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The ultrafast laser-matter interaction is explored to induce new pioneering principles and technologies into the realms of fundamental science and industrial production. The local thermal melting and connection properties of the ultrafast laser welding technology offer a novel method for welding of diverse transparent materials, thus having wide range of potential applications in aerospace, opto-mechanical systems, sensors, microfluidic, optics, etc. In this comprehensive review, tuning the transient electron activation processes, high-rate laser energy deposition, and dynamic evolution of plasma morphology by the temporal/spatial shaping methods have been demonstrated to facilitate the transition from conventional homogeneous transparent material welding to the more intricate realm of transparent/metal heterogeneous material welding. The welding strength and stability are also improvable through the implementation of real-time, in-situ monitoring techniques and the prompt diagnosis of welding defects. The principles of ultrafast laser welding, bottleneck problems in the welding, novel welding methods, advances in welding performance, in-situ monitoring and diagnosis, and various applications are reviewed. Finally, we offer a forward-looking perspective on the fundamental challenges within the field of ultrafast laser welding and identify key areas for future research, underscoring the imperative need for ongoing innovation and exploration. Recent advances in ultrafast laser welding of transparent materials are reviewed. The mechanism and characteristics of ultrafast laser welding are systematically revealed. The challenges encountered in welding applications are clarified. Ultrafast laser temporal-spatial shaping and on-line monitoring techniques are analyzed.

Ultrafast laser processing technology has offered a wide range of opportunities in micro/nano fabrication and other fields such as nanotechnology, biotechnology, energy science, and photonics due to its controllable processing precision, diverse processing capabilities, and broad material adaptability. The processing abilities and applications of the ultrafast laser still need more exploration. In the field of material processing, controlling the atomic scale structure in nanomaterials is challenging. Complex effects exist in ultrafast laser surface/interface processing, making it difficult to modulate the nanostructure and properties of the surface/interface as required. In the ultrafast laser fabrication of micro functional devices, the processing ability needs to be improved. Here, we review the research progress of ultrafast laser micro/nano fabrication in the areas of material processing, surface/interface controlling, and micro functional devices fabrication. Several useful ultrafast laser processing methods and applications in these areas are introduced. With various processing effects and abilities, the ultrafast laser processing technology has demonstrated application values in multiple fields from science to industry.

Laser processing implies the generation of a material function defined by the shape and the size of the induced structures, being a collective effect of topography, morphology, and structural arrangement. A fundamental dimensional limit in laser processing is set by optical diffraction. Many material functions are yet defined at the micron scale, and laser microprocessing has become a mainstream development trend. Consequently, laser microscale applications have evolved significantly and developed into an industrial grade technology. New opportunities will nevertheless emerge from accessing the nanoscale. Advances in ultrafast laser processing technologies can enable unprecedented resolutions and processed feature sizes, with the prospect to bypass optical and thermal limits. We will review here the mechanisms of laser processing on extreme scales and the optical and material concepts allowing us to confine the energy beyond the optical limits. We will discuss direct focusing approaches, where the use of nonlinear and near-field effects has demonstrated strong capabilities for light confinement. We will argue that the control of material hydrodynamic response is the key to achieve ultimate resolution in laser processing. A specific structuring process couples both optical and material effects, the process of self-organization. We will discuss the newest results in surface and volume self-organization, indicating the dynamic interplay between light and matter evolution. Micron-sized and nanosized features can be combined into novel architectures and arrangements. We equally underline a new dimensional domain in processing accessible now using laser radiation, the sub-100-nm feature size. Potential application fields will be indicated as the structuring sizes approach the effective mean free path of transport phenomena.

Ultrafast Bessel beams demonstrate a significant capacity of structuring transparent materials with a high degree of accuracy and exceptional aspect ratio. The ability to localize energy on the nanometer scale (bypassing the 100-nm milestone) makes them ideal tools for advanced laser nanoscale processing on surfaces and in the bulk. This allows to generate and combine micron and nano-sized features into hybrid structures that show novel functionalities. Their high aspect ratio and the accurate location can equally drive an efficient material modification and processing strategy on large dimensions. We review, here, the main concepts of generating and using Bessel non-diffractive beams and their remarkable features, discuss general characteristics of their interaction with matter in ablation and material modification regimes, and advocate their use for obtaining hybrid micro and nanoscale structures in two and three dimensions (2D and 3D) performing complex functions. High-throughput applications are indicated. The example list ranges from surface nanostructuring and laser cutting to ultrafast laser welding and the fabrication of 3D photonic systems embedded in the volume.

The aluminum alloy–fused silica joints have found extensive applications in various industrial contexts, with ultrafast laser technology as a precise and non-contact method for achieving such joints. However, low pulse energy (~ µJ) and limited element diffusion (~ µm) often lead to unsatisfactory bonding strength and strict surface requirements. This study used a 35 fs-mJ pulsed laser to weld fused silica and aluminum alloy without special surface preparations. The resulting weld region exhibited a complex aluminum-fused silica mixture with lengths of approximately 75 µm. Shrinkage cavities and microcracks were observed within the fused silica, and keyhole-shaped shrinkage cavities appeared on both sides of the weld center. Cross-bedded layers with micropores were also found in the aluminum substrate. EDS analyses revealed an unconventional redistribution of O elements that escaped from SiO2 in the weld region, and the bonding mechanism was identified as a fused silica-aluminum reciprocal mixture. The achieved maximum shear strength of 7.77 MPa was significantly higher than that of µJ-level pulsed laser welding, and fractures occurred at the solidification-native fused silica boundaries. This study suggests that mJ-level pulsed femtosecond laser transmission welding can enhance joint strength, eliminate the need for special surface preparations, and potentially overcome the challenge of aluminum-fused silica welding with a large interface gap.

