scientific and technological fields. By tuning the surface chemical composition or controlling its morphology, it is possible to produce a wide range of chromatic effects. Ultrafast laser processing presents here an interesting asset, as it allows to simultaneously provide chemical and morphological modifications at the micro‐scale in a single step. In this article, the composite colorization of copper surfaces with mW‐class average power deep ultraviolet (DUV) femtosecond laser pulses is demonstrated. The advantages of this setup are twofold: first, thanks to the increased absorption of copper in the DUV, the technique allows scaling down the requirement for laser power. Second, under ultrafast short‐wavelength illumination molecular oxygen bond‐breaks occur, enhancing the oxidation rate of the copper. The technique allows for highly controllable and efficient copper oxidation with the irradiation parameters. Taking these two effects into account, the generation of a wide spectrum of colors—from dark blue to shiny red—is demonstrated, and the role of the surface oxidation rate, the laser fluence, and laser scanning strategies in the colorization of copper surfaces employing DUV lasers is discussed. [ABSTRACT FROM AUTHOR]

Present study investigates the THz field generation from laser beat wave interaction with spherical nanoparticles (NPs) in presence of external magnetic field. A cluster of electrons and ions creates during laser interaction with spherical NPs and surface plasmon oscillations generate at surface of spherical cluster with characteristic frequency of ω p / 3 . Oscillatory current produces at beat-wave frequency (ω = ω 1 - ω 2) under the influence of laser imparted ponderomotive force. Oscillatory nonlinear current (J NL ) induces electromagnetic field (E THz / A 0) in THz frequency range. Field decentred (FDC) parameter δ is introduced in laser field profile that redistributes the laser energy in space; external magnetic field is applied in transverse direction. THz field amplitude is estimated with respect to terahertz frequency under the variation of FDC parameter δ , Magnetic field strength (B) and amplitude of the density perturbation (n q / n 0) . THz amplitude enhances significantly in presence of magnetic field with multiple resonance. Also, damping mechanism in plasmon oscillations of NPs can be controlled using laser intensity redistribution in polarization direction. [ABSTRACT FROM AUTHOR]

The formation of micro-scale tracks in the bulk of porous glass samples using femtosecond laser pulses was investigated, which is of interest for laser writing of active optical waveguides. It was ascertained that the impregnation of nanoporous glass with a bismuth nitrate solution effects the appearance of an orange luminescence band on excitation at 488 nm, which is intensified in the formed tracks. It is demonstrated that increasing the laser pulse energy to 200 nJ makes it possible to increase the phase contrast for tracks written in nanoporous glass containing bismuth, compared to tracks recorded in additive-free nanoporous glass. [ABSTRACT FROM AUTHOR]

Spin-polarized positron beams have widely been utilized in applications ranging from fundamental physical studies to material processing. Preparing highly polarized positron beams for accurate probing is a long-standing issue. Here, we put forward a method to produce ultra-relativistic polarized positrons with unprecedented purity in a femtosecond timescale employing a few-PW circularly polarized laser pulse. The fully spin-resolved QED Monte Carlo method is used for simulating the two successive QED processes during the interaction, i.e., nonlinear Compton scattering and nonlinear Breit–Wheeler pair production. As the photons emitted in a circularly polarized laser field are symmetrically polarized, the polarization of the intermediate gamma photon beam averages out to zero, which is advantageous for improving the polarization of positrons. Meanwhile, the moderate laser intensity suppresses the depolarization of the new-born positrons induced by radiation reaction effect. As a result, the polarization of the positrons can reach up to ≳ 90%, the highest among the laser-driven polarization schemes conceived hitherto. Furthermore, our method relaxes the requirement on laser intensity to few-PW level, offering a promising way of preparing polarized positrons with current-generation laser facilities. [ABSTRACT FROM AUTHOR]

In this paper, we demonstrate a SESAM mode-locked Tm:CaYLuAlO4 (a-cut) laser in the 2-μm spectral range. A birefringent filter (BF) is employed to shift the emission wavelength above 2 μm to support the stable mode locking through avoiding the structured water vapor absorption. Pulses as short as 288 fs are generated with a central wavelength of 2037 nm and an average power of 166 mW at a repetition rate of ~ 77.6 MHz. Moreover, wavelength tunable femtosecond laser with a tuning range from 2031.8 to 2081.1 nm is realized simply by rotating the birefringent filter around its surface normal. This work experimentally shows that birefringent filter is a simple and low-cost way to support the stable mode locking of Tm-bulk femtosecond lasers with an emission peak in the water vapor absorption region. [ABSTRACT FROM AUTHOR]

The beam self-cleaning phenomenon is theoretically predicted by the two-dimensional nonlinear Schrödinger equation, which describes self-focusing, and is observed in the case of femtosecond laser filamentation in the collimated regime of propagation. However, the impact of external focusing on the self-cleaning has not been investigated so far. In this paper we systematically study this impact in a wide range of focusing conditions. We show that the energy range, in which self-cleaning can be observed, shrinks monotonically with the numerical aperture growth at some point vanishing at all. [ABSTRACT FROM AUTHOR]

