Published papers

Latent fingerprints (LFPs) are pivotal evidence in criminal investigations, yet their direct observation poses inherent challenges, necessitating advanced visualization techniques. Here, an innovative one-step laser-based methodology is presented for the rapid and accurate visualization of LFPs on metal surfaces. Gray value analysis is utilized to compare the optical contrast between the ridges and valleys of original and visualized fingerprints. Additionally, an orientation field method is employed to evaluate the texture quality of visualized fingerprints. The results demonstrate that laser irradiation significantly enhances the recognizability and pattern fidelity of LFPs by inducing differential oxide deposition: ridges, enriched in skin secretions, exhibit reduced oxide accumulation compared to valleys, thereby amplifying ridge-valley optical contrast. Furthermore, the visualized fingerprints exhibit excellent resistance to abrasion. Importantly, this method demonstrates broad applicability across surfaces with varying roughness levels and diverse metal types. This study establishes a robust and versatile tool for the rapid and accurate visualization of LFPs, offering transformative potential for forensic investigations.

High-end optical molds are essential for mass-producing precision optical components used in biomedical, defense, and automotive manufacturing applications. These components are often produced through single-point diamond turning (SPDT), and their optical performance depends on their surface quality and shape accuracy. On mirror-grade surfaces, periodic microstructures caused by feed rate variations and tool wear can induce diffraction, leading to visible rainbow diffraction fringes that degrade optical performance. In traditional surface metrology, inspections of diffraction fringes require visual or laser-based methods, which are labor-intensive, time-consuming, and heavily reliant on human judgment and experience. To improve the efficiency of quality inspection, this study developed a fast Fourier transform (FFT)-based method to assess diffraction intensity. A full-factorial experiment was performed to analyze the effects of feed rate and tool wear on diffraction intensity, with the FFT employed to extract surface periodic features. The experimental results indicated that greater tool wear led to higher diffraction intensity, with the second harmonic of the FFT response being strongly correlated with diffraction intensity (K > 0.89) under 650-nm laser illumination. Analysis of the theoretical diffraction angle confirmed that the second harmonic was the main cause of diffraction, with the positional accuracy of theoretical diffraction spots exceeding 90 %. When the second harmonic response exceeded the surface roughness threshold, imaging quality was negatively affected. The proposed innovative FFT-based approach enabled rapid diffraction assessment, assists in tool wear monitoring and reducing quality inspection time by 65 % compared with traditional laser-based inspection methods. Thus, this method has high potential for application in quality inspections in SPDT.

Double-margin drills are expected to provide radial stability and Ultrasonic-Assisted Drilling (UAD) can reduce cutting forces and torque, but the academic literature on double-margin drills is limited, and their combined effect with UAD is not well understood. To investigate this interactive effect, this paper analyzes the geometric accuracy of holes in Aluminum 7075-T6 using a full factorial design of experiments. The influence of drill margin, ultrasonic-assistance, spindle speed, and feed rate on hole cylindricity and circularity errors at entry and exit were analyzed. Analysis of Variance is used to identify which factors and interactions are statistically significant. The most significant factor affecting the hole cylindricity error was a strong interaction between the drill margin and the spindle speed. The use of double-margin drills improved the cylindricity by 44% at low speed compared with using single-margin drills. However, the use of double-margin drill degraded the cylindricity by 29% at high speed. For the hole circularity, single-margin drills consistently provided a good performance, while applying UAD was often detrimental particularly when combined with double-margin drills. Furthermore, the exit circularity errors were approximately double those at the entry, highlighting the significant instability of the drill at breakthrough phase. The results revealed complex and often conflicting interactions. To model and accurately predict the conflicting interaction and non-linear behavior, a series of Adaptive Neuro-Fuzzy Inference System models were developed and validated. The central conclusion is that a universal optimization is inadequate; this paper provides both the statistical proof and the predictive models necessary for a criteria-based approach, where parameters are selected based on the single most critical geometric feature.

The surface modification is imperative to mitigate defect-induced degradation and ensure the long-term structural integrity of Zr-4 alloys operating in extreme nuclear reactor environments. However, conventional surface modification of Zr-4 alloys is inherently constrained by the inseparable coupling of thermal and chemical kinetics. To disentangle these respective roles, we employ an orthogonal modulation strategy comprising three distinct pathways: laser processing in argon to examine thermal effects in the absence of chemical reactivity, gas nitriding to emphasize chemical contributions with minimal thermal input, and laser nitriding to achieve synergistic thermo-chemical coupling. The results demonstrate that thermal activation alone induces moderate hardening (3.5 GPa) through grain refinement, whereas solid-state chemical diffusion during gas nitriding yields substantial hardening (14.8 GPa) via defect annihilation and interstitial solid-solution formation. Critically, the synergistic integration of both factors in laser nitriding produces a further amplified hardness (23.5 GPa). This pronounced reinforcement arises from ZrN precipitation, which triggers pronounced grain refinement and promotes deep densification via consumption of reactive gas species. These findings provide a mechanistic basis for designing high-performance Zr-4 alloy components.

Electrical discharge machining (EDM) is widely used to machine hard materials, such as tungsten carbide; however, the machining rate and surface quality are low. In this research, the effects of mixing electrically conductive carbon nanofiber (CnF), semiconductive silicon (Si) powder, and insulative alumina powder (Al2O3) at different concentrations in a dielectric fluid were studied by observing single discharge craters and hole machining performance in the EDM of ultrafine particle type tungsten carbide. Craters obtained using carbon nanofiber and alumina were much smaller than in oil-only conditions. In contrast, The results show that adding CnF significantly improved the material removal rate under all conditions. Si and Al2O3 powders only improved the machining performance at a high discharge energy of 110 V. Furthermore, improvement in surface roughness was observed prominently at high voltages for all the powders. Among the three powders, alumina was found to improve the surface roughness the most.

The batch mode electrical discharge machining (EDM) method has been developed to improve the throughput and accuracy in fabricating array structures, but the process suffers from insufficient debris removal caused by the complex electrode geometry. Tool vibration has been used to improve flushing conditions, but to date the underlying mechanism of the tool vibration on the micro EDM of array structures remains unclear. This study aimed to investigate the effect of tool vibration on the machining process by direct observation of the discharge phenomena in the discharge gap by using a high-speed camera. Micro EDM experiments using 9 and 25 array electrodes were performed, and the effect of tool vibration on the discharge uniformity and tool wear was evaluated. It was found that tool vibration improved the uniformity of the discharge distribution, increased the machining efficiency, and suppressed the tool wear. The discharges occurred in periodic intervals, and the intensity increased with the amplitude of tool vibration. The results of this study indicate that the vibration parameters determine the discharge period duration and intensity to achieve optimum stability and efficiency of the machining process.

Flexible and controllable fabrication of micro–nano structures on metallic glasses (MGs) endow them with more functional applications, but it is still challenging due to the unique mechanical, physical, and chemical properties of MGs. In this study, inspired by a new physical phenomenon observed in the nanosecond laser–MG interaction (i.e., the surface structure is transformed from the normally observed microgroove into the micro–nano bulge at a critical peak laser power intensity), a nanosecond laser “pulling” method is proposed to pattern the MG surface. The formation mechanism and evolution of the micro–nano bulge are investigated in detail, and accordingly, various micro–nano structures including the unidirectional stripe, pillar, cross-hatch patterns, “JLU”, circle, triangle, and square, are derived and created on the MG surface, which affects the surface optical diffraction. Overall, this study provides a highly flexible and controllable method to fabricate micro–nano structures on MGs.

Cutting and abrasive processes affect the surface layer state of the components treated. This determines their performance in service. An adjustment of the surface layer properties would allow for enhanced performance. This paper introduces the influences of named processes on the surface layer state and their systematics. Models and sensor concepts for surface conditioning are described and combined to soft sensors which are the basis for active control within the processes. A validation study and actual applications of the conditioning concept are shown, allowing for further technological and scientific understanding of surface conditioning and its contribution to material and energy efficiency.

In recent years, large-aperture additively-manufactured metal mirrors have been widely used in optics, astronomy, and aerospace. However, achieving precision diamond cutting of these mirrors remains challenging due to their intrinsic non-uniform lightweight structures. On-machine measurement of surface errors and compensation cutting offer promising solutions; however, current techniques for large-aperture metal mirrors remain insufficiently mature. Furthermore, compensation cutting is hindered by the coupling of multiple error factors, including inherent equipment errors, measurement uncertainties, and surface fitting deviations. To address these challenges, this study developed an on-machine measurement system combined with a compensation cutting method based on Zernike polynomials. Unlike compensating for the entire surface error, the first 36 Zernike terms of the entire surface error were extracted for compensation. In the experiment, an additively-manufactured AlSi10Mg mirror with a diameter of 510 mm and a lightweight ratio of 86% was fabricated. To the best of our knowledge, an additively-manufactured mirror of such a diameter with such a high lightweight ratio has never been reported in the literature. Using the proposed on-machine measurement system, a repeatability of 50 nm root-mean-square (RMS) was achieved. Furthermore, comparative validation with coordinate measuring machine results confirmed the reliability of the on-machine measurement system. Subsequently, Zernike polynomials were employed to reconstruct the surface errors. After a single compensation cutting process, the surface error decreased from 0.636 µm to 0.30 µm (RMS), achieving a convergence rate of 52%. The experimental results demonstrate that the proposed on-machine measurement methodology, combined with an error compensation strategy, significantly improves both precision and efficiency of ultra-precision machining.

The wetting state is a fundamental property of a material surface, yet achieving precise control over this property remains a formidable challenge. Mastery of wetting behavior can impart tailored functionalities to surfaces, such as liquid repellency, anti-fouling, and directional liquid transport. Despite the potential benefits, strategies for rapid and reliable modulation of various wetting states have remained elusive until now. In this study, an innovative one-step laser-based strategy that enables precise and rapid manipulation of surface wetting states on carbon fiber reinforced plastic (CFRP) is presented. This approach allows for the creation of hydrophilic surfaces characterized by the Wenzel state, hydrophobic surfaces with a mixed Cassie-Baxter/Wenzel state, and robust superhydrophobic surfaces featuring a stable Cassie-Baxter state. The realization of a stable Cassie-Baxter state stems from the concurrent formation of hierarchical micro/nanostructures and the enrichment of low surface energy components. Critically, the resulting superhydrophobic CFRP surfaces with the Cassie-Baxter state exhibit exceptional stability, minimized adhesion, and superior anti-icing and de-icing properties. These findings provide both fundamental insights and a practical platform for the rapid development of non-wetting, multifunctional surfaces, significantly expanding the applicability of CFRP across diverse engineering domains.

Achieving high spatial uniformity in laser-induced periodic surface structures (LIPSS) has long remained elusive, as even femtosecond lasers, despite their nominally “cold” processing capability, cannot eliminate the stochastic defects that compromise long-range order. Here, we present a strategy that utilizes high-repetition-frequency nanosecond pulses, a regime traditionally deemed unsuitable for precision nano-patterning due to pronounced thermal dissipation, to fabricate one-dimensional (1D) LIPSS with uniform morphology on structurally homogeneous metallic glass (MG) substrates. This is achieved by exploiting strong inter-pulse correlation, which simultaneously moderates thermal fluctuations and sustains a coherent optical near-field to template deterministic pattern formation from stochastic seeds. Performing repeated scanning along the same single-line path transform these 1D patterns into regular two‑dimensional (2D) nanodot arrays. Finite-difference time-domain simulations reveal that a unified optical near-field interaction governs the entire structural evolution, from initial 1D ordering to subsequent 2D reconfiguration. The process preserves the MG substrate’s amorphous state and chemical composition while being inherently scalable.

