Ultrashort Laser Pulses Research Articles

Quantum electrodynamics study of polarization effects on the properties of high harmonics of an intense ultrashort laser pulse interacting with relativistic electrons

Quantum electrodynamics study of polarization effects on the properties of high harmonics of an intense ultrashort laser pulse interacting with relativistic electrons

Femtosecond Laser Ablation and Delamination of Functional Magnetic Multilayers at the Nanoscale.

Laser nanostructuring of thin films with ultrashort laser pulses is widely used for nanofabrication across various fields. A crucial parameter for optimizing and understanding the processes underlying laser processing is the absorbed laser fluence, which is essential for all damage phenomena such as melting, ablation, spallation, and delamination. While threshold fluences have been extensively studied for single compound thin films, advancements in ultrafast acoustics, magneto-acoustics, and acousto-magneto-plasmonics necessitate understanding the laser nanofabrication processes for functional multilayer films. In this work, we investigated the thickness dependence of ablation and delamination thresholds in Ni/Au bilayers by varying the thickness of the Ni layer. The results were compared with experimental data on Ni thin films. Additionally, we performed femtosecond time-resolved pump-probe measurements of transient reflectivity in Ni to determine the heat penetration depth and evaluate the melting threshold. Delamination thresholds for Ni films were found to exceed the surface melting threshold suggesting the thermal mechanism in a liquid phase. Damage thresholds for Ni/Au bilayers were found to be significantly lower than those for Ni and fingerprint the non-thermal mechanism without Ni melting, which we attribute to the much weaker mechanical adhesion at the Au/glass interface. This finding suggests the potential of femtosecond laser delamination for nondestructive, energy-efficient nanostructuring, enabling the creation of high-quality acoustic resonators and other functional nanostructures for applications in nanosciences.

Ablation characteristics of tungsten with ultra-short laser pulses

Ablation characteristics of tungsten with ultra-short laser pulses

Power dependent tunable optical nonlinearity in Iron oxide/Borophene core-shell nanoparticles under ultrashort laser excitation

Two-dimensional (2D) nanomaterials find immense applications in ultrafast photonics and optical switching systems due to their fascinating nonlinear optical (NLO) characteristics. This work presents a systematic investigation of laser power-dependent nonlinear optical characteristics of borophene nanosheets in a core-shell nanostructure. For this purpose, we have synthesized Borophene encapsulated Iron oxide (Fe3O4) core-shell nanoparticles (Fe3O4/Borophene CSNPs). The CSNPs were synthesized by mixing and annealing sodium borohydride (NaBH4) as a boron precursor with iron oxide nanoparticles (Fe3O4 NPs) in a controlled environment using chemical vapor deposition technique (CVD) followed by characterization using XRD, FTIR Spectroscopy, UV–vis absorption spectroscopy, TEM, SEM, and EDX techniques. Magnetic properties were analyzed by a vibrating sample magnetometer (VSM) which shows that the saturation magnetization of Fe3O4 NPs increases after being encapsulated in borophene nanosheets. The role of borophene in modifying the NLO characteristics of Fe3O4/Borophene CSNPs was studied using a power-dependent Z-scan technique utilizing ultrashort (femtosecond) laser pulses at a wavelength of 800 nm in both open and close aperture configuration. It was found that borophene-coated Fe3O4 NPs reveal tunable NLO properties that resemble the NLO characteristics of borophene nanosheets with enhanced features. This provides insights into an interaction between materials in NLO phenomena and illustrates the distinctive performance of the core-shell nanostructure. The tunable NLO properties of Fe3O4/Borophene CSNPs offer an innovative approach for developing optoelectronics and ultrafast nonlinear photonic devices.