The pursuit of high‐resolution and advanced anti‐forgery technology has stimulated a growing demand for anti‐counterfeiting and encryption strategies with real‐time response and high security. Polarized patterns taking the advantage of high security, rapid response, simple operation, and great selectivity enable real‐time and non‐invasive detection by monitoring in different polarization directions. Here, a new strategy to design and fabricate the polarized CsPbBr3 quantum dot (QD) line arrays by femtosecond (fs) laser writing in a transparent glass matrix is proposed. The obtained line array structures endow isotropic CsPbBr3 QDs with macroscopic polarized emission with a polarization degree up to 0.189. Through programable design, the authors have created 2D and 3D polarized luminescent patterns made up of vertical and horizontal lines inside the glass for polarization‐sensitive optical anti‐counterfeiting patterns. The CsPbBr3 QD line arrays used in anti‐counterfeiting can be well maintained in the water environment. The successful demonstration of the laser writing CsPbBr3 QD polarization structures in glass highlights the versatility of anti‐counterfeiting and encryption. [ABSTRACT FROM AUTHOR]

Optical-range bulk diffraction nanogratings were fabricated via challenging direct inscription by ultrashort (femtosecond, fs) laser pulses inside heat-shrinkable polymers (thermoplastics) and VHB 4905 elastomer. The inscribed bulk material modifications do not emerge on the polymer surface, being visualized inside the materials by 3D-scanning confocal photoluminescence/Raman microspectroscopy and by the multi-micron penetrating 30-keV electron beam in scanning electron microscopy. The laser-inscribed bulk gratings have multi-micron periods in the pre-stretched material after the second laser inscription step, with their periods continuously reduced down to 350 nm on the third fabrication step, using thermal shrinkage for thermoplastics and elastic properties for elastomers. This three-step process allows facile laser micro-inscription of diffraction patterns and their following controlled scaling down as a whole pattern to pre-determined dimensions. In elastomers, utilizing the initial stress anisotropy, the post-radiation elastic shrinkage along the given axes could be precisely controlled until the 28-nJ threshold fs-laser pulse energy, where elastomer deformation ability is dramatically reduced, producing wrinkled patterns. In thermoplastics, the fs-laser inscription does not affect their heat-shrinkage deformation up to the carbonization threshold. The measured diffraction efficiency of the inscribed gratings increases during the elastic shrinkage for the elastomers and slightly decreases for the thermoplastics. High 10% diffraction efficiency was demonstrated for the VHB 4905 elastomer at the 350 nm grating period. No significant molecular-level structural modifications were observed by Raman micro-spectroscopy in the inscribed bulk gratings in the polymers. This novel few-step method paves the way for facile and robust ultrashort-pulse laser inscription of bulk functional optical elements in polymeric materials for diffraction, holographic and virtual reality devices. [ABSTRACT FROM AUTHOR]

The processes of laser dispersion of materials for high-performance generation of colloidal nanoparticles in liquids have been considered. Various laser and material parameters affecting this process have been studied. Efficiencies and ergonomics of the generation of colloidal nanoparticles with the help of laser systems having nano-, pico-, and femtosecond pulse durations have been compared using optical and mass criteria by the example of laser ablation of a chemically inert model material (gold) in distilled water without the use of chemical stabilizers. The main characteristics of gold and silver nanoparticles obtained by ablation in water using pulsed laser radiation of different durations have been comprehensively compared. The types of colloidal interactions between nanoparticles in aqueous media have been discussed, and the contributions of structural and ion-electrostatic interactions to the long-term stability of gold and silver nanoparticle dispersions have been analyzed. [ABSTRACT FROM AUTHOR]

In this study, we analyzed the X-ray fluorescence of the multi-layer material with a laser-induced X-ray and electrons. The laser plasma-based sources were generated by the femtosecond Ti: sapphire laser source, and we optimized sources for the X-ray fluorescence measurement. The laser-induced X-ray fluorescence of three types of stainless steel, copper-covered stainless steel and three types of Korean 10 Won coins were measured using a compact laser with relatively low intensity. Using the difference in penetration depth between X-rays and electrons, the surface and interior of multi-layer materials can be analyzed simultaneously. By combining these two complementary sources, we can provide valuable information about the surface and interior of multi-layer materials even with the compact laser. [ABSTRACT FROM AUTHOR]

This paper presents results of femtosecond laser micromachining of a transparent glass-ceramic in the Li2O–Al2O3–SiO2 system with a near-zero linear thermal expansion coefficient in the thermal and athermal regimes. Electron microscopy and electron diffraction data confirm complete amorphization of nanocrystals of β-eucryptite-like solid solutions under the effect of laser pulses. Using quantitative phase microscopy, we have evaluated refractive index changes in individual laser-written tracks. In the athermal regime at a pulse repetition rate of 10 kHz, complete glass-ceramic amorphization leads to a decrease in the refractive index of the material (Δn = −0.0035) in the laser treatment region, which opens up the possibility of using direct laser writing of channel waveguides in a thermally stable glass-ceramic matrix. [ABSTRACT FROM AUTHOR]

We investigate the evolution mechanisms of the laser-induced periodic surface structures (LIPSS) and quasi-periodic grooves that are formed on the surface of monocrystalline silicon (mono-Si) when exposed to femtosecond laser radiation of different pulse duration, state of polarization, and fluence. The conditions required for producing LIPSS-free complex micro-ridge patterns are elaborated. The LIPSS evolution mechanism is explained in terms of scattering/interference-based phenomena. To establish the basis for our interpretation, single femtosecond pulses of different pulse durations are irradiated on mono-Si. The absence/appearance of LIPSS rudiments is explained in the context of spectral bandwidth and the associated effects on the intensity of the central wavelength. Shorter fs pulses of a wider bandwidth are employed to induce LIPSS-free micro-ridge patterns. It is demonstrated that the resultant micro-ridge patterns depend on the laser fluence distribution and can be manipulated through laser polarization. The curved morphology of LIPSS rudiments and the evolution mechanism of low- and high-spatial frequency LIPSS, i.e., LSFL and HSFL, are discussed. Finally, it is demonstrated that the consolidated quasi-periodic grooves result from HSFL welding together groups of LSFL. Although our findings are based on fs laser interaction with mono-Si, the results can also be applied to many other materials. [ABSTRACT FROM AUTHOR]

Multiphoton photopolymerisation (MPP), also known as 3D nanoprinting, was studied using a wavelength-tunable femtosecond laser. The possibility of using any colour of the spectrum from 500 to 1200 nm with a fixed pulse width of 100 fs revealed an interplay of photophysical mechanisms more delicate than just two-photon photopolymerisation. An effective order of absorption, i.e. the X-photon absorption, as well as optimal exposure conditions were assessed for photosensitised and pure SZ2080TM pre-polymer. The tunability of wavelength greatly influenced the dynamic fabrication window (DFW), optimised conditions resulting in a 10-fold increase. Furthermore, a non-trivial energy deposition by X-photon absorption was noted with an onset of a strong lateral size increase at longer wavelengths and can be understood as due to reaching epsilon-near-zero conditions. Such a control over the voxel aspect ratio and, consequently, the photopolymerised volume, may boost 3D nanoprinting efficiency. Overall, the results reveal wavelength being an important degree of freedom to tailor the MPP process and, if optimised, benefiting broad applications in areas of micro-optics, nanophotonic devices, metamaterials and tissue engineering. [ABSTRACT FROM AUTHOR]

The features of nonlinear propagation of high-intensity pulses in the short-wavelength infrared range in extended one-dimensional waveguide arrays with different spatial periods, formed in fused silica by laser writing, are studied. More than tenfold self-compression of femtosecond pulses up to a duration of several periods of the light field is experimentally observed. [ABSTRACT FROM AUTHOR]

H13 steel with a sub‐millimeter‐order periodic laminate structure is fabricated using the laser powder bed fusion process by changing the input energy periodically, and the effect of heat treatment on the hardness distribution of the alloy is examined. When the as‐built specimen is directly tempered at 550 °C to induce secondary hardening, the hardness values at the matrix area of the specimen, which average 638 HV under the as‐built condition, increase to an average of 685 HV, whereas those of intermediate areas, which initially average 658 HV, reach an average hardness of 722 HV, which is higher than that of the matrix area even under the tempered condition. Consequently, the hardness distribution maintains the initial trend, wherein the hardness varies periodically depending on the area, exhibiting a shift toward higher hardness values under the tempered condition. The factors affecting the hardness and tempering behavior are investigated by analyzing the phase constituents and microstructural evolution. The tempered specimen comprises α′‐martensite, indicating that retained austenite present in the as‐built microstructure is almost completely decomposed. At the nanolevel, only V segregates at the lath boundaries under the as‐built condition, while various metallic carbides are formed at the lath boundaries after tempering. [ABSTRACT FROM AUTHOR]

High-repetition-rate ultrafast lasers are needed for diverse applications. Harmonic modelocking, where multiple identical, equidistant pulses circulate in the cavity, reaches beyond the practical limitations of reducing the cavity length. However, it suffers from stochastic deviations that manifest as supermodes in the radio-frequency spectrum and difficulties in maintaining the same harmonic state, often coupled with trade-offs in pulse energy, duration, or noise performance. Here, we first show that deviations in the temporal positions of the pulses contribute disproportionately more to the supermodes than deviations in their amplitudes. Then, we argue that these fluctuations are analogous to those of trapped Brownian particles. This analogy reveals that supermodes are suppressed by stronger spectral filtering, which corresponds to fluid viscosity, and higher pulse energy reduces the noise, akin to lower temperature. Guided by this intuitive picture, we construct a Yb-fibre laser incorporating strong filtering and high intracavity energies by limiting nonlinear polarisation evolution to a short section of ordinary fibre. The rest of the all-fibre cavity comprises polarisation-maintaining fibre, which additionally improves environmental robustness. We report record-high supermode suppression ratios, reaching 80 dB, excellent long-term and environmental stability, and pulse energy, duration, and noise characteristics that are similar to fundamentally modelocked lasers. [ABSTRACT FROM AUTHOR]

In this work lasers with micro-, nano-, pico- and femtosecond pulse durations were used to clean atmospheric corrosion products from the fragments of a 19th-century lead outdoor sculpture. The state of the surface was studied by optical microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy and scanning electron microscopy. It was shown that for all lasers used there is no self-limiting cleaning effect, and the metal damage threshold is lower than the corrosion removal threshold. Using the XPS method, it has been demonstrated that the effect of turning a metallic lead surface blue after irradiation is associated with an interference effect in the PbO film. Raman spectroscopy indicated no phase changes in the corrosion layer after laser cleaning with 8 ns, 75 ps and 100 fs pulses, which makes these lasers useful for the layer-by-layer cleaning of archaeological objects. [ABSTRACT FROM AUTHOR]

High-performance 86 µJ, 11.2 fs pulses with a spectrum range of 800-1050 nm are generated based on 1030 nm, 190 fs Yb femtosecond pulses by using multi-plate-based spectral broadening and filtering. Taking advantage of single beam configuration, the obtained pulses have excellent power and spectral stabilities. Since the output spectrum is obtained by spectrally filtering the broadened components, the temporal contrast of the output pulses is enhanced by at least four orders of magnitude. Together with the robust and simple setup, the proposed method is expected to be a competitive option for the generation of seed pulses for 10s-100s petawatt lasers. [ABSTRACT FROM AUTHOR]

THz radiation through a novel scheme based on a three-pulse configuration in two-dimensional ordinary and extraordinary modes was investigated. The electromagnetic radiation driven by the linear and nonlinear current density created by the laser-induced plasma mechanism has been evaluated. The numerical findings of the present study show that the electric field of THz radiation is significantly improved compared to the two-color scheme if the third harmonic is included. The asymmetric three-color femtosecond laser fields can be used to control the polarization state, radiation power, and the directivity of the THz radiation. With adjustable time delays between pulses, the polarization controllability of THz radiation from plasma, based on experimental conditions, can be achieved. With this scheme, not only tuning to circularly polarized THz radiation is feasible, but also linear or elliptical polarization can be realized by adjusting time delays. The effects of different laser profiles and wavelengths on ionization rate are considered. Variation of the electric field of the generated THz waves for both ordinary and extraordinary modes of photocurrent mechanism is examined numerically for various spatial laser profiles. The study indicates that a laser pulse profile can be used to control THz radiation. [ABSTRACT FROM AUTHOR]

Femtosecond laser machining of materials has transformed into a mature high‐precision technology, giving access to a wide range of applications. Yet, for a complete exploitation of its full potential, a detailed knowledge of the complex laser–matter interaction processes is required. For the case of the application‐relevant material steel, a complete study of the electron dynamics and material transformation upon single laser pulse irradiation (800 nm, 120 fs) is reported. Detailed analysis of the obtained time‐ and fluence‐dependent reflectivity map reveals that ultrafast electron heating during the pulse is directly followed by energy transfer to the lattice within a few picoseconds, reaching fluence‐dependent peak temperatures from below melting threshold to above the boiling point. Moreover, an innovative approach to obtain the ultrafast‐evolving 3D structure of a femtosecond laser excited material is reported, unraveling the dynamics of complex processes as melting, ablation, and solidification. Combined with modeling, the evolving optical properties, multilayer structure, and expansion velocities can be precisely determined. The information obtained from this study will contribute to further increase the achievable precision and wealth of structures that can be produced by designing efficient pulsed energy deposition schemes for selective re‐excitation of the material. [ABSTRACT FROM AUTHOR]

This work demonstrates for the first time the formation of nanogratings inside Barium Gallo-Germanate (BGG) glasses using femtosecond laser direct writing. These heavy oxide glasses, with a characterized transparency window up to 6 μ m, along with the polarization sensitive birefringent nanostructures induced by femtosecond laser, offer an excellent platform for the development of mid-Infrared photonic applications. The fabricated glasses, containing both rare earth elements (Gd, Y) and transition metals (Zn, Ta), are directly compared to amorphous GeO 2 and commercial alumino-germanate (Corning-9754) glasses commonly used in this field. The nanogratings processing window in each glass was investigated by varying laser parameters (pulse duration, energy, repetition rate), and electron microscopy imaging directly evidenced the porous nanostructures. Among the results, a strong form birefringence in 8% ZnO containing BGG glass, e.g., up to −0.029 ± 0.001, was reported. Finally, birefringent embedded Fresnel GRIN plates were directly written in a BGG glass, to demonstrate the functionalization potential of these materials. [ABSTRACT FROM AUTHOR]

Two methods of laser acceleration of protons/deuterons for initiation of nuclear reactions in the so-called pitcher-catcher scheme aimed at production of medical isotopes and obtaining short neutron pulses are studied using the combined particle-in-cell (PIC) and Monte Carlo (GEANT4) numerical simulation. It is demonstrated that the pulse repetition frequency on the order of 100 Hz is required for obtaining a medical dose of the radionuclids used in the positron-emission tomography (PET) in the case of ion acceleration from a thin foil most efficient in the forward direction by means of a femtosecond laser pulse with energy of several joules. In the case of ion acceleration from a low-density target most efficient in the transverse (radial) direction, lasers pulses of substantially higher energy and picosecond pulse duration have to be used, which allows one to increase the yield of radionuclids per unit deposited energy. In the process, the pulse repetition frequency must be at the level of 1–10 Hz. Laser generation of neutrons by means of reactions initiated by accelerated ions obtained using thin foils or targets of lower density is simulated, and the possibility of obtaining 108 neutrons per laser pulse using 3-J laser pulses is demonstrated. [ABSTRACT FROM AUTHOR]

Explicit visualization of different components of surface plasmon polaritons (SPPs) propagating at dielectric/metal interfaces is crucial in offering chances for the detailed design and control of the functionalities of plasmonic nanodevices in the future. Here, we reported independent imaging of the vertical and horizontal components of SPPs launched from a rectangular trench in the gold film by a 400-nm laser-assisted near-infrared (NIR) femtosecond laser time-resolved photoemission electron microscopy (TR-PEEM). The experiments demonstrate that distinct imaging of different components of SPPs field can be easily achieved by introducing the 400-nm laser. It can circumvent the risk of sample damage and information loss of excited SPPs field that is generally confronted in the usual NIR laser TR-PEEM scheme. The underlying mechanism for realizing distinct imaging of different components of the SPPs field with two-color PEEM is revealed via measuring the double logarithmic dependence of photoemission yield with the 800-nm and 400-nm pulse powers of different polarizations. Moreover, it is found that the PEEM image quality of the vertical and horizontal components of the SPPs field is nearly independent of the 400-nm pulse polarization. These results pave a way for SPPs-based applications and offer a possible solution for drawing a spaceâ€"time field of SPPs in three dimensions. [ABSTRACT FROM AUTHOR]

The fabrication of polymer–metal hybrids in an additive process makes it possible to further improve the geometrical and material adaption in a multi-material design. In this work, PLA is fabricated through a fused filament fabrication process on AlSi10Mg structures manufactured by laser powder bed fusion. The mechanical connection is realised by form fit, for which different geometries are examined through tensile tests. Deep penetration of the PLA into the metallic structures is achieved by optimisation of the process parameters. The penetration depth is assessed through the use of micro-computed tomography. Finally, the interplay of mechanisms leading to a firm connection is discussed. [ABSTRACT FROM AUTHOR]

The broadband laser induced white emission (LIWE) spectra of NdAlO3 nanocrystals in vacuum, air, and liquid N2 were explored. In particular, their dependence on excitation laser power was investigated. It was found that the LIWE spectra intensity increased exponentially the with laser power above the excitation threshold in all three cases. The process for NdAlO3 nanocrystals was discussed in terms of multiphoton ionization assisted by ejection of hot electrons. Two differences were observed depending on the conditions: the number of photons involved in the emission was higher in liquid N2 due to additional multiphoton ionization contribution of N2. Also, threshold value for LIWE showed an increasing behavior in air and liquid N2, discussed in terms of relative permittivity and thermal dissipation. [ABSTRACT FROM AUTHOR]

Limited by the difficulty in acceleration synchronization, it has been a long-term challenge for on-chip dielectric laser-based accelerators to bridge the gap between non-relativistic and relativistic regimes. Here, we propose a laser-based accelerators based on a spatio-temporal coupling controlled laser pulse, which enables the acceleration of a non-relativistic electron to a sub-MeV level in a single acceleration structure (chirped spatial grating). It provides high precision temporal and spatial tuning of the driving laser via dispersion manipulation, leading to a synchronous acceleration of the velocity increasing electrons over a large energy range. Additionally, the spatio-temporal coupling scheme is a general method and can be extended to driving fields of other wavelengths such as terahertz pulses. Our results bring possibilities to MeV-scale portable electron sources and table-top acceleration experiments. A long-standing challenge for on-chip dielectric laser-based accelerators is to bridge the gap between nonrelativistic and relativistic regimes. Here, an all-optical acceleration scheme is proposed that maximises the electron-field interaction length, and hence the acceleration, by spatio-temporal pulse shaping. [ABSTRACT FROM AUTHOR]

The current paper has been presented to illustrate the thermoelastic vibration of a rotating microbeam based on generalized thermoelasticity theory, taking into account Euler–Bernoulli's assumptions. Using Hamilton's principle, the equation of motion of the initially stressed rotating microbeams has been derived. The microbeam is exposed to femtosecond laser pulses and sinusoidal varying heat. The Laplace transform technique is applied to obtain an analytical solution to the field variables. The influence of properties of various parameters, such as axial load, laser pulse duration, angular velocity, and material variation on the thermal and elastic waves of the rotating microbeam has been displayed graphically and discussed in detail. [ABSTRACT FROM AUTHOR]

[Display omitted] • Development of periodic structured surface with compressive residual stress on Ti6Al4V by Ti: sapphire laser irradiation. • Stress-induced grain refinement of Ti: sapphire laser irradiated Ti6Al4V. • Improved nano hardness and Young's modulus of the structured surface. • Improved tribocorrosion resistance of Ti6Al4V due to laser surface structuring. In the present study, the effect of ultrafast laser surface structuring of Ti6Al4V (using a Ti: Sapphire laser with a pulse duration of 100 fs and 3000 fs) on its surface topography, nanomechanical properties, tribocorrosion property, and bioactivity has been undertaken. Surface structuring leads to defect-free periodic surface structures with shockwave-induced compressive residual stresses and grain refinement (subgrain size of 5.2 µm) as compared to as received Ti6Al4V (26 µm). There is a significant enhancement in nano hardness (5600–5800 MPa) and Young's modulus (139 – 148 GPa) as compared to as received Ti6Al4V ((nano hardness of 3800 MPa), (Young's modulus of 117 GPa)) due to laser surface structuring. The tribocorrosion kinetics were significantly reduced in laser surface structured Ti6Al4V as compared to as received one. The individual influence of tribocorrosion property was established. A detailed microstructural study and immersion studies showed the presence of a higher fraction of calcium phosphate deposition in surface-structured samples (0.0432–0.0461 mg/cm2 after 7 days) as compared to as received Ti6Al4V (0.018 mg/cm2 after 7 days). The presence of hydroxyapatite has been confirmed by X-ray photoelectron spectroscopic analysis. [ABSTRACT FROM AUTHOR]

Over the last decade, lasers have been gradually employed for Si wafer dicing to replace blade dicing. Laser dicing has the potential to replace blade dicing as the future generation ultrathin wafer singulation method as it enables higher cutting speed, lower damage, and smaller kerf width but various technical challenges still remain to be resolved. In this article, laser ablation and dicing of Si wafers are reviewed in terms of the physics of laser-material interaction based on nanosecond, picosecond, and femtosecond pulse durations. The effects of various laser settings, dicing process parameters, and material factors on ablation rate, ablation precision and quality, and die fracture strength are discussed in detail. With the increasing usage of Cu stabilization layer on the backside of ultrathin Si wafers, we also review laser-material interaction in Cu and elaborate on recent findings on the effects of laser dicing through Si and Cu simultaneously on the microstructural and fracture strength properties of the die. Various approaches to improve the ablation rate, ablation quality, and die fracture strength are discussed. • Laser dicing of thin Si wafers is gaining more importance in the semiconductor industry because of its cost-effectiveness compared to conventional blade dicing. • Understanding laser ablation mechanisms remains a huge challenge because of the complexity of the processes taking place, the variety of species involved, and the range of length and time scales covered. • Many challenges remain for laser dicing of Si wafers primarily in three critical areas, i.e., ablation rate, ablation precision and quality, and die fracture strength. • Optimization of the ablation rate, ablation quality, and die fracture strength will require thorough consideration of all the influencing laser and process parameters in order to meet the requirements of the end product applications. [ABSTRACT FROM AUTHOR]

The great potential of high‐intensity lasers to generate quantum beams for material analysis is highlighted by introducing some representative examples, including laser electron acceleration for ultrafast electron diffraction/deflectometry and laser terahertz surface wave generation. We have demonstrated that short electron pulses can be generated by intense femtosecond laser pulses. The pulse duration is as short as 100 fs, which is superior to that obtained using conventional accelerators. These short electron pulses are applicable to not only to the study of materials but also the observation of laser–matter interaction phenomena. © 2021 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC. [ABSTRACT FROM AUTHOR]

We have proposed a scheme to increase the ultra-intense femtosecond laser absorption efficiency by using carbon aerogel targets. Particle-in-cell simulations show that, compared to a homogeneous target of the same density, the carbon aerogel target can significantly enhance the laser absorption efficiency, and the maximum laser absorption efficiency can reach 88%. Such high absorption efficiency can be attributed to the porous structure and larger surface area of carbon aerogel than ordinary materials, which allows the laser to enter more of the target and interact more fully with the particles inside rather than being reflected off the surface. By studying the interaction between the laser and the carbon aerogel targets, we found that both the nanoparticle diameter and porosity have great effects on the laser absorption efficiency, which is enhanced significantly as the nanoparticle diameter and porosity increase. Such carbon aerogel targets should have significant applications in the fields of laser generation of x rays and high energy density physics. [ABSTRACT FROM AUTHOR]

Laser direct writing is a widely employed technique for 3D, contactless, and fast functionalization of dielectrics. Its success mainly originates from the utilization of ultrashort laser pulses, offering an incomparable degree of control on the produced material modifications. However, challenges remain for devising an equivalent technique in crystalline silicon which is the backbone material of the semiconductor industry. The physical mechanisms inhibiting sufficient energy deposition inside silicon with femtosecond laser pulses are reviewed in this article as well as the strategies established so far for bypassing these limitations. These solutions consisting of employing longer pulses (in the picosecond and nanosecond regime), femtosecond‐pulse trains, and surface‐seeded bulk modifications have allowed addressing numerous applications. [ABSTRACT FROM AUTHOR]

With the development of femtosecond (fs) laser technology, an fs laser pulse with 10s of Joule, even 100s of Joule energy is available and the focused laser intensity can be expected to induce the pure Coulomb explosion of the cluster with a much larger average radius than before. Meanwhile, the production of gas cluster with an average radius of upto 10s of nanometer has been possible. In this case, it is necessary to reinvestigate the feasibility of 109 n/shot neutron yield for the practical application in the intense fs laser-driven nuclear fusion. In this work, the neutron yield from the explosions of the D2 clusters of 6–20 nm average radius at the 0.5–100 J pulse energy and the CD4 clusters was investigated theoretically. It is found that the optimum neutron yield of 109 n/shot can be obtained at the laser energy and the cluster radius currently available. However, a clustered-gas jet with a large cross-section is demanded to match the proper plasma diameter. [ABSTRACT FROM AUTHOR]

We show that generation of strong magnetic field filaments due to Weibel instability accompanies the hole-boring ion acceleration by a circularly polarised laser pulse. The magnetic field confines energetic protons accelerated from hole boring in high density collimated jets. A part of energetic protons are reaccelerated by the electric field and focused by the magnetic field generated from the jets. As a result, highly collimated proton jets with high cutoff energy can be produced. [ABSTRACT FROM AUTHOR]