Polycrystalline zinc selenide (p-ZnSe) is one of the most widely used infrared optical materials. Since p-ZnSe possesses soft and brittle properties, it is machined at micro/nanoscale for achieving ductile mode machining. In micro/nanoscale machining, the tool shape and edge sharpness have significant influence on tool-workpiece contact and mechanism of chip formation, and consequently affect the machined surface integrity. To reveal the effect of tool shape on the machined surface integrity of p-ZnSe, in this study, round-nose and spherical diamond tools, which have different tool geometries and edge radii, were used for machining p-ZnSe. Results present that the tool nose radius and edge radius are critical factors for the chip formation and phase transformation of the workpiece material. Increasing the edge radius or using spherical tool causes a burnishing effect without material removal. Local plastic deformation is caused by an intense compressive stress under a high effective negative rake angle. In addition, results show that no matter what kind of tool is used and how the material is deformed, grain boundary has a great influence on the machined surface integrity. This study provides an insight into the deformation mechanism of polycrystalline brittle material in nanoscale machining with respect to different tool shapes, which will guide improvement of machined surface integrity.

Random micro-structured surfaces (RSS) have great application potentials as various functional surface elements, such as optical diffusers and hydrophobic/hydrophilic surfaces. Conventional fabrication methods for RSS, such as chemical etching, are no longer suitable for modern requirements of high precision and controllability. In this study, a novel method was proposed for fabricating controllable random dimple arrays by using fast tool servo (FTS)-based single-point diamond turning. Firstly, small patches of quadratic surfaces were periodically arranged over a large surface area. Then the position, height, and size of each quadratic surface were adjusted by applying random values whose dynamic range is preset. In this way, the spatial difference between the dimples were under control within an adjustable range. Finally, the fabricated surface was evaluated to validate the effectiveness of the proposed method. Results showed that the machined surface feature matched precisely with the designed one. This method provides possibility for mass production of high-precision RSS by patterning mold inserts for molding/imprinting processes.

Tuning the surface wettability and adhesion of metallic glasses (MGs) is a promising approach to enrich their engineering applications. In this study, using nanosecond laser ablation in air, hierarchical micro/nanostructures were directly fabricated on a Zr-based MG surface. Following subsequent annealing, the surface exhibited superhydrophobicity (maximum contact angle: 166°, minimum sliding angle: 2°). Furthermore, the superhydrophobic surface could be tuned from low to high surface adhesion force by controlling the laser-ablated spot interval. By analyzing the laser-ablated structures and surface chemical compositions, the superhydrophobicity was related to the formation of hierarchical micro/nanostructures and the absorption of organic compounds with low surface free energy in air, and the change in surface adhesion force was attributed to the difference in surface roughness. The experimental results showed that the superhydrophobic surface with low adhesion force could be used in self-cleaning applications, while the superhydrophobic surfaces with different adhesion forces could be used in no-loss liquid transportation. This study provides an efficient and low-cost way to fabricate superhydrophobic MG surfaces with tunable adhesion, which will broaden the functional applications of MGs.

Laser bending forming, as a flexible and die-less forming approach, facilitates the three-dimensional shaping of sheets through the generation of thermal stress via laser-material interaction. In this study, the bending forming characteristics of CoCrFeMnNi high-entropy alloy sheets induced by nanosecond pulse laser irradiation were systematically investigated. The effects of parameters including laser power, scanning speed, number of scans, scanning interval, and sheet size on the bending angle, cross-sectional morphology, and hardness were studied in detail under both the laser single-line and multi-line scanning modes. The experimental results confirmed the effectiveness of nanosecond pulse laser irradiation for achieving accurate formation of CoCrFeMnNi sheets, with the successful fabrication of J, L, and U-shaped metal components. Apart from the forming ability, the cross-sectional hardness was significantly increased due to the grain refinement effect of nanosecond pulse laser irradiation. Furthermore, employing the laser single-line scanning mode enabled the effective rectification of overbending parts, showcasing complete recovery for small-angle overbending, and a remarkable 91% recovery for larger-angle overbending. This study provides an important basis for the bendability of CoCrFeMnNi sheets by laser forming and elucidates the evolution of the microstructure and mechanical properties in the bending region.

This study investigates the feasibility of using accelerometers for online monitoring in slow tool servo diamond turning (STSDT) of (111) CaF₂. Circumferential scratching tests were conducted under a two-factor, three-level design (spindle speeds: 30/45/60 rpm; depths of cut: 200/500/800 nm) with dry cutting. Acceleration was synchronously sampled at 12.8 kHz and quantified using RMS. Per revolution, the acceleration signal consistently exhibited three characteristic peaks that correspond to the well-known three-lobed surface pattern of (111) CaF₂. As depth of cut increased from 200 to 800 nm, peak amplitudes rose stepwise (≈0.013 g → 0.030 g → 0.035 g), while the effect of spindle speed was not significant. Converting the durations and intervals of the three peaks into brittle/ductile sector angles yielded good agreement with imaging measurements, with a mean error of 6.4%. Notably, the X-axis proved most sensitive to the brittle–ductile transition; this is hypothesized to arise from asymmetric loading on cleavage planes within the transition zone, inducing lateral micro-vibrations. Overall, accelerometer-based monitoring offers a low-cost, easily deployable, and real-time approach for identifying brittle–ductile states and guiding process control in CaF₂ STSDT.

Single-crystalline silicon, a key material in semiconductors and optical devices, is difficult to machine due to its high hardness and low fracture toughness, which lead to brittle fractures during ultra-precision cutting. Although single-crystalline diamond (SCD) tools are commonly used, their performance is limited by severe wear related to cleavage and anisotropic crystallographic properties. This study investigates the use of nano-polycrystalline diamond (NPD) tools to improve machining performance by suppressing crack propagation and homogenizing mechanical properties. The NPD tool, composed of nanoscale diamond grains, demonstrated more than twice the cutting life of SCD, and wear on their cutting edges progressed stably through abrasion induced by thermal accumulation, as evidenced by smooth worn areas and periodic grooves. In contrast to SCD, which were susceptible to impact loads, NPD achieved more stable surface quality by suppressing micro-pit formation owing to their high hardness and absence of cleavage behaviour. Therefore, the stable wear progression of NPD enables the Sz value to remain low (approximately 20–80 nm) for cutting distances below 15.7 km, indicating stable plastic deformation of the workpiece material and resulting in longer tool life and enhanced machining stability. This study highlights the advantages of NPD for long-distance ultra-precision cutting of silicon.

Amorphous silicon (a-Si) plays a crucial role in thin-film electronics, photovoltaics, and optoelectronics, where its surface structures significantly affect device performance. Ultrashort pulse lasers are ideal for modifying a-Si surfaces, but their surface integrity after irradiation are not clear. In this study, a non-ablative femtosecond laser irradiation method was developed to form nano-protuberances on the surface of a-Si without removing the material. The a-Si films (10 µm thick) were irradiated with a femtosecond laser (800 nm, 40 fs, 1 kHz) at energy densities of 0.03–0.15 J/cm². The influence of laser parameters on surface nano-protrusion formation and crystallization was investigated. Results indicate that laser energy density (Ed) govern the transition between nano-protrusions and nano-depressions: higher values (Ed '0.10 J/cm²) produce nano-depressions, while lower values (Ed '0.10 J/cm²) yield nano-protrusions. Raman spectroscopy confirms that the laser-induced nanostructures are accompanied by a phase transition from a-Si to crystalline silicon (c-Si). It is worth noting that these effects do not exist in monocrystalline silicon, indicating their wider applicability to amorphous materials. This patterning method based on femtosecond laser phase transition provides great potential for improving the performance of a-Si based devices in photovoltaic, optoelectronic, and optical anti-counterfeiting technologies.