Laser Interaction Research Articles

Fabrication of Laser-Induced Graphene Based Flexible Sensors Using 355 nm Ultraviolet Laser and Their Application in Human-Computer Interaction System.

In recent years, flexible sensors based on laser-induced graphene (LIG) have played an important role in areas such as smart healthcare, smart skin, and wearable devices. This paper presents the fabrication of flexible sensors based on LIG technology and their applications in human-computer interaction (HCI) systems. Firstly, LIG with a sheet resistance as low as 4.5 Ω per square was generated through direct laser interaction with commercial polyimide (PI) film. The flexible sensors were then fabricated through a one-step method using the as-prepared LIG. The applications of the flexible sensors were demonstrated by an HCI system, which was fabricated through the integration of the flexible sensors and a flexible glove. The as-prepared HCI system could detect the bending motions of different fingers and translate them into the movements of the mouse on the computer screen. At the end of the paper, a demonstration of the HCI system is presented in which words were typed on a computer screen through the bending motion of the fingers. The newly designed LIG-based flexible HCI system can be used by persons with limited mobility to control a virtual keyboard or mouse pointer, thus enhancing their accessibility and independence in the digital realm.

Unraveling spatial variations of graphenization of Kapton polyimide via CO2 laser interaction: a comprehensive theoretical simulation and Raman spectroscopy mapping study

Unraveling spatial variations of graphenization of Kapton polyimide via CO2 laser interaction: a comprehensive theoretical simulation and Raman spectroscopy mapping study

Modeling of Short-Pulse Laser Interactions with Monolithic and Porous Silicon Targets with an Atomistic-Continuum Approach.

The acquisition of reliable knowledge about the mechanism of short laser pulse interactions with semiconductor materials is an important step for high-tech technologies towards the development of new electronic devices, the functionalization of material surfaces with predesigned optical properties, and the manufacturing of nanorobots (such as nanoparticles) for bio-medical applications. The laser-induced nanostructuring of semiconductors, however, is a complex phenomenon with several interplaying processes occurring on a wide spatial and temporal scale. In this work, we apply the atomistic-continuum approach for modeling the interaction of an fs-laser pulse with a semiconductor target, using monolithic crystalline silicon (c-Si) and porous silicon (Si). This model addresses the kinetics of non-equilibrium laser-induced phase transitions with atomic resolution via molecular dynamics, whereas the effect of the laser-generated free carriers (electron-hole pairs) is accounted for via the dynamics of their density and temperature. The combined model was applied to study the microscopic mechanism of phase transitions during the laser-induced melting and ablation of monolithic crystalline (c-Si) and porous Si targets in a vacuum. The melting thresholds for the monolithic and porous targets were found to be 0.32 J/cm2 and 0.29 J/cm2, respectively. The limited heat conduction mechanism and the absence of internal stress accumulation were found to be involved in the processes responsible for the lowering of the melting threshold in the porous target. The results of this modeling were validated by comparing the melting thresholds obtained in the simulations to the experimental values. A difference in the mechanisms of ablation of the c-Si and porous Si targets was considered. Based on the simulation results, a prediction regarding the mechanism of the laser-assisted production of Si nanoparticles with the desired properties is drawn.

Femtosecond multimodal imaging with a laser-driven X-ray source

Laser-plasma accelerators are compact linear accelerators based on the interaction of high-power lasers with plasma to form accelerating structures up to 1000 times smaller than standard radiofrequency cavities, and they come with an embedded X-ray source, namely betatron source, with unique properties: small source size and femtosecond pulse duration. A still unexplored possibility to exploit the betatron source comes from combining it with imaging methods able to encode multiple information like transmission and phase into a single-shot acquisition approach. In this work, we combine edge illumination-beam tracking (EI-BT) with a betatron X-ray source and present the demonstration of multimodal imaging (transmission, refraction, and scattering) with a compact light source down to the femtosecond timescale. The advantage of EI-BT is that it allows multimodal X-ray imaging technique, granting access to transmission, refraction and scattering signals from standard low-coherence laboratory X-ray sources in a single shot.

High field suppression of bremsstrahlung emission in high-intensity laser–plasma interactions

The interaction of high-intensity lasers with plasma is predicted to produce extreme quasi-static magnetic fields with magnitudes approaching Megatesla levels. In relativistically transparent plasmas, these fields can enhance direct laser acceleration and allow efficient gamma-ray emission by accelerated electrons. However, due to the so-called magnetic suppression effect, the magnetic field can also affect radiating electron trajectories and, thus, reduce the emission probability of the bremsstrahlung. This is the first study to examine the bremsstrahlung suppression mechanism in the context of high-intensity laser–plasma interactions. Our paper describes a new module that integrates the suppression effect into the standard bremsstrahlung module of the EPOCH particle-in-cell code by considering the impact of magnetic fields and extending the analysis to electric fields. We also investigate this suppressing mechanism's effect on the emitting electron's dynamics. Our findings show that this mechanism not only suppresses low-energy emissions but also has an impact on the dynamics of the radiating electrons.

Corrigendum to “A critical review on the simulation of ultra-short pulse laser interactions based on a two-temperature model (TTM)” [Opt. Laser Technol. 159 (2023) 109001

Corrigendum to “A critical review on the simulation of ultra-short pulse laser interactions based on a two-temperature model (TTM)” [Opt. Laser Technol. 159 (2023) 109001

Parametric instabilities and hot electron generation in the interactions of broadband lasers with inhomogeneous plasmas

The development of parametric instabilities in the interaction of a large-scale inhomogeneous plasma with either a monochromatic or a broadband laser pulse is investigated theoretically and numerically. For a monochromatic laser at an intensity of W cm−2, the development of Stimulated Brillouin Scattering (SBS) in the relatively low density region will obviously dissipate pump laser and hence inhibit the development of Two-Plasmon Decay (TPD) and absolute Stimulated Raman Scattering (SRS) near the quarter-critical density. By using a laser with a moderate fractional bandwidth (∼1.0%) at the same averged intensity, it is found that the laser reflectivity will be greatly reduced since the SBS can be suppressed effectively due to its low linear growth rate. On the contrary, the TPD and absolute SRS are obviously enhanced since the in situ laser intensity near the quarter-critical density becomes stronger in this case. As a result, the hot electron generation due to the TPD and absolute SRS is dramatically enhanced as well. This indicates that the competition between various parametric instabilities in a large-scale inhomogeneous plasma makes it more challenging to simultaneously suppress all kinds of parametric instabilities by using broadband lasers. Particular attention should be paid to the TPD, which not only has a relatively large linear growth rate but also is efficient in generating harmful hot electrons. Increasing the laser bandwidth further, the hot electron generation will be finally reduced as long as the TPD and SRS are also suppressed with a sufficient bandwidth (3%) at the intensity of W cm−2 that may be encountered in some novel ignition schemes such as shock ignition. However, it is worth noting that the laser bandwidth required to mitigate parametric instabilities and hot electron production strongly depends on laser intensity. A moderate laser bandwidth (∼1%) may be sufficient to mitigate both the laser reflectivity and hot electron production for typical ICF target designs operated with laser intensities lower than 1015 W cm−2.

Modification of Diamond Surface by Femtosecond Laser Pulses

The basic mechanisms of laser interaction with synthetic diamond are reviewed. The characteristics of the main regimes of diamond surface etching are considered. In addition to the well-known graphitization and ablation processes, nanoablation and accumulative graphitization, which have attracted relatively recent attention, are described in detail. The focus is on femtosecond (fs) laser exposure, which allows for the formation of a dense cold electron–hole plasma in the focal zone and minimal overheating in the surrounding area. This potentially opens the way to the development of unique laser-based technologies that combine physical and chemical processes for precise surface treatment and functionalization. The physical limitations that determine how precisely the diamond surface can be treated by short-pulsed laser radiation and possible ways to overcome them with the ultimate goal of removing ultrathin layers of the material are discussed. Special attention is paid to the novel possibility of inducing the local formation of point active defects—nitrogen vacancy (NV) complexes in the laser-irradiated zone. Such defects have been at the forefront of solid-state physics for the past thirty years due to continuous attempts to exploit their unique properties in quantum optics, quantum computing, magnetometry, probing, and other fields. Both regimes of NV center formation with and without graphitization of the diamond lattice are considered. Thus, it is shown that intense pulsed laser irradiation is a perfect tool for the processing of synthetic diamonds at the micro-, nano-, and even at the atomic level, which can be well controlled and managed.

Effect of the 1064 nm Nd: YAG Laser on the MICs of Antifungals Used in Clinical Practice for the Treatment of Fungal Nail Infections.

