Laser interference lithography (LIL) is an established technique for fabricating precise and periodic microstructures. The non-orthogonal Lloyd’s mirror interferometer, a type of wavefront division interferometer with a simple structure and short non-common optical paths, offers excellent stability even in ordinary laboratory environments. Additional advantages include facile adjustment of the pitch of the interference fringe without a photomask, and the generation of large-area microstructures in a single step. However, the achievable geometries of the interference pattern are fundamentally limited by the design of the interference field, and the optical configurations or optical parameters must be redesigned to generate different patterns. To address this issue, a novel non-orthogonal two-axis Lloyd’s mirror interferometer employing active wavefront control using a spatial light modulator is proposed herein. The fringe position of the two-axis interference fringe pattern (dot array fringes) is controlled by independently applying dynamic phase modulation to the exposure sub-beams, enabling arbitrary translation of the fringe patterns during exposure. By shifting the positions of the dot array fringes, various micropattern geometries can be fabricated without modifying the optical configuration or optical parameters, while maintaining the advantages of LIL. Numerical calculations demonstrated that the dot array fringes can be translated independently in the X- and Y-directions via phase modulation, where an exposure-dose pattern with non-elliptical arbitrary patterns was generated by controlling the fringe trajectory. Using a constructed prototype optical system, various microstructures were fabricated by controlling the fringe trajectory and were quantitatively evaluated using scanning electron microscopy and atomic force microscopy. The fabricated geometrical parameters showed fair agreement with the corresponding simulated results, confirming the feasibility of the proposed method.
For conventional laser Fizeau phase-shifting interferometry, form measurement of ellipsoidal binary gratings remains challenging because of the discontinuous grating structure with groove depths exceeding half the illumination wavelength. In this study, we propose a spatio-temporal Fourier analysis method that extends conventional laser Fizeau interferometry for full-field form measurement of ellipsoidal binary gratings. By applying a three-dimensional Fourier transform to phase-shifted interferograms, combined with spatial low-pass filtering, the low-spatial-frequency phase is extracted. Moreover, the background intensity is utilized for segmentation masks, enabling independent segmentation and reconstruction of the upper and lower grating surfaces. Simulations show that the residual reconstruction errors remain below 6.5 nm root-mean-square for a groove depth of 2.65 μm. Experimental validation using a 30 mm flat grating agrees well with state-of-the-art point-scanning optical profilometric measurements, where a 300 mm ellipsoidal grating was successfully characterized. The proposed method extends conventional Fizeau interferometry to enable accurate full-field surface form metrology of ellipsoidal binary gratings.
Electropolishing (EP) is a key enabling technique used to fabricate ultrasmooth surfaces in inertial confinement fusion (ICF) targets. However, the coupled effects of material removal, thermal fields, and surface morphology on dimensional stability and laser-driven performance remain poorly understood. This study investigates the EP of copper targets in a phosphoric acid–glycerol electrolyte via experiments, COMSOL Multiphysics simulations, and FLASH radiation–hydrodynamics modeling. The results reveal that thin foils are highly susceptible to warping due to the interplay of nonuniform material dissolution, the edge-enhanced current density, and thermally induced stress gradients. A stable diffusion-controlled polishing regime is identified, under which surface asperities are preferentially removed, resