Search Results (111)

In this study, a facile and mask-free femtosecond laser direct writing (FLDW) approach is proposed to fabricate porous graphene (FLIG) patterns directly on polyimide (PI) substrates. By systematically adjusting the laser scanning spacing (10–25 μm), denser and more continuous microstructures are obtained, resulting in significantly enhanced thermal sensitivity. The optimized sensor demonstrated a temperature coefficient of 0.698% °C⁻¹ within the range of 40–120 °C, with response and recovery times of 10.3 s and 20.9 s, respectively. Furthermore, it exhibits remarkable signal stability across multiple thermal cycles, a testament to its reliability in extreme conditions. Moreover, the sensor was successfully integrated into a 3D-printed robotic platform, achieving both contact and non-contact temperature detection. These results underscore the sensor’s practical adaptability for real-time thermal sensing. This work presents a viable and scalable methodology for fabricating high-performance FLIG-based flexible temperature sensors, with extensive application prospects in wearable electronics, electronic skin, and intelligent human–machine interfaces. Full article

Color centers in solids, such as nitrogen-vacancy (NV) centers in diamonds, have gained significant attention in recent years due to their exceptional properties for quantum sensing. In this work, we demonstrate an NV center-based temperature sensor integrated into an optical waveguide to enable internal temperature sensing. A surface-cladding optical waveguide was fabricated in a diamond wafer containing NV centers using femtosecond laser direct writing. By analyzing the resonant peaks of optically detected magnetic resonance (ODMR) spectra, we established a precise correlation between temperature changes induced by the pump laser and shifts in the ODMR peak positions. This approach enabled temperature monitoring with a sensitivity of 1.1 $\mathrm{mK}/\sqrt{\mathrm{Hz}}$. These results highlight the significant potential of color centers in solids for non-contact, micro-scale temperature monitoring. Full article

We demonstrate the fabrication of the fiber Bragg grating (FBG) in a self-developed Yb-doped seven-core fiber using two femtosecond laser direct writing methods: a grating array inscription method and a plane-by-plane inscription method. The array fabrication method uses the femtosecond laser to directly write a parallel fiber grating array in the core. The plane-by-plane method is implemented by adding a diaphragm in the optical path to precisely control the length of the refractive index modulation line along the femtosecond laser incident direction. Combined with femtosecond laser scanning, a uniform refractive index modulation plane can be inscribed in the core in a single scanning. Based on these methods, we successfully fabricate high-quality high-reflection FBGs and chirped FBGs in each core of the large-core multicore fiber (MCF) with 14 μm core diameters. Both fabrication methods achieve FBGs with reflectivity above 97% at the central wavelength. We report for the first time the fabrication of high-quality, high-reflectivity FBGs in large-core Yb-doped seven-core fibers using the femtosecond laser plane-by-plane inscription method. This work provides a feasible scheme for fabricating FBGs in MCF. Full article

Perovskite quantum dots (PQDs), with their excellent optical properties, have become a leading semiconductor material in the field of optoelectronics. However, to date, it has been a challenge to achieve the three-dimensional high-resolution patterning of perovskite quantum dots. In this paper, an in situ femtosecond laser-direct-writing technology was demonstrated for three-dimensional high-resolution patterned CsPbBr₃ PQDs using a two-photon photoresist nanocomposite doped with the CsPbBr₃ perovskite precursor. By adjusting the laser processing parameters, the minimum line width of the PQDs material was confirmed to be 98.6 nm, achieving a sub-100 nm PQDs nanowire for the first time. In addition, the fluorescence intensity of the laser-processed PQDs can be regulated by the laser power. Our findings provide a new technology for fabricating high-resolution display devices based on laser-direct-writing CsPbBr₃ PQDs materials. Full article

Inspired by the ventral scale structure of the oriental sand boa, this study successfully fabricated multiscale bioinspired alumina (Al₂O₃) ceramics by combining the excellent mechanical properties, high-temperature resistance, and high hardness of ceramic composites with direct ink writing (DIW) 3D printing technology and femtosecond laser processing. A MoS₂ thin film was then deposited on the ceramic surface via radio frequency magnetron sputtering (PVD) to systematically investigate the impact of bioinspired structures on the tribological properties of ceramic composites under both dry and lubricated conditions. Experimental results demonstrated that bioinspired structures at different scales exhibited significant friction-reducing and wear-resistant characteristics compared to blank structures. Specifically, under room-temperature conditions, the friction coefficients of bioinspired ceramic composites with solid lubricants and oil lubrication were 0.3 and 0.148, respectively, indicating excellent tribological performance. These findings confirm the synergistic lubrication effect between bioinspired structures, two-dimensional solid lubricants, and lubricating oil, which significantly enhanced the friction-reducing and wear-resistant properties of ceramic components. Therefore, the synergistic design of multiscale bioinspired structures and solid lubricants provides an innovative strategy for the advanced application of ceramic components. Full article

Carbon-based nanomaterials with excellent electrical and optical properties are highly sought after for a plethora of hybrid applications, ranging from advanced sustainable energy storage devices to opto-electronic components. In this contribution, we examine in detail the dependence of electrical conductivity and the ultrafast optical nonlinearity of graphene oxide (GO) films on their degrees of reduction, as well as the link between the two properties. The GO films were first synthesized through the vacuum filtration method and then reduced partially and controllably by way of femtosecond laser direct writing with varying power doses. Subsequently, the four-point probe measurements of the reduced-GO (r-GO) films were demonstrated to exhibit superior resistivity and electrical conductivity compared with the pristine-GO counterpart. It was found that the conductivity of the film increases and then decreases with increasing ablation laser power (P), and GO was completely reduced at P = 100 mW, with a resistivity and electrical conductivity of 1.09 × 10⁻³ Ω·m and 9.19 × 10² S/m, respectively. GO was over-reduced at P = 120 mW, with its resistivity and electrical conductivity being 3.72 × 10⁻³ Ω·m and 2.69 × 10² S/m, respectively. We further tested the ultrafast optical nonlinearity (ONL) of the as-prepared pristine and reduced GO with the femtosecond Z-scan technique. The results show that the behavior of ONL is reversed whenever GO is reduced in a controlled manner. More interestingly, the higher the ablation laser power is, the stronger the optical nonlinearity of r-GO is. In particular, the nonlinear absorption and refraction coefficients of the r-GO films reach up to 3.26 × 10⁻⁸ m/W and −1.12 × 10⁻¹³ m²/W when P = 120 mW. The nonlinear absorption and refraction coefficients reach 1.9 × 10⁻⁸ m/W and −3 × 10⁻¹³ m²/W, respectively, for P = 70 mW. GO/r-GO thin films with tunable photovoltaic response properties have potential for a wide range of applications in microelectronic circuits, energy, and environmental sustainability. Full article

Microfluidic sensors incorporated onto chips allow sensor miniaturization and high-throughput analyses for point-of-care or non-clinical analytical tools. Three-dimensional (3D) printing based on femtosecond laser direct writing (fs-LDW) is useful for creating 3D microstructures with high spatial resolution because the structures are printed in 3D space along a designated laser light path. High-performance biochips can be fabricated using the ‘ship-in-a-bottle’ integration technique, in which functional microcomponents or biomimetic structures are embedded inside closed microchannels using fs-LDW. Solutions containing protein biomacromolecules as a precursor can be used to fabricate microstructures that retain their native protein functions. Here, we demonstrate the ship-in-a-bottle integration of pure 3D proteinaceous microstructures that exhibit pH sensitivity. We fabricated proteinaceous mesh structures with gap sizes of 10 and 5 μm. The sizes of these gaps changed when exposed to physiological buffers ranging from pH of 4 to 10. The size of the gaps in the mesh can be shrunk and expanded repeatedly by changing the pH of the surrounding buffer. Fs-LDW enables the construction of microscopic proteinaceous meshes that exhibit dynamic functions such as pH sensing and might find applications for filtering particles in microfluidic channels. Full article

In this work, we propose a fiber Bragg grating (FBG)-based sensor for curvature measurements. Two gratings are inscribed through the protective coating in a specialty optical fiber using focused femtosecond laser pulses and point-by-point direct writing technology. One grating is inscribed on the central core adjacent to an air channel, while the other is inscribed on the eccentric core. The bending characteristics of the two-core fiber strongly depend on the bending direction due to the asymmetry of the fiber cores. A bending sensitivity of 58 $\mathrm{p}\mathrm{m}/{\mathrm{m}}^{-1}$ is achieved by the FBG in the eccentric fiber core over the curvature range of 0–50 ${\mathrm{m}}^{-1}$. Temperature and humidity cross-sensitivity could be significantly reduced by analyzing the differences in peak shifts between the two gratings. The sensor features a large sensing range and good robustness due to the presence of its protective buffer coating, which makes it a good candidate for curvature sensing in engineering fields. Full article

Bubble printing is a patterning method in which particles are accumulated by the convection of bubbles generated by laser focusing. It is attracting attention as a method that enables the high-speed, high-precision patterning of various micro/nanoparticles. Although the bubble printing method is used for metallic particles and organic particles, most reports have focused on the patterning of solid particles and not on the patterning of liquid particles. In this study, liquid metal wiring patterns were fabricated using a bubble printing method in which eutectic gallium‒indium alloy (EGaIn) colloidal particles (≈diameter 0.7 µm) were fixed on a glass substrate by generating microbubbles through heat generation by focusing a femtosecond laser beam on the EGaIn colloidal particles. The wiring was then made conductive by replacing gallium oxide, which served as a resistance layer on the surface of the EGaIn colloidal particles, with silver via galvanic replacement. Fine continuous lines of liquid metal colloids with a line width of 3.4 µm were drawn by reducing the laser power. Liquid metal wiring with a conductivity of ≈1.5 × 10⁵ S/m was formed on a glass substrate. It was confirmed that the conductivity remained consistent even when the glass substrate was bent to a curvature of 0.02 m⁻¹. Full article

This review focuses on the innovative use of laser techniques in developing and functionalizing biomimetic surfaces, emphasizing their potential applications in the medical and biological fields. Drawing inspiration from the remarkable properties of various natural systems, such as the water-repellent lotus leaf, the adhesive gecko foot, the strong yet lightweight spider silk, and the unique optical structures of insect wings, we explore the potential for replicating these features through advanced laser surface modifications. Depending on the nature and architecture of the surface, particular techniques have been designed and developed. We present an in-depth analysis of various methodologies, including laser ablation/evaporation techniques, such as Pulsed Laser Deposition and Matrix-Assisted Pulsed Laser Evaporation, and approaches for laser surface structuring, including two-photon lithography, direct laser interference patterning, laser-induced periodic surface structures, direct laser writing, laser-induced forward transfer, and femtosecond laser ablation of metals in organic solvents. Additionally, specific applications are highlighted with the aim of synthesizing this knowledge and outlining future directions for research that further explore the intersection of laser techniques and biomimetic surfaces, paving the way for advancements in biomedical applications. Full article

The femtosecond laser direct writing of metals has gained significant attention for micro/nanostructuring. Copper (I) oxide nanospheres (NSs), a promising material for multi-photon metallization, can be reduced to copper (Cu) and sintered through near-infrared femtosecond laser pulse irradiation. In this study, we investigated the size effect of copper (I) oxide nanospheres on their morphology when coated on Cu thin films and irradiated by near-infrared femtosecond laser pulses. Three Cu₂O NS inks were prepared, consisting of small (φ100 nm), large (φ200 nm), and a mixture of φ100 nm and φ200 nm NSs. A unique phenomenon was observed at low laser pulse energy: both sizes of NSs bonded as single layers when the mixed NSs were used. At higher pulse energies, the small NSs melted readily compared to the large NSs. In comparisons between the large and mixed NSs, some large NSs remained intact, suggesting that the morphology of the NSs can be controlled by varying the concentration of different-sized NSs. Considering the simulation results indicating that the electromagnetic fields between large and small NSs are nearly identical, this differential morphology is likely attributed to the differences in the heat capacity of the NSs. Full article

In this paper, multifunctional, multilevel phase plates of quartz substrate were efficiently prepared by using a newly developed polygon scanner-based femtosecond laser photolithography system combined with inductively coupled discharge plasma reactive-ion etching (ICP-RIE) technology. The femtosecond laser photolithography system can achieve a scanning speed of 5 m/s and a preparation efficiency of 15 cm²/h while ensuring an overlay alignment accuracy of less than 100 nm and a writing resolution of 500 nm. The ICP-RIE technology can control the etching depth error within ±5 nm and the mask-to-mask edge error is less than 1 μm. An 8-level Fresnel lens phase plate with a focal length of 20 mm and an 8-level Fresnel axicon phase plate with a cone angle of 5° were demonstrated. The diffraction efficiency was greater than 93%, and their performance was tested for focusing and glass cutting, respectively. Combined with the high-speed femtosecond laser photolithography system’s infinite field-of-view (IFOV) processing capability, the one-time direct writing preparation of phase plate masks of different sizes was realized on a 6-inch wafer. This is expected to reduce the production cost of quartz substrate diffractive optical elements and promote their customized mass production. Full article

Ultrafast lasers, characterized by femtosecond and picosecond pulse durations, have revolutionized material processing due to their high energy density and minimal thermal diffusion, and have played a transformative role in precision manufacturing. This review first traces the progression from early ruby lasers to modern titanium–sapphire lasers, highlighting breakthroughs like Kerr-lens mode-locking and chirped pulse amplification. It also examines the interaction mechanisms between ultrafast pulses and various materials, including metals, dielectrics, and semiconductors. Applications of ultrafast lasers in microstructure processing techniques are detailed, such as drilling, cutting, surface ablation, and nano welding, demonstrating the versatility and precision of the technology. Additionally, it covers femtosecond laser direct writing for optical waveguides and the significant advancements in imaging and precision measurement. This review concludes by discussing potential future advancements and industrial applications of ultrafast lasers. Full article

We demonstrate high-extraction-rate Ta₂O₅-core/SiO₂-clad photonic waveguides on silicon fabricated by the photolithography-assisted chemo-mechanical etching technique. Low-confinement waveguides of larger than 70% coupling efficiency with optical fibers and medium propagation loss around 1 dB/cm are investigated in the experiment. Monolithic microring resonators based on Ta₂O₅ waveguides have shown the quality factors to be above 10⁵ near 1550 nm. The demonstrated Ta₂O₅ waveguides and their fabrication method hold great promise in various cost-effective applications, such as optical interconnecting and switching. Full article

Vibration sensors are widely applied in the detection of faults and analysis of operational states in engineering machinery and equipment. However, commercial vibration sensors with a feature of high hardness hinder their usage in some practical applications where the measured objects have irregular surfaces that are difficult to install. Moreover, as the operating environments of machinery become increasingly complex, there is a growing demand for sensors capable of working in wet and humid conditions. Here, we present a flexible, superhydrophobic vibration sensor with parallel microcracks. The sensor is fabricated using a femtosecond laser direct writing ablation strategy to create the parallel cracks on a PDMS film, followed by spray-coating with a conductive ink composed of MWCNTs, CB, and PDMS. The results demonstrate that the developed flexible sensor exhibits a high-frequency response of up to 2000 Hz, a high acceleration response of up to 100 m/s², a water contact angle as high as 159.61°, and a linearity of 0.9812 between the voltage signal and acceleration. The results indicate that the sensor can be employed for underwater vibration, sound recognition, and vibration monitoring in fields such as shield cutters, holding significant potential for mechanical equipment vibration monitoring and speech-based human–machine interaction. Full article