Introduction: The fungal nail infection (onychomycosis) involves 18%-40% of all nail disorders, which, although not fatal, can cause mechanical, aesthetic, occupational, and economic problems. Drug treatments due to prolonged treatment periods, drug interactions, adverse effects, and slow progression may associate with numerous negative outcomes. This study aimed to evaluate the long-pulsed 1064-nm Nd: YAG laser effect on fungal colonies and subsequently possible change in the minimum inhibitory concentrations (MICs) of common antifungals compared with the same non-lasered colonies as a novel way to investigate laser and antifungal interaction. Methods: Sixty onychomycosis samples consisting of saprophyte (n=20), dermatophyte (n=20), and yeast (n=20) duplicate colonies were isolated. A series was treated by a long-pulsed 1064-nm Nd: YAG laser. Afterward, the MIC (CLSI-M38-A2 and CLSI-M27-A3) of two series against common antifungals were compared. Results: After 1064-nm Nd: YAG laser irradiation in all 20 tested saprophytes, the MICs of terbinafine (P value<0.035) were changed, and in all 20 tested dermatophytes, the MICs of voriconazole (P value<0.021) were changed. Also, in all 20 tested yeasts, the MICs of caspofungin (P value<0.037) were changed. Moreover, in saprophytes, dermatophytes, and yeasts, significant changes in the MICs of itraconazole (P value<0.032), terbinafine (P value<0.025), and caspofungin (P value<0.037) were detected. Our result showed the GM MICs of the 1064-nm Nd: YAG laser in all saprophyte, dermatophyte, and yeast groups were lower than in the control group. Conclusion: The present study indicated that the long-pulsed 1064-nm Nd: YAG laser significantly changes the MICs of antifungals in onychomycosis clinical samples.

Molecular Dynamics Modeling of Pulsed Laser Fragmentation of Solid and Porous Si Nanoparticles in Liquid Media.

The production of non-toxic and homogeneous colloidal solutions of nanoparticles (NPs) for biomedical applications is of extreme importance nowadays. Among the various methods for generation of NPs, pulsed laser ablation in liquids (PLAL) has proven itself as a powerful and efficient tool in biomedical fields, allowing chemically pure silicon nanoparticles to be obtained. For example, laser-synthesized silicon nanoparticles (Si NPs) are widely used as contrast agents for bio visualization, as effective sensitizers of radiofrequency hyperthermia for cancer theranostics, in photodynamic therapy, as carriers of therapeutic radionuclides in nuclear nanomedicine, etc. Due to a number of complex and interrelated processes involved in the laser ablation phenomenon, however, the final characteristics of the resulting particles are difficult to control, and the obtained colloidal solutions frequently have broad and multimodal size distribution. Therefore, the subsequent fragmentation of the obtained NPs in the colloidal solutions due to pulsed laser irradiation can be utilized. The resulting NPs' characteristics, however, depend on the parameters of laser irradiation as well as on the irradiated material and surrounding media properties. Thus, reliable knowledge of the mechanism of NP fragmentation is necessary for generation of a colloidal solution with NPs of predesigned properties. To investigate the mechanism of a laser-assisted NP fragmentation process, in this work, we perform a large-scale molecular dynamics (MD) modeling of FS laser interaction with colloidal solution of Si NPs. The obtained NPs are then characterized by their shape and morphological properties. The corresponding conclusion about the relative input of the properties of different laser-induced processes and materials to the mechanism of NP generation is drawn.

Physics-Informed Neural Networks for the Heat Equation with Source Term under Various Boundary Conditions

Modeling of physical processes as partial differential equations (PDEs) is often carried out with computationally expensive numerical solvers. A common, and important, process to model is that of laser interaction with biological tissues. Physics-informed neural networks (PINNs) have been used to model many physical processes, though none have demonstrated an approximation involving a source term in a PDE, which modeling laser-tissue interactions requires. In this work, a numerical solver for simulating tissue interactions with lasers was surrogated using PINNs while testing various boundary conditions, one with a radiative source term involved. Models were tested using differing activation function combinations in their architectures for comparison. The best combinations of activation functions were different for cases with and without a source term, and R2 scores and average relative errors for the predictions of the best PINN models indicate that it is an accurate surrogate model for corresponding solvers. PINNs appear to be valid replacements for numerical solvers for one-dimensional tissue interactions with electromagnetic radiation.

A simulation study of electron-scale turbulence generation by nonlinear wave–wave interaction in laser-produced plasmas

A laboratory simulation of a model based on the nonlinear interaction of plasma waves is presented to study the electron-scale magnetic turbulence in the magnetized plasma. In this perspective, the model equations of the Trivelpiece–Gould (TG) mode and extraordinary mode (pump wave) are developed, taking the relativistic change in electron mass and the ponderomotive force into account. Laboratory simulations utilizing the pseudo-spectral method along with the predictor–corrector scheme and finite difference method are performed to solve the formulated coupled model equations. The propagation angle (θ) of the TG mode from the magnetic field affects the dispersive properties of the dynamics (TG mode), which, in turn, impact the density perturbation, scale size of the filamentary structures, density harmonics, magnetic field enhancement, and the spectral index of the turbulence generation. The simulation results reveal that the observed turbulent spectra resemble the magnetic turbulence reported in various studies of the interaction of the intense laser with plasma at the laboratory astrophysics scale relevant to astrophysical events. A simplified model in the paraxial limit is also given to understand the effect of the propagation direction (angle of propagation θ) of the TG mode on the localized structures of the pump laser beam in the magnetized plasma.

Optical Properties of Nanoparticles Dispersed in Ambient Medium and their Dependences on Temperature

Abstract: This review describes the basic and application aspects of the optical properties of nanoparticles (NPs), which determine the dynamics and results of optical (laser) radiation interaction with NPs and their surroundings through NP light absorption and heat generation. In addition to the importance of primary optical processes, the thermal application of the light–NP interaction has attracted significant interest from various areas ranging from photochemistry to laser material processing and nanobiomedicine. First of all, the information provided is intended for laser specialists, photochemists and nanobiologists who are not so familiar with various optical data for understanding of the influence of NP optical properties on the results of optical or laser action on NPs and medium. Secondly, our review will be useful for researchers who conduct high-temperature investigations of the intense optical action on NPs that needs to take into account the dependence of NP optical properties on its temperature under NP heating. Our attention is focused on two variants of the applications of NP optical properties. Firstly, we shortly reviewed the optical properties of NPs at their initial or slightly higher temperatures reached under the influence of moderate radiation intensity. They are presented in numerous publications and are used as basic data. On the other side, the development of modern high-temperature laser and optical technologies needs to use the NPs optical properties at temperatures of about 1x103 K and more. For high power laser and optical technologies, it is necessary to take into account the temperature dependences of the optical parameters of various metals, dielectrics and other materials. Among these technologies, one should list laser processing of NPs, thermal laser biomedicine, solar and photo nanocatalysis, solar nanostructured absorbers. The selection and use of suitable optical properties of NPs are crucial to successful achievements and results in high-temperature experiments and applications. Novel information on optical property dependence on temperature obtained from currently available literature has been presented for possible applications in optical and laser high-temperature processes interactions with NPs. However, unfortunately, the essential information on the effect of temperature on the optical properties of NPs is currently limited. In addition to the latest information, this review also includes the figures obtained by our own calculations to provide readers with a better understanding of the NP optical properties. From the side of the application, the use of NP optical properties is considered, which provide multiple varieties of moderate and high-temperature technology opportunities, many of which are ongoing and some of them are promising bright results in the near future. The beneficial outcome and the results of further activities in the research of intense laser and optical interactions with NPs can influence various fields of science and technology: nano and photochemistry, biomedicine, nanophysics, material science, etc.

Formation and modulation of multi-pulse femtosecond laser-induced periodic surface structures by electromagnetic and partial differential equation simulations.

In order to demonstrate the formation of laser-induced periodic surface structures (LIPSS), simulations were performed to investigate the effect of multiple femtosecond laser pulses with different laser energy densities on a Ti6Al4V surface. In this work, a set of partial differential equations calculating the electron and lattice temperature variations, followed by coupling with an electric field, is used to analyze the evolution of the periodic surface structure induced by the interaction of the femtosecond laser with the material. As the number of pulses increases, the surface structure of the material changes from none to produce LIPSS structure and from low spatial frequency LIPSS (LSFL) structure to high spatial frequency LIPSS (HSFL) structure. In order to compare the results, single-point laser scanning ablation experiments were carried out at femtosecond laser energy. The experimental results are consistent with the simulation results.

Transient electron temperature and density changes in water breakdown induced by femtosecond laser pulses

When a femtosecond laser pulse travels through water, optical breakdown occurs when the laser intensity exceeds a certain threshold. This photoionization (PI) process and the resulting laser-induced plasma can strongly influence the laser ablation of substances, including transparent biological tissue, etc. However, numerical models of the initial evolution of the laser plasma and its early electron temperature remain inadequate. Here, a transient ionization rate equation involving the solvation process is proposed for calculating the free-electron number density (FED) generated during the interaction of the femtosecond laser with the water surface, along with the temporal evolution of the electron temperature in the focusing region during the entire femtosecond laser pulse utilizing an improved temperature model. The predictions of the proposed model are in better agreement with the experimentally determined breakdown thresholds. The results indicate that the existence of solvated electrons has a considerable influence on the determination of the optical breakdown threshold in water, which may also be one of the reasons why traditional numerical models consistently fail to forecast the actual breakdown threshold.

Self-generated magnetic collimation mechanism driven by ultra-intense LG laser

Collimation control of energetic plasma beams is crucial in the laser–plasma field. In this paper, we report on a self-collimated acceleration scheme for a plasma beam using an ultra-intense Laguerre–Gaussian (LG) laser irradiating a solid target. Three-dimensional (3D) particle-in-cell simulations show that a plasma beam with a high current density is stably formed by the radiation pressure of the hollow LG laser. The initial interaction of LG laser with solid target can be approximately researched by a deformable mirror model. Under the effect of the ponderomotive force of the LG laser, the plasma converges in the center axis to form a narrow beam. An elongated strong-magnetic tunnel (B ∼ 2 kT) is self-generated around the plasma beam, capable of trapping some electrons in a region with a radius of less than 500 nm (r &amp;lt; 500 nm). Compared with the case driven by the conventional Gaussian laser, the beam radius size is dramatically reduced from the microscale to hundreds on the nanoscale. The beam density is increased by at least ten times. Such an interesting scheme can provide a feasible and efficient way to achieve and enhance the collimation of energetic particle beams, which may benefit the general applications of fast ignition in inertial fusion, radiotherapy, realization of high-energy density states, and so on.

Study of propagation of skew cosh Gaussian laser beam in attenuated magneto plasma

Self-focusing of a laser beam is one of the major consequences of nonlinear interaction of laser with plasma. In this paper, self-focusing of skew cosh Gaussian (skew-ChG) laser beam is studied in anisotropic, collisional plasma where in externally exponentially decreasing magnetic field is applied. Skewness parameters in the field profile of skew-ChG laser beam eventually determine intensity profile of the beam. The symmetry in skewness parameter in two transverse directions simplifies the calculations considerably. Second order, nonlinear, ordinary, coupled differential equations for Beam Width Parameters (BWP) are obtained using Akhmanovs approach under Wentzel–Kramers–Brillouin (WKB) and paraxial approximations which are solved numerically. For given amplitude of applied magnetic field, attenuated oscillatory self-focusing is observed with respect to change in attenuation coefficient.

Time evolution of temporal, spatial and spectral distribution of high-energy electron radiation in intense laser pulses

To study the time evolution of high-energy electron radiation in circularly polarized intense laser pulses in detail, a model of the interaction between the high-energy single electron and intense laser pulses is constructed based on the Lagrangian equation and the electron energy equation. Through simulation, this article vividly displays the evolution process of radiation in the spatial, frequency and time domain. By modulating the interaction time between the laser and electron and referring to the spatial distribution image of energy, the value and direction of the maximum radiation energy per unit solid angle are calculated. In addition, in specific directions, this paper discusses the effects of interaction duration on the energy frequency distribution and the power variation pattern. The results prove that the maximum radiation energy per unit solid angle will appear when the interaction time comes to about 450 fs, which is also the boundary moment when the frequency and time spectrum no longer change obviously. Therefore, by modifying the duration of the electron–laser interaction, it is possible to produce the electron radiation with desired characteristics more precisely.

Analysis of frequency chirping on the electron bunch acceleration during Laguerre–Gauss laser interaction

We intend to examine the impact of frequency chirping on the efficient vacuum acceleration of an electron bunch using a chirped Laguerre–Gauss (LG) laser pulse. The study demonstrates that achieving high-energy electron acceleration relies not only on significant pulse asymmetry but also on ensuring phase synchronization in the LG laser interaction. The findings highlight the feasibility of generating outgoing electron bunches with high energy and low divergence through the selection of an optimal chirping value. Furthermore, we establish that chirping the LG laser pulse facilitates the acceleration of electrons to high energy using a lower laser intensity compared to the scenario without chirping.

Dynamics of femtosecond heated warm dense copper with time-resolved L3-edge XANES.

Combining experimental set up and ab initio molecular dynamics simulations, we were able to follow the time evolution of the X-ray absorption near edge spectrum (XANES) of a dense copper plasma. This provides a deep insight into femtosecond laser interaction with a metallic copper target. This paper presents a review of the experimental developments we made to reduce the X-ray probe duration, from approximately 10 ps to fs duration with table-top laser systems. Moreover, we present microscopic scale simulations, performed with Density Functional Theory, as well as macroscopic simulations considering the Two-Temperature Model. These tools allow us to get a complete picture of the evolution of the target at a microscopic level, from the heating process to the melting and expansion stages, with a clear view of the physics involved during these processes. This article is part of the theme issue 'Dynamic and transient processes in warm dense matter'.