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Integrated photonics is attracting considerable attention and has found many applications in both classical and quantum optics, fulfilling the requirements for the ever-growing complexity in modern optical experiments and big data communication. Femtosecond (fs) laser direct writing (FLDW) is an acknowledged technique for producing waveguides (WGs) in transparent glass that have been used to construct complex integrated photonic devices. FLDW possesses unique features, such as three-dimensional fabrication geometry, rapid prototyping, and single step fabrication, which are important for integrated communication devices and quantum photonic and astrophotonic technologies. To fully take advantage of FLDW, considerable efforts have been made to produce WGs over a large depth with low propagation loss, coupling loss, bend loss, and highly symmetrical mode field. We summarize the improved techniques as well as the mechanisms for writing high-performance WGs with controllable morphology of cross-section, highly symmetrical mode field, low loss, and high processing uniformity and efficiency, and discuss the recent progress of WGs in photonic integrated devices for communication, topological physics, quantum information processing, and astrophotonics. Prospective challenges and future research directions in this field are also pointed out.

Diverse natural organisms possess stimulus-responsive structures to adapt to the surrounding environment. Inspired by nature, researchers have developed various smart stimulus-responsive structures with adjustable properties and functions to address the demands of ever-changing application environments that are becoming more intricate. Among many fabrication methods for stimulus-responsive structures, femtosecond laser direct writing (FsLDW) has received increasing attention because of its high precision, simplicity, true three-dimensional machining ability, and wide applicability to almost all materials. This paper systematically outlines state-of-the-art research on stimulus-responsive structures prepared by FsLDW. Based on the introduction of femtosecond laser-matter interaction and mainstream FsLDW-based manufacturing strategies, different stimulating factors that can trigger structural responses of prepared intelligent structures, such as magnetic field, light, temperature, pH, and humidity, are emphatically summarized. Various applications of functional structures with stimuli-responsive dynamic behaviors fabricated by FsLDW, as well as the present obstacles and forthcoming development opportunities, are discussed. Fundamentals of femtosecond laser–matter interaction are presented. Fabrication strategies based on femtosecond laser direct writing are reviewed. Diverse stimulus-responsive structures by femtosecond laser direct writing are summarized. Functional applications of these stimulus-responsive structures are discussed.

Femtosecond laser direct writing (FLDW) has been widely employed in controllable manufacturing of biomimetic micro/nanostructures due to its specific advantages including high precision, simplicity, and compatibility for diverse materials in comparison with other methods (e.g. ion etching, sol-gel process, chemical vapor deposition, template method, and self-assembly). These biomimetic micro/nanostructured surfaces are of significant interest for academic and industrial research due to their wide range of potential applications, including self-cleaning surfaces, oil-water separation, and fog collection. This review presents the inherent relationship between natural organisms, fabrication methods, micro/nanostructures and their potential applications. Thereafter, we throw a list of current fabrication strategies so as to highlight the advantages of FLDW in manufacturing bioinspired microstructured surfaces. Subsequently, we summarize a variety of typical bioinspired designs (e.g. lotus leaf, pitcher plant, rice leaf, butterfly wings, etc) for diverse multifunctional micro/nanostructures through extreme femtosecond laser processing technology. Based on the principle of interfacial chemistry and geometrical optics, we discuss the potential applications of these functional micro/nanostructures and assess the underlying challenges and opportunities in the extreme fabrication of bioinspired micro/nanostructures by FLDW. This review concludes with a follow up and an outlook of femtosecond laser processing in biomimetic domains.

By virtue of its narrow pulse width and high peak power, the femtosecond pulsed laser can achieve high-precision material modification, material additive or subtractive, and other forms of processing. With additional good material adaptability and process compatibility, femtosecond laser-induced application has achieved significant progress in flexible electronics in recent years. These advancements in the femtosecond laser fabrication of flexible electronic devices are comprehensively summarized here. This review first briefly introduces the physical mechanism and characteristics of the femtosecond laser fabrication of various electronic microdevices. It then focuses on effective methods of improving processing efficiency, resolution, and size. It further highlights the typical progress of applications, including flexible energy storage devices, nanogenerators, flexible sensors, and detectors, etc. Finally, it discusses the development tendency of ultrashort pulse laser processing. This review should facilitate the precision manufacturing of flexible electronics using a femtosecond laser.

Laser direct writing is a highly promising method for material fabrication due to its simplicity, design flexibility, and ability to create complex structures that are difficult to achieve with conventional etching techniques. However, despite these advantages, it is currently not suitable for the growth of monocrystalline silicon, a key material in microelectronics with significant production value. This limitation arises from the use of low-order silane molecules or solid silicon particles in conventional laser direct writing processes. These feedstocks require high decomposition or melting energies and exhibit complex crystallization behavior during growth. As a result, the process typically yields only polycrystalline or amorphous silicon, thereby hindering its ability to meet the stringent performance requirements of highperformance electronic devices. In this study, laser direct writing of monocrystalline silicon was successfully achieved using an unconventional high-order liquid silane feedstock with high reactivity at low temperatures. A systematic comparison was conducted to evaluate the performance differences between low-order and high-order liquid silanes in the laser direct writing of monocrystalline silicon. The results indicate that the high-order liquid silane, cyclohexasilane (CHS), offers significant advantages in terms of silicon growth rate and the laser energy threshold required for growth. Furthermore, by dissolving white phosphorus in CHS, this study successfully achieved efficient in-situ doping of monocrystalline silicon. This approach not only avoids the use of highly toxic phosphorus sources (e.g., PH3) but also simplifies the doping process, offering a new strategy for low-damage, high-precision doping in semiconductor device fabrication. Overall, this study highlights the processing advantages of CHS in silicon-based micro- and nanofabrication and provides a valuable reference for new semiconductor manufacturing technologies.