The reconnection rate in relativistic magnetic reconnection driven by two relativistic intense femtosecond laser pulses is investigated using three-dimensional particle-in-cell (PIC) simulation. As the drive is enhanced, the current sheet is narrowed, and the reconnection rate is weakened. A new theoretical model is given to explain the rate observed in the PIC simulation. In addition, multi-scale reconnection is studied by setting a different ion mass in the simulation code. For , the current sheet is only at the electron scale, and only electron outflow jets are observed, which are super ion Alfvénic and close to the electron's Alfvénic speed. The lengths of the electron outflow jets reach 100–200 times the length of the electron gyroradius and beyond the ion gyroradius. However, when , more ions are coupled to electrons during the laser and plasma interaction, there are also electron outflow jets and no ion outflow jets in the current sheet, and the electron outflow jets are embedded in a wider ion-scale current layer. [ABSTRACT FROM AUTHOR]

In this study, the effects of hydrostatic pressure, temperature, and high-frequency intense laser field on the nonlinear optical properties of an asymmetric GaAs/AlGaAs double quantum well was theoretically investigated. For this, firstly, the energy eigenvalues and eigenfunctions of the system have been obtained using the effective-mass and parabolic band approximation. Later, the nonlinear optical properties of the structure are calculated using the compact-density matrix approach. The obtained numerical results show that when the magnitude of the intense laser field applied to the structure is increased, the amplitudes of both the total optical absorption coefficients (TOACs) and the relative refractive index changes (RRICs) peaks increase and shift towards higher energies. In addition, it was also observed that the increase in temperature had a similar effect on the TOACs and RRICs with the intense laser field, whereas the increase in hydrostatic pressure has an opposite effect. [ABSTRACT FROM AUTHOR]

As a femtosecond terawatt laser pulse propagates along a positive density gradient within a stratified plasma column, it drives a low-frequency electromagnetic wake wave, the period of electron fluid oscillations in the wake gradually shrinking. Phase velocity of the wake promptly exceeds the vacuum speed of light, setting in near-forward emission of terahertz Cherenkov radiation. As the wake accelerates further, the Cherenkov emission ray rotates by 180∘. Emission from a given plasma locality is sustained for a finite interval of time, in the middle of which the wake experiences a 'reversal,' its phase velocity becoming singular and changing sign (Zhang C J et al 2017 Phys. Rev. Lett. 119 064801) At this instant, the electromagnetic energy flows at 90∘, the emission power reaching its peak. After the reversal, the wake keeps radiating into the rear hemisphere until its phase velocity becomes subluminal. Experimentally capturing evolution of the Cherenkov signal may thus shed light onto the plasma wake dynamics. Far away from the plasma, the radiation fills an expanding, almost spherical shell, the shell thickness increasing with an increase in the observation angle. The length of the terahertz signal sampled in the wave zone thus ranges from zero (forward emission) to a few tens of picoseconds (backward emission). The signal is positively chirped, its frequency increasing from the Langmuir frequency at the foot of the column to the Langmuir frequency at the top. Theoretical estimates for the regimes involving 10 TW-class drive pulses promise a few-kW emission power; the energy conversion efficiency, from optical to terahertz, of order 10−7; and an MV m−1-scale electric field strength centimeters away from the plasma. [ABSTRACT FROM AUTHOR]

In this paper, a non-reciprocal writing effect is proposed on the silicon by a femtosecond laser with tailor of temporal chirp. The induced structures which belong to the written lines with two opposite scans show obvious difference in the ablated regions. The grating compressor of a laser system is controlled to change the temporal chirp so as to flip the direction of the pulse front tilt, which results in 2 types of induced structures exchanging between two opposite scans. We assume, during the laser scans along the pulse front tilt, there may have a snowplow effect on the excited free electrons, leading to an asymmetrical electrical field distribution around the focal area. This process could further boost an ionization efficiency in the next pulse irradiation as well as make the induced structures grow faster. Current result possibly offers a new route to control the density of free electrons excited when femtosecond laser interacts with silicon wafer. [ABSTRACT FROM AUTHOR]

Highly sensitive and cost-effective flexible piezoresistive sensors are pursued as essential components of electronic skin (e-skin) for a variety of applications such as soft robotics and body prosthesis. A common strategy for achieving high sensitivity of these sensors is to fabricate their electrode material with complex 3-D microstructures, but manufacturing cost-effective micro-structured sensors with high reliability and reproducibility is a challenge. Herein, a robust approach for producing high-reproductive microstructured polydimethylsiloxane (PDMS) films composing the sensors is proposed, based on silicon molds with a honeycomb-like architecture fabricated rapidly and cost-effectively at a standoff distance by femtosecond laser pulses in the self-channeling regime. Single-walled carbon nanotubes (SWNTs) are embedded in the micro-structured PDMS films composing sandwich-structural flexible piezoresistive sensors. The sensing devices exhibit good performance with high sensitivity, fast response time, and excellent stability and are used with success for the detection of hand motion pressure and blood pressure at the wrist, thus showing a great potential as components of e-skin for detection of various human motions. [ABSTRACT FROM AUTHOR]

