Femtosecond Laser Fabrication Research Articles

Femtosecond laser direct writing wedge metallic microcavities for terahertz sensing

Metallic resonators allow the manipulation of electromagnetic fields in subwavelength volumes for strong light-matter interaction, underpinning emerging flat-optics devices. Metamaterials designed with optimized effective mode volume (Veff) for stimulating and maximizing the utilization of high-density photons are highly desirable for sensing applications. Here, we demonstrate a bowtie-type terahertz (THz) metallic aperture metamaterial structure with low Veff for enhanced biosensing. The device leverages the inherent characteristic of the femtosecond laser fabrication process enabling wedge cavities down to 3 µm by tailoring the pulse energy, whose sensing performance is superior to trapezoidal ones. Such a substrate-free, microcavity metallic metamaterial sensor with extremely strong interactions achieves an experimentally normalized sensitivity of 0.654 RIU−1, and demonstrates the detection of L-proline down to 0.87 nmol. These findings provide new insights into the design and optimization of efficient THz metamaterials with tightly confined fields for ultrasensitive biomolecular detection.

Femtosecond laser fabrication of 3D vertically aligned micro-pore network on thick-film Li4Ti5O12 electrode for high-performance lithium storage

The development of energy storage devices with high energy density relies heavily on thick film electrodes, but it is challenging due to the limited ion transport kinetics inherent in thick electrodes. Here, we report on the preparation of a directional vertical array of micro-porous transport networks on LTO electrodes using a femtosecond laser processing strategy, enabling directional ion rapid transport and achieving good electrochemical performance in thick film electrodes. Various three-dimensional (3D) vertically aligned micro-pore networks are innovatively designed, and the structure, kinetics characteristics, and electrochemical performance of the prepared ion transport channels are analyzed and discussed by multiple characterization and testing methods. Furthermore, the rational mechanisms of electrode performance improvement are studied experimentally and simulated from two aspects of structural mechanics and transmission kinetics. The ion diffusion coefficient, rate performance at 60 C, and electrode interface area of the laser-optimized 60-15% micro-porous transport network electrodes increase by 25.2 times, 2.2 times, and 2.15 times, respectively than those of untreated electrodes. Therefore, the preparation of 3D micro-porous transport networks by femtosecond laser on ultra-thick electrodes is a feasible way to develop high-energy batteries. In addition, the unique micro-porous transport network structure can be widely extended to design and explore other high-performance energy materials.

Femtosecond Laser Direct Writing of Flexible Electronic Devices: A Mini Review.

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.

Femtosecond Laser Fabrication and Refractive Index Sensing Characteristics of Highly Sensitive Fiber Michelson Microcavity

Femtosecond Laser Fabrication and Refractive Index Sensing Characteristics of Highly Sensitive Fiber Michelson Microcavity

Femtosecond Laser Fabrication of Infrared Micro‑Optical Devices Based on Hard and Brittle Materials and Their Applications (Invited)

Femtosecond Laser Fabrication of Infrared Micro‑Optical Devices Based on Hard and Brittle Materials and Their Applications (Invited)

Atomistic-Continuum Study of an Ultrafast Melting Process Controlled by a Femtosecond Laser-Pulse Train.

In femtosecond laser fabrication, the laser-pulse train shows great promise in improving processing efficiency, quality, and precision. This research investigates the influence of pulse number, pulse interval, and pulse energy ratio on the lateral and longitudinal ultrafast melting process using an experiment and the molecular dynamics coupling two-temperature model (MD-TTM model), which incorporates temperature-dependent thermophysical parameters. The comparison of experimental and simulation results under single and double pulses proves the reliability of the MD-TTM model and indicates that as the pulse number increases, the melting threshold at the edge region of the laser spot decreases, resulting in a larger diameter of the melting region in the 2D lateral melting results. Using the same model, the lateral melting results of five pulses are simulated. Moreover, the longitudinal melting results are also predicted, and an increasing pulse number leads to a greater early-stage melting depth in the melting process. In the case of double femtosecond laser pulses, the pulse interval and pulse energy ratio also affect the early-stage melting depth, with the best enhancement observed with a 2 ps interval and a 3:7 energy ratio. However, pulse number, pulse energy ratio, and pulse interval do not affect the final melting depth with the same total energies. The findings mean that the phenomena of melting region can be flexibly manipulated through the laser-pulse train, which is expected to be applied to improve the structural precision and boundary quality.