A ratiometric self-powered photoelectrochemical sensor based on laser direct writing technology was constructed to address the problem that the conventional single-signal detection mode was susceptible to the influence of instrumentation and environmental factors, which interfered with the detection results. Laser-induced CdS/TiO 2 /Graphene was prepared as dual photoanodes (PA1 and PA2), which were controlled by multiplexed switches to form a photocatalytic fuel cell with Pt cathode. By modifying the aptamer of aflatoxin B1 (AFB1) on the photoanode surface, the target was specifically captured to the electrode surface to form a biological complex, which increased the steric hindrance and affected the electron transfer, thus reducing the output signal of the sensor. Targets with different concentrations were incubated on the surface of PA1, and targets with fixed concentrations were incubated on the surface of PA2. Under the control of the multiplex switch, the output signals of the two photoanodes were recorded, and the ratio of these two signals was used as the basis for the quantitative detection of AFB1. The sensor output was linearly increasing with the logarithm of AFB1 concentration from 1.0 to 150 ng mL −1 and the detection limit was 0.0974 ng mL −1 . Additionally, this method had good stability, fast response, and good selectivity to real samples, providing an effective method for food safety monitoring. Graphical Abstract

Recently, ultrafast laser direct writing has become an effective method for preparing flexible films with micro-nano structures. However, effective control of laser parameters to obtain acceptable micro-nano structures and the effect of micro-nano structure sizes on function of the film remain challenges. Additionally, flexible films with high X-band transmittance are urgently required in aerospace and other fields. In this work, we evaluate the feasibility of applying picosecond laser direct writing for fabricating micro-nano structures on the surface of flexible thin film and the relationship between the size of square columnar micro-nano structures and the transmittance of the flexible thin film. The results show that an array of square columnar micro-nano structures was achieved by picosecond laser direct writing on the surface of flexible thin film (Au-SiO2-PI) with a thickness of 50 µm. Additionally, excellent micro-nano structures morphology of the square columnar arrays without burning through or destroying were obtained by laser direct writing with a pulse power and frequency of 2 W and 100 KHz, respectively. The results also show that the X-band transmittance was effected by the characteristic of the square columnar array on the surface of the flexible thin film. The X-band transmittance was significantly increased by decreasing the length of the square column on the surface of the flexible thin film. The X-band transmittance was slightly increased by decreasing the width of the groove of the square column on the surface of the flexible thin film.

Polymer materials exhibit unique properties in the fabrication of optical waveguide devices, electromagnetic devices, and bio-devices. Direct laser writing (DLW) technology is widely used for micro-structure fabrication due to its high processing precision, low cost, and no need for mask exposure. This paper reviews the latest research progresses of polymer-based micro/nano-devices fabricated using the DLW technique as well as their applications. In order to realize various device structures and functions, different manufacture parameters of DLW systems are adopted, which are also investigated in this work. The flexible use of the DLW process in various polymer-based microstructures, including optical, electronic, magnetic, and biomedical devices are reviewed together with their applications. In addition, polymer materials which are developed with unique properties for the use of DLW technology are also discussed.

Organic room temperature phosphorescence (RTP) materials have potential applications in information technology and bioimaging. However, the precise control of the afterglow in reversible manners remains challenging for organic matters. Here, we report a kind of organic RTP material fabricated by simple heating mixtures of tartaric acid (TA) and aromatic acids, which can switch their phosphorescence by laser. Those mixtures show tunable phosphorescence from indigo to orange with phosphorescence efficiency of up to 53.99% due to locking different organic luminogens by the TA-formed matrix through the non-covalent interactions. The afterglow of those materials lasts a few seconds and disappears by water fumigation, which can be repeated in response to wet/heat stimuli. With drop-casting those materials on glass slides, a laser-repatternable phosphorescence is achieved by facile laser direct writing and quenched by water cyclically. Those results open the opportunity for the design of smart stimuli-responsive phosphorescence materials from sustainable natural products.

Titanium (Ti)-based implants are widely used for bone injuries but suffer from poor bioactivity. To address this, we propose an innovative synergistic approach that combines laser melting deposition (LMD) for the fabrication of titanium-based supports with laser direct writing via two-photon polymerization (LDW via TPP) for their functionalization with 3D polymeric microstructures. We functionalized Ti surfaces fabricated by LMD using Ti (99.85 wt.%) and TiC powders (79.95 wt.% Ti, 20.05 wt.% C), with 3D microstructures obtained by LDW via TPP. The 3D microstructures were made of IP-Dip photopolymer and comprised 64 vertical microtubes arranged in five layers (10 to 170 μm tall, >94% porosity). When seeded with MG-63 osteoblast-like cells, the Ti-based surfaces functionalized with 3D polymeric microstructures promoted 3D cells’ spatial organization. Moreover, the cells seeded on functionalized Ti-based surfaces showed earlier organic matrix synthesis (day 7 vs. day 14) and mineralization (higher deposits of calcium and phosphorus, starting from day 7), as compared with the cells from non-functionalized Ti. In addition, the traction forces exerted by the cells on the 3D microstructures, determined using FEBio Studio software, were of the order of hundreds of µN, whereas if the cells would have been seeded on extracellular matrix-like materials, the traction forces would have been of only few nN. These results point towards the major role played by 3D polymeric microarchitectures in the interaction between osteoblast-like cells and Ti-based surfaces. Overall, the functionalization of Ti-based constructs fabricated by LMD with 3D polymeric microstructures made by LDW via TPP significantly improved Ti bioactivity.