Dust explosion hazards can be analyzed by various explosion parameters, which are known to depend on the particle size distribution of combustible dust. Literature has evidenced the dispersion system in laboratory apparatus (e.g., 20-L chamber) breaks the original dust into smaller sizes. Such unexpected particle breakage can lead to misleading explosion results which may exaggerate the actual hazards. This study develops a novel solution to identify combustible particle breakage by exploiting dry dispersion laser diffraction technology. Nine samples were dispersed under different levels of energy in a particle size analyzer. Serious particle breakage is confirmed if the tested particle size decreases significantly with increasing dispersion pressure. Eight particle size parameters were plotted to derive quantitative pressure titration curves. A larger average slope in percentage decreases of D 10 , D 50 , and D 3,2 represents a higher particle breakage tendency. The characterization results are well correlated to previous breakage classification in the 20-L chamber. [Display omitted] • A new approach via laser diffraction is proposed to identify particle breakage due to dispersion. • Results are well correlated to previous particle breakage classification performed in the 20-L chamber. • Combustible dusts can be categorized into three breakage classes: BCI, BCII and BCIII. • It is suggested to apply the approach during the stage of sample characterization in laboratory tests. [ABSTRACT FROM AUTHOR]

Ultrafast laser systems typically employ complicated systems for varying their pulse length (duration) such as an ultrafast IR mode-locked laser used at the Schlesinger Compact Accelerator Center at Ariel University. The laser is an Astrella manufactured by Coherent generating an 800 nm pulse. The pulse duration can be varied from 10 ps to 35 fs using a remote-controlled grating-based compressor. In order to measure the time duration of the pulse, an automated compact autocorrelator was designed and developed. The laser is mainly used to extract electrons from a photo-cathode using dual BBO frequency tripling system, providing a UV (266 nm) ultra-short pulse. The electrons are formed into a beam, which is used to generate a THz FEL. Using an fs-level UV pulse, the extracted electron beam is unstable, resulting in high space-charge effects, high emittance values, and lowered radiation power dramatically. For this reason, we aim to stretch the UV pulse to a ps level. We study here an applicative method that uses dispersive materials. This method is convenient, compact, and can be easily installed. However, ultrafast lasers can suffer from high dispersion orders. Therefore, we study the contribution of the third and fourth orders of dispersion using analytical and numerical methods. Furthermore, our analysis takes into account the self-phase modulation effect when intense lasers are used. An experimental measurement is executed to confirm our numerical results, and a comparison between the experimental and simulation results is presented. [ABSTRACT FROM AUTHOR]

Within the framework of the Markov (factorization) approximation based on the factorization of the total density matrix of a system of an atom, a laser field, and an electromagnetic vacuum field, the spectrum of spontaneous photon emission when atoms are irradiated by a strong laser field is calculated. [ABSTRACT FROM AUTHOR]

SwissFEL is a compact, high-brilliance, soft and hard X-ray free electron laser (FEL) facility that started user operation in 2019. The facility is composed of two parallel beam lines seeded by a common linear accelerator (LINAC), and a two-bunch photo-injector. For the injector, an innovative dual-photocathode laser scheme has been developed based on state-of-the-art ytterbium femtosecond laser systems. In this paper, we describe the performance of the SwissFEL photocathode drive lasers (PCDLs), the pulse-shaping capabilities as well as the versatility of the systems, which allow many different modes of operation of SwissFEL. The full control over the SwissFEL electron bunch properties via the unique architecture of the PCDLs will enable in the future the advent of more-advanced FEL modes; these modes include, but are not restricted to, the generation of single or trains of sub-femtosecond FEL pulses, multi-color FEL and finally, the generation of fully coherent X-ray pulses via laser-based seeding. [ABSTRACT FROM AUTHOR]

We study and discuss electron acceleration in vacuum interacting with fundamental Gaussian pulses using specific parameters relevant for the multi-PW femtosecond lasers at ELI-NP. Taking into account the characteristic properties of both linearly and circularly polarized Gaussian beams near focus we have calculated the optimal values of beam waist leading to the most energetic electrons for given laser power. The optimal beam waist at full width at half maximum correspond to few tens of wavelengths, Δw0 = {13, 23, 41}λ0, for increasing laser power P0 = {0.1, 1, 10} PW. Using these optimal values we found an average energy gain of a few MeV and highest-energy electrons of about 160 MeV in full-pulse interactions and in the GeV range in case of half-pulse interaction. [ABSTRACT FROM AUTHOR]

We study the influence of the polarization states of ionizing femtosecond two-color pulses on the emitted terahertz radiation in gases. A local-current model and plane-wave evaluations justify the previously-reported impact on the THz energy yield and a (almost) linearly-polarized THz field when using circularly-polarized laser harmonics. For such pump pulses, the THz yield is independent of the relative phase between the two colors. When the pump pulses have same helicity, the increase in the THz yield is associated with longer ionization sequences and higher electron transverse momenta acquired in the driving field. Reversely, for two color pulses with opposite helicity, the dramatic loss of THz power comes from destructive interferences driven by the highly symmetric response of the photocurrents lined up on the third harmonic of the fundamental pulse. While our experiments confirm an increased THz yield for circularly-polarized pumps of same helicity, surprisingly, the emitted THz radiation is not linearly-polarized. This effect is explained by means of comprehensive 3D numerical simulations highlighting the role of the spatial alignment and non-collinear propagation of the two colors. [ABSTRACT FROM AUTHOR]