Optical manipulation of ultrashort laser pulses for applications in challenging environments

Over the last few years, high throughput ultrashort-pulse laser sources have become increasingly affordable. This facilitated the emergence of many applications that require sub-micron precision material modification. Processes have been demonstrated in applications including micro-structuring semiconductor chips, manufacturing complex 3D parts or inscribing optical materials for data storage. Furthermore, recent progress in techniques for the optical manipulation of ultrashort laser pulses opened up new avenues in applications for challenging environments such as those involving high energy physics or particle beam radiotherapy. These applications require high-resolution 3D structures to be produced in radiation tolerant materials, to make particle sensors with the required sensitivity and resolution. For such processes, accurate spatial and temporal structuring and manipulating of optical parameters such as polarization, wavefront and intensity of laser beams, is essential. This paper presents recent results in advanced optical manipulation including the induction of helical or longitudinal fields at the focus. The resulting laser material coupling interactions are characterized and their suitability for making particle sensors from radiation hard materials considered.

Bayesian optimization of proton generation in terawatt laser–CH2 cluster interactions within a plasma channel

Improving the energy efficiency in generating high-energy proton or boron ions is crucial for advancing the feasibility of neutronless laser-based proton–boron (p-B11) fusion reactions. The primary objective of this work is to optimize the fusion energy efficiency of a proposed advanced p-B11 fusion scheme. In the proposed scheme, an ultrashort laser pulse is guided by a plasma channel filled with carbon–hydrogen (CH2) clusters. The MeV protons are generated by the Coulomb explosion (CE) of the cluster, which, therefore, interact with surrounding boron to produce alpha particles. To evaluate the fusion energy efficiency under various conditions, 2D particle-in-cell (PIC) simulations are used, supplemented with analytical calculations and estimations. The Bayesian optimization (BO) algorithm is utilized to optimize the key interaction parameters. The BO approach allows us to identify optimal cluster and laser parameters that would have higher fusion energy efficiency.

ULPING-Based Titanium Oxide as a New Cathode Material for Zn-Ion Batteries

The need for alternative energy storage options beyond lithium-ion batteries is critical due to their high costs, resource scarcity, and environmental concerns. Zinc-ion batteries offer a promising solution, given zinc’s abundance, cost effectiveness, and safety, particularly its compatibility with non-flammable aqueous electrolytes. In this study, the potential of laser-ablation-based titanium oxide as a novel cathode material for zinc-ion batteries was investigated. The ultra-short laser pulses for in situ nanostructure generation (ULPING) technique was employed to generate nanostructured titanium oxide. This laser ablation process produced highly porous nanostructures, enhancing the electrochemical performance of the electrodes. Zinc and titanium oxide samples were evaluated using two-electrode and three-electrode setups, with cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and galvanostatic charge–discharge (GCD) techniques. Optimal cathode materials were identified in the Ti-5W (laser ablated twice) and Ti-10W (laser ablated ten times) samples, which demonstrated excellent charge capacity and energy density. The Ti-10W sample exhibited superior long-term performance due to its highly porous nanostructures, improving ion diffusion and electron transport. The potential of laser-ablated titanium oxide as a high-performance cathode material for zinc-ion batteries was highlighted, emphasizing the importance of further research to optimize laser parameters and enhance the stability and scalability of these electrodes.

Growth, structure and spectroscopic properties investigation on a novel Tm3+-doped disordered Ca(GdxY1-x)Al3O7 hybrid melilite crystal

A disordered Tm3+-doped Ca(GdxY1-x)Al3O7 hybrid melilite crystal (Tm:CGYAM) was successfully grown by using the optical floating zone method, and its structure and spectroscopic properties were studied thoroughly. Structure analysis shows that the Tm:CGYAM crystallizes in tetragonal system. The maximum phonon energy of Tm:CGYAM crystal is estimated to be 765.8 cm−1. Absorption spectrum shows that the absorption cross-section of the Tm:CGYAM crystal is 0.44 ×10−20 cm2 at 788.5 nm, with a FWHM of 34.5 nm. The radiative lifetime of Tm3+:3F4→3H6 transition in Tm:CGYAM crystal is calculated to be 5.35 ms by J-O analysis. The emission cross-sections are 0.321×10−20 cm2 at 1785 nm and 0.324×10−20 cm2 at 1945 nm. The FWHM of Tm3+:3F4→3H6 transition emission band reaches 280 nm. By fitting the fluorescence decay curve, the fluorescence lifetime of Tm3+:3F4 level is estimated as 4.55 ms. The gain cross-section of Tm:CGYAM crystal achieves positive in the range of 1771–2200 nm once the population inversion level reaches 10 %. All the experimental results support the Tm:CGYAM crystal can be a promising candidate material for solid state tunable or ultrashort pulse laser application.

Targeted Microforming of Borosilicate Glass Induced by a Laser‐Ablation‐Free Process Using Femtosecond Pulses

AbstractThe use of ultrashort pulse lasers opens up a wide range of possibilities for processing dielectric materials. The present study focuses on the investigation of the ablation‐free microscopic surface modification of borosilicate glass using femtosecond laser radiation (350 fs at 515 nm wavelength) in a scanning machining process. Furthermore, its aim is to analyze the relationship between the laser process parameters and the microscopic changes in the surface topography observed. The characteristic of the generated surface structure, which takes place below the ablation threshold, shows both elevations and depressions within the irradiated field (2 × 2 mm2). The realized structures reach a profile height Peak‐to‐Valley (PV) of up to 10 µm. The amount of surface deformation depends on the selected parameters such as laser fluence, number of passes, and scanning strategy. The microdeformation is detected on both the top and bottom sides of the processed glass material with a thickness ≤1 mm. The influence of the temporal and spatial energy distribution on the material modification is discussed, demonstrating the possibilities of microforming of silicate glasses using ultrashort pulsed laser radiation.

Acousto-optic femtosecond laser beam shaping for bottle-beam generation

Abstract This study explores the properties of a laser beam shaping system comprising an acousto-optic dispersive delay line (AODDL) and an acousto-optic tunable filter (AOTF) for ultrashort laser pulse shaping. The system demonstrates the AODDL’s ability to generate signals with arbitrarily positioned transmission windows and investigates the impact of spectral width on field distributions. The AOTF’s frequency scanning and simultaneous control of two and three spectral components are presented. The experimental setup utilizes femtosecond laser radiation, and the results highlight the system’s versatility for programmable spectral and spatial filtering, offering potential applications in advanced optical manipulation.

A six degrees of freedom femtosecond laser system for fabrication of small-scale mechanical property specimens.

We present the details of a novel ultra-short pulsed laser machining workstation that has been employed for high-throughput laser machining of small-scale mechanical property specimens. This system employs a six degrees of freedom hexapod positioning stage capable of macroscopic movements at high positional accuracy. We developed a methodology that uses quantitative image analysis to measure key parameters required to minimize the hexapod positioning and rotational error. Application of this system to laser machining of small-scale 316L stainless steel tensile specimens and ultra-high molecular weight polyethylene compressive specimens using eucentric tilt and rotation about the specimen axis will be shown, where serial laser milling at a specimen tilt angle of 10° was used to effectively eliminate any taper in the sample cross section that is typically found in laser machining.

Cleaning of laser-induced periodic surface structures on copper by gentle wet chemical processing

Laser-induced periodic surface structures (LIPSS) attract considerable attention due to the manifold applications enabled by these self-organised structures ranging from optical colouring to bio-mimicking or wetting effects. The mechanism of LIPSS-formation at metal surfaces includes laser-ablation processes that results in phase transitions, explosive material removal and partial redeposition of the ablation products in the form of nanoscopic debris or even sub-micrometre-sized spherical particles in case of melt ejection. For some applications, these particulates, debris, and microscopic features on top of the periodic surface structures are disadvantageous. We studied wet-chemical cleaning approaches to remove redeposited material from LIPSS to enhance their applicability. LIPSS on copper with a lateral periodicity of ∼ 365 nm, that were fabricated by ultrashort pulse laser exposure(λ: 515 nm, tp: 260 fs), were cleaned with different liquids ranging from solvents to microemulsions. The surface morphologies were characterised by scanning electron microscopy (SEM), atomic force microscopy (AFM) and transmission electron microscopy(TEM) to study the surface topography, the size and density of surface particulates as well as other surface contaminations before and after wet cleaning. The LIPSS surface composition was analysed by X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and Energy-dispersive x-ray spectroscopy (EDX) at the FIB-cross sections. The different cleaning approaches are classified with respect to their capability to remove particles and contaminations as well as to their influence on the morphology and shape of LIPSS pattern, whereby substantial differences are found. At least two wet-chemical solutions enable the removal of nanoparticles with only minor modification of the LIPSS topography. The main effect of wet cleaning is the detachment of particulates including sub-micrometre-sized spheres due to a gentle and selective etching of the interface region between the LIPSS and the redeposited material that comprise of modified copper and copper oxides.

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).

Modeling of Ultrafast Phenomena Induced by Ultrashort Pulsed Lasers

Modeling of Ultrafast Phenomena Induced by Ultrashort Pulsed Lasers

Giant ultrafast dichroism and birefringence with active nonlocal metasurfaces

Switching of light polarization on the sub-picosecond timescale is a crucial functionality for applications in a variety of contexts, including telecommunications, biology and chemistry. The ability to control polarization at ultrafast speed would pave the way for the development of unprecedented free-space optical links and of novel techniques for probing dynamical processes in complex systems, as chiral molecules. Such high switching speeds can only be reached with an all-optical paradigm, i.e., engineering active platforms capable of controlling light polarization via ultrashort laser pulses. Here we demonstrate giant modulation of dichroism and birefringence in an all-dielectric metasurface, achieved at low fluences of the optical control beam. This performance, which leverages the many degrees of freedom offered by all-dielectric active metasurfaces, is obtained by combining a high-quality factor nonlocal resonance with the giant third-order optical nonlinearity dictated by photogenerated hot carriers at the semiconductor band edge.

Supercontinua from integrated gallium nitride waveguides

Supercontinua are broadband spectra that are essential to optical spectroscopy, sensing, imaging, and metrology. They are generated from ultrashort laser pulses through nonlinear frequency conversion in fibers, bulk media, and chip-integrated waveguides. For any generating platform, balancing the competing criteria of strong nonlinearity, transparency, and absence of multiphoton absorption is a key challenge. Here, we explore supercontinuum generation in integrated gallium nitride (GaN) waveguides, which combine a high Kerr nonlinearity, mid-infrared transparency, and a large bandgap that prevents two- and three-photon absorption in the technologically important telecom C-band, where compact erbium-based pump lasers exist. Using this type of laser, we demonstrate tunable dispersive waves and gap-free spectra extending to almost 4 µm in wavelength, which is relevant to functional group chemical sensing. Additionally, leveraging the material’s second-order nonlinearity, we implement on-chip f-to-2f interferometry to detect the pump laser’s carrier-envelope offset frequency, which enables precision metrology. These results demonstrate the versatility of GaN-on-sapphire as a platform for broadband nonlinear photonics.

Strong-Field Ionization Phenomena Revealed by Quantum Trajectories.

We investigate the photoionization dynamics of atoms subjected to intense, ultrashort laser pulses through the use of quantum trajectories. This method provides a unique and consistent framework for examining electron dynamics within a time-dependent potential barrier. Our findings demonstrate that quantum trajectories offer additional insights into several key aspects of strong-field ionization, including the transition between ionization regimes, nonadiabatic effects under the barrier, the impact of the shape of the electronic potential, and the efficiency of over-the-barrier ionization.

Lens Fragmentation with Picosecond Laser Pulses After Artificial Cataract Induction with Microwaves.

Objectives: In this work we demonstrate the first laboratory study results of lens fragmentation with low-energy picosecond ultrashort laser pulses after artificial induction of cataract with microwave radiation on an ex vivo animal model. Background: This method will be evaluated with regard to the further development of lens fragmentation with novel ultrashort picosecond laser systems instead of ultrasonic phacoemulsification or the significantly more complex femtosecond laser fragmentation. Methods: As samples we used postmortem porcine eyes. The lenses were dissected and then irradiated in a microwave oven for artificial cataract induction. Subsequent computer-driven lens fragmentation was performed with a 12 ps, 1064 nm pulsed laser source with 100 µJ pulse energy, and 10 kHz pulse repetition rate. Results: Both the artificial cataract induction and the lens fragmentation were demonstrated. When inducing cataract, different degrees/stages of opaqueness and hardness could be achieved with different irradiation times and methods. The fragmentation with 12 ps pulses led to good results with regard to ablation depth and rate, especially for the softer lenses. Conclusions: As could be shown, low-energy picosecond ultrashort laser pulses are feasible for cataractous lens fragmentation on an ex vivo animal model with artificial cataract induction. Thus, this technique may influence future cataract surgeries by possibly being an alternative or extension to state-of-the-art methods. This will be evaluated with further tests and studies.

Ultrafast spallation dynamics of a thin gold film characterized by imaging pump-probe interferometry

Interferometry allows to measure microscopic displacements in the nanometer scale. This work introduces an imaging pump-probe interferometer that enables to detect the spatially resolved phase shift of the probe radiation being reflected on a sample surface after ultrashort pulsed laser excitation with a temporal resolution of 40 fs and a maximum temporal delay of 3 ns. The capability of the pump-probe interferometer is demonstrated on the spallation of a thin gold film upon femtosecond laser irradiation. The pump-probe interferometer enables to measure a minimum phase change of Δφ<π/10\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\Delta \\varphi <\\pi /10$$\\end{document} which corresponds to a displacement of Δh<\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\Delta h<$$\\end{document} 12.5 nm for the applied probe wavelength of 500 nm. Upon irradiation, two distinct phase changes are observable: First, an abrupt minor phase shift has been measured in the femtosecond range, which is attributed to the changed optical properties of the sample surface after excitation. Second, a more pronounced continuing phase shift increase is detectable after a few tens of picoseconds resulting from the onset of spallation. Based on the measured spatially resolved phase shift, the transient surface topography during the spallation is reconstructed. The determined velocity of the ablated material reaches a maximum of a few 1000 m/s at ten picosecond after irradiation and decreases to 250 m/s afterwards. Consequently, the introduced imaging pump-probe interferometer provides important insights into the physical processes during laser excitation as well as the subsequent laser-induced ablation, and will enable to validate theoretical models quantitatively in following studies.

Nucleation-assisted microthermometry: A novel application to fluid inclusions in halite

Halite deposits have long been utilized for interrogating past climate conditions. Microthermometry on halite fluid inclusions has been used to determine ancient water temperatures. One notable obstacle in performing microthermometric measurements, however, is the lack of a vapor bubble in the single-phase liquid inclusions at room temperature. (Pseudo-) isochoric cooling of the inclusions to high negative pressures, far below the homogenization temperature, has commonly been needed to provoke spontaneous vapor bubble nucleation in the liquid. High internal tensile stress in soft host minerals like halite, however, may induce plastic deformation of the inclusion walls, resulting in a wide scatter of measured homogenization temperatures. Nucleation-assisted (NA) microthermometry, in contrast, employs single ultra-short laser pulses provided by a femtosecond laser to stimulate vapor bubble nucleation in metastable liquid inclusions slightly below the expected homogenization temperature. This technique allows for repeated vapor bubble nucleation in selected fluid inclusions without affecting the volumetric properties of the inclusions, and yields highly precise and accurate homogenization temperatures.In this study, we apply, for the first time, NA microthermometry to fluid inclusions in halite and we evaluate the precision and accuracy of this thermometer utilizing (i) synthetic halite crystals precipitated under controlled laboratory conditions, (ii) modern natural halite that precipitated in the 1980s in the Dead Sea, and (iii) Late Pleistocene halite samples from a sediment core from Death Valley, CA. Our results demonstrate an unprecedented accuracy and precision of the method that provides a new opportunity to reconstruct reliable quantitative temperature records from evaporite archives.