Controllable multi-scale hydrophobic structures on titanium alloy by polarization-dependent femtosecond laser fabrication and magnetron sputtering

A significant challenge is to develop effective and controllable processes for fabricating hydrophobic metal surfaces with high mechanical properties. The combination of femtosecond laser direct writing (LDW) and gold nanoparticle magnetron sputtering (Au-MS) has successfully produced multiscale structures on Ti–6Al–4V (TC4) alloy, which possess excellent superhydrophobic and hardening properties. By adjusting the laser polarization to control micro/nanostructures, the dual-scale structure is transformed into a triple-scale structure, leading to a significant increase in the contact angle under proper scanning intervals. The Au-MS further fabricates a superhydrophobic surface, with a maximum contact angle of 153° and a minimum sliding angle of 4°. Surface hardness can be raised to 408 HV from 367 HV. This work reveals that the wetting mechanism for the dual-scale structures of TC4 alloy fabricated by laser direct writing is in the Cassie-Baxter state. While the triple-scale structures of Au-MS after linear polarization LDW (LPLDW) and the triple-scale structures of circular polarization LDW (CPLDW) with or without Au-MS are in Wenzel state, resulting in a different relationship between contact angle and surface structure. The flexible and high-efficiency fabrication of these multiscale structures has made TC4 alloy more competitive in self-cleaning and anti-freezing applications.

Single-Pixel-Adjustable Structural Color Fabricated Using a Spatially Modulated Femtosecond Laser.

Structural colors provide a highly stable and ecofriendly dyeing mechanism. The ability to adjust structural colors by a single pixel enhances their flexibility and application range. However, achieving single-pixel control and dynamic adjustment of structural colors remain a challenge yet. In this study, we propose a coloring method involving microcurve surfaces fabricated using a spatially modulated femtosecond laser hybrid technology, which combines spatially modulated femtosecond laser-assisted wet etching and molding. The fabricated microcurve surface exhibits bright colors under white light irradiation, and the color of each pixel can be adjusted independently by changing the morphology of the modified region inside fused silica using a femtosecond laser. With the high flexibility of femtosecond laser fabrication, color lightness can be accurately controlled through the quantitative adjustment of the arrangement of microcurve surfaces in an array, and various color patterns can be fabricated through the programmable arrangement of different microcurve surfaces. Additionally, the color exhibits strong dynamic characteristics, that is, different colors correspond to different external forces.

Femtosecond laser fabrication of silicon surface microstructures for enhanced infrared radiation under electric drive

Silicon surface microstructures can significantly improve their reflection and absorption characteristics and are widely used in photovoltaics and optoelectronic detection. But there is little research on the infrared emission characteristics of microstructure silicon since silicon is an indirect bandgap material. Here, we fabricate surface microstructures on highly doped silicon by femtosecond laser scanning, enhancing its broadband infrared radiation significantly under electric driving. At 12 μm, it can be enhanced to 274% of the untreated silicon. Our results show that silicon with surface microstructures can be used as a wideband infrared emitter. This study provides a new method for realizing a broad-spectrum silicon-based electrical drive infrared light source.

Defocus compensation scheme for femtosecond laser direct writing of large-area non-periodic micro-structures

The optical path error, the position-independent geometric error, and the form and position tolerance of the substrate will lead to position deviations of the laser focus resulting in the inconsistency of the large area micro-structure and limiting the processing range of the femtosecond laser fabrication platform. To realize continuous defocus compensation along the processing trajectory, an autofocus scheme consisting of an optimized depth from focus (DFF) method based on grid division and the bilinear interpolation algorithm is proposed in this paper. The optimized DFF method includes the Laplace-DWT evaluation function combining the advantages of spatial domain and frequency domain sharpness evaluation function, an adaptive focusing window selection method, and an adaptive step length three-step hill-climbing search method. The optimized DFF method was used to obtain the best focus position of each grid point. Compared with the traditional DFF method, the optimized algorithm has higher focusing precision and avoids the disadvantage of time-consuming focusing. Then, to compensate for interpolating points of the processing trajectory, the bilinear interpolation algorithm was introduced to achieve online focusing during two-photon lithography processing. Finally, the feasibility and effectiveness of the auto-focusing scheme were validated by experiments. Through defocus compensation, the sharpness evaluation value of the focus image on the processing trajectory improved by 90%, which indicated the successful focus of the laser beam on the workpiece surface. Moreover, a high-precision and large-area encoded micro-polarizer array with consistent structure were fabricated successfully. This paper provides a simple way to identify and compensate the defocus errors online with high accuracy and efficiency. The proposed method can improve the machining accuracy and quality of the femtosecond laser direct writing.

Femtosecond Laser Fabrication of SiC Microlens Arrays as Integrated Light Homogenizer and Splitter

Silicon carbide (SiC) plays a vital role in special optics because of its stable physicochemical and excellent optical properties; however, making the fabrication of SiC considerably more difficult. In this study, femtosecond laser-assisted inductively coupled plasma etching (ICP) technology is proposed to achieve the efficient fabrication of large-area microlens arrays on the surface of silicon carbide. As an illustration, the microlens array was used for high-quality beam homogenization (uniformity is up to 90%) of the transmitted and reflected Gaussian light beams with a wavelength of 532 nm. The beam-splitting ratio can be dynamically adjusted (from 1.2 to 3.2) by controlling the angle of the incident light, indicating that the SiC microlens arrays can act as an integrated optical homogenizer and beam splitter. This method demonstrates the broad application prospects of SiC in miniaturized and integrated special optics and provides new ideas for further applications of SiC in integrated optical systems.

Micro/nanostructured amorphous TiNbZr films to enhance the adhesion strength and corrosion behavior of stainless steel

To improve the corrosion resistance of key components and ensure the service safety of marine equipment, here we combined femtosecond (fs) laser fabrication and magnetron sputtering deposition to develop micro/nanostructured amorphous TiNbZr films. Analysis of the compositional, microstructural, corrosion, and mechanical properties was conducted. The results showed that the TiNbZr films were amorphous, and spherical TiNbZr nanoparticles uniformly covered the fs laser-induced periodic fringe structure. A complex hierarchical micro/nanostructure was formed that was hydrophobic and showed enhanced adhesion strength. The TiNbZr films deposited on fs laser-treated substrates provided the best corrosion resistance, showing a self-corrosion current density of 116 nA/cm2, excellent passive ability, and pitting resistance. The microscratch test revealed that the micro/nanostructures doubled the binding strength of the TiNbZr/316L interface due to the compositional and structural gradients induced by an approximately 20 nm transition layer formed during fs laser processing. This work provides a new method for obtaining anti-corrosion films with a high adhesion strength for marine applications.

Femtosecond Laser Fabrication of Curved Plasma Channels with Low Surface Roughness and High Circularity for Multistage Laser-Wakefield Accelerators.

A multistage laser-wakefield accelerator with curved plasma channels was proposed to accelerate electrons to TeV energy levels. In this condition, the capillary is discharged to produce plasma channels. The channels will be used as waveguides to guide intense lasers to drive wakefields inside the channel. In this work, a curved plasma channel with low surface roughness and high circularity was fabricated by a femtosecond laser ablation method based on response surface methodology. The details of the fabrication and performance of the channel are introduced here. Experiments show that such a channel can be successfully used to guide lasers, and electrons with an energy of 0.7 GeV were achieved.

Femtosecond laser fabrication of chirped and tilted fiber Bragg gratings for stimulated Raman scattering suppression in kilowatt-level fiber lasers.

Chirped and tilted fiber Bragg gratings (CTFBGs) are important all-fiber filtering components in high-power fiber lasers for stimulated Raman scattering (SRS) suppression. The fabrication of CTFBGs in large-mode-area double-cladding fibers (LMA-DCFs) by femtosecond (fs) laser is reported for the first time to the best of our knowledge. The chirped and tilted grating structure is obtained by scanning the fiber obliquely and moving the fs-laser beam relative to the chirped phase mask at the same time. By this method, the CTFBGs with different chirp rates, grating lengths, and tilted angles are fabricated, and the maximum rejection depth and bandwidth are ∼25 dB and ∼12 nm, respectively. To test the performance of the fabricated CTFBGs, one is inserted between the seed laser and the amplifier stage of a 2.7 kW fiber amplifier, and an SRS suppression ratio of ∼4 dB is achieved with no reduction in laser efficiency and degradation in beam quality. This work provides a highly fast and flexible method to fabricate large-core CTFBGs, which is of great significance to the development of high-power fiber laser systems.

Femtosecond laser fabrication of large-core fiber Bragg gratings for high-power fiber oscillators

In this paper, a fs-laser phase mask inscription system based on a galvanometer scanning strategy is designed and set up for the fabrication of large-core fiber Bragg gratings (FBGs). Based on this setup, a homogeneous cross-sectional refractive index modulation can be achieved in the core of a large-mode-area fiber, and a pair of FBGs are fabricated in fibers with a core diameter of 30 µm. To investigate the performance of the fabricated FBGs, a high power all-fiber oscillator is built using a pure backward pumping structure. The FBGs work well, and the maximum output power of 7920 W is achieved with an optical–optical conversion efficiency of 77.3%. To the best of our knowledge, this is the highest power of all-fiber oscillators based on fs-written FBGs. This work provides a flexible, stable, and economic scanning strategy for large-core FBG inscription and exhibits excellent performance for high power fiber lasers.