Surface functionalization of metallic micro-nanoscale system is an emerging strategy for the realization of multifunctional materials. As a facile one-step process, ultrafast laser micromachining has emerged in recent years as a new technique for micro-nanostructure fabrication. In the past, lots of investigations on ultrafast laser micromachining were focused to understand the complex ablation mechanism, whereas recent works are mostly concerned with the fabrication of various metallic surface structures owing to their numerous potential functions, such as wetting, metallurgical and optical properties. This paper provides a short overview of advances in fabrication of functionalized metallic surfaces by ultrafast laser micromachining. The principles of interaction between ultrafast laser and metallic materials are provided. According to the surface topography, state-of-the-art knowledge on the fabrication of surface functionalization using ultrafast laser are presented. Functionalized properties of laser micro-machined metals are given. In addition, the challenges and outlooks in surface functionalized metals are presented.

We introduce optically clear and resilient free-form micro-optical components of pure (non-photosensitized) organic-inorganic SZ2080 material made by femtosecond 3D laser lithography (3DLL). This is advantageous for rapid printing of 3D micro-/nano-optics, including their integration directly onto optical fibers. A systematic study of the fabrication peculiarities and quality of resultant structures is performed. Comparison of microlens resiliency to continuous wave (CW) and femtosecond pulsed exposure is determined. Experimental results prove that pure SZ2080 is ∼20 fold more resistant to high irradiance as compared with standard lithographic material (SU8) and can sustain up to 1.91 GW/cm2 intensity. 3DLL is a promising manufacturing approach for high-intensity micro-optics for emerging fields in astro-photonics and atto-second pulse generation. Additionally, pyrolysis is employed to homogeneously shrink structures up to 40% by removing organic SZ2080 constituents. This opens a promising route towards downscaling photonic lattices and the creation of mechanically robust glass-ceramic microstructures.

Ultrafast laser technology has moved from ultrafast to ultra-strong due to the development of chirped pulse amplification technology. Ultrafast laser technology, such as femtosecond lasers and picosecond lasers, has quickly become a flexible tool for processing brittle and hard materials and complex micro-components, which are widely used in and developed for medical, aerospace, semiconductor applications and so on. However, the mechanisms of the interaction between an ultrafast laser and brittle and hard materials are still unclear. Meanwhile, the ultrafast laser processing of these materials is still a challenge. Additionally, highly efficient and high-precision manufacturing using ultrafast lasers needs to be developed. This review is focused on the common challenges and current status of the ultrafast laser processing of brittle and hard materials, such as nickel-based superalloys, thermal barrier ceramics, diamond, silicon dioxide, and silicon carbide composites. Firstly, different materials are distinguished according to their bandgap width, thermal conductivity and other characteristics in order to reveal the absorption mechanism of the laser energy during the ultrafast laser processing of brittle and hard materials. Secondly, the mechanism of laser energy transfer and transformation is investigated by analyzing the interaction between the photons and the electrons and ions in laser-induced plasma, as well as the interaction with the continuum of the materials. Thirdly, the relationship between key parameters and ultrafast laser processing quality is discussed. Finally, the methods for achieving highly efficient and high-precision manufacturing of complex three-dimensional micro-components are explored in detail.

Ultrafast lasers are proven and continually evolving manufacturing tools. Concurrently, additive manufacturing (AM) has emerged as a key area of interest for 3D fabrication of objects with arbitrary geometries. Use of ultrafast lasers for AM presents possibilities for next generation manufacturing techniques for hard-to-process materials, transparent materials, and micro- and nano-manufacturing. Of particular interest are selective laser melting/sintering (SLM/SLS), multiphoton lithography (MPL), laser-induced forward transfer (LIFT), pulsed laser deposition (PLD), and welding. The development, applications, and recent advancements of these technologies are described in this review as an overview and delineation of the burgeoning ultrafast laser AM field. As they mature, their adoption by industry and incorporation into commercial systems will be facilitated by process advancements such as: process monitoring and control, increased throughput, and their integration into hybrid manufacturing systems. Recent progress regarding these aspects is also reviewed.

An experimental study is presented to evaluate the influence of anisotropically shaped textures on the behaviour of sliding friction and sensitivity to sliding direction. The plate samples were textured with triangular sloped dimples using an ultrafast laser surface texturing technique. Reciprocating cylinder-on-plate tests were conducted with steel sliding pairs using mineral base oil as a lubricant to compare the tribological performance of reference non-textured specimen and dimpled samples. The dimples were designed with varying converging angles in the transverse y – z plane and top-view x – y plane. In this study, no dimple was fully covered in the contact area since the dimples size is much larger than the Hertzian line contact width. Stribeck style dynamic friction curves across boundary, mixed and hydrodynamic lubrication regimes were used to determine the benefit or antagonism of texturing. Observation of the directional friction effect of the anisotropic textures indicated that the converging shapes are beneficial for friction reduction, and the dimpled specimens have a lower friction coefficient particular under prevailing boundary lubrication conditions. It was also found that the real contact length variation rate is a major factor controlling the local friction response. The sloped bottoms of the textures produce effective converging wedge action to generate hydrodynamic pressure and contribute to the overall directional friction effects.