Emerging applications of femtosecond laser fabrication in neurobiological research.

As a typical micro/nano processing technique, femtosecond laser fabrication provides the opportunity to achieve delicate microstructures. The outstanding advantages, including nanoscale feature size and 3D architecting, can bridge the gap between the complexity of the central nervous system in virto and in vivo. Up to now, various types of microstructures made by femtosecond laser are widely used in the field of neurobiological research. In this mini review, we present the recent advancement of femtosecond laser fabrication and its emerging applications in neurobiology. Typical structures are sorted out from nano, submicron to micron scale, including nanoparticles, micro/nano-actuators, and 3D scaffolds. Then, several functional units applied in neurobiological fields are summarized, such as central nervous system drug carriers, micro/nano robots and cell/tissue scaffolds. Finally, the current challenges and future perspective of integrated neurobiology research platform are discussed.

Femtosecond Laser Fabrication of Anisotropic Structures in Phosphorus- and Boron-Doped Amorphous Silicon Films.

Femtosecond laser-modified amorphous silicon (a-Si) films with optical and electrical anisotropy have perspective polarization-sensitive applications in optics, photovoltaics, and sensors. We demonstrate the formation of one-dimensional femtosecond laser-induced periodic surface structures (LIPSS) on the surface of phosphorus- (n-a-Si) and boron-doped (p-a-Si) amorphous silicon films. The LIPSS are orthogonal to the laser polarization, and their period decreases from 1.1 ± 0.1 µm to 0.84 ± 0.07 µm for p-a-Si and from 1.06 ± 0.03 to 0.98 ± 0.01 for n-a-Si when the number of laser pulses per unit area increases from 30 to 120. Raman spectra analysis indicates nonuniform nanocrystallization of the irradiated films, with the nanocrystalline Si phase volume fraction decreasing with depth from ~80 to ~40% for p-a-Si and from ~20 to ~10% for n-a-Si. LIPSS' depolarizing effect, excessive ablation of the film between LIPSS ridges, as well as anisotropic crystalline phase distribution within the film lead to the emergence of conductivity anisotropy of up to 1 order for irradiated films. Current-voltage characteristic nonlinearity observed for modified p-a-Si samples may be associated with the presence of both the crystalline and amorphous phases, resulting in the formation of potential barriers for the in-plane carrier transport and Schottky barriers at the electric contacts.

Femtosecond laser fabrication and chemical coating of anti-corrosion ethylene-glycol repellent aluminum surfaces

Ethylene glycol (EG) is widely used as a cooling agent in factories, aviation, and automobiles. However, its corrosive nature can create significant damage and reduce the life cycle of devices. This paper compares three different methods to achieve the superhydrophobic anti-corrosion aluminum surfaces for working in an engine coolant environment. The methods are combinations between femtosecond laser fabrication and chemical coatings using Polydimethylsiloxane (PDMS) and Triethoxy-1H,1H,2H,2H-tridecafluoro-n-octylsilane (TTFOS). All the samples show superhydrophobicity with contact angles greater than 150°, and sliding angles smaller than 10°. The superhydrophobic surface (SHS) show the best corrosion rate up to three orders of magnitude compared to flat surfaces when working in an engine coolant environment. Moreover, corrosion inhibition efficiencies of the fabricated surfaces impress the best results greater than 98%. The anti-corrosion behavior of the SHS is explained. After comparing the performances of the surfaces fabricated by three methods, the most suitable method is proposed to produce anti-corrosion aluminum surfaces for applications using engine coolant as an environment.

Femtosecond laser fabrication and chemical coating of anti-corrosion ethylene-glycol repellent aluminum surfaces

Femtosecond laser fabrication and chemical coating of anti-corrosion ethylene-glycol repellent aluminum surfaces

Large-area cactus-like micro-/nanostructures with anti-reflection and superhydrophobicity fabricated by femtosecond laser and thermal treatment

In the face of an energy shortage, exploring surfaces with excellent photothermal conversion ability to effectively utilize solar energy may alleviate it. In this paper, combining the femtosecond laser fabrication and thermal treatment, a cactus-like hierarchical structure is presented. Its morphology, composition, and geometrical size distribution are characterized. The properties of anti-reflection, photothermal conversion, and superhydrophobicity are experimentally confirmed. Furthermore, based on numerical simulation, the light absorption mechanism of the hierarchical structure is elucidated. In addition, the origin of wettability is also explained. This fast fabrication method presented here would promote the large-scale industrial application of laser-processed photothermal conversion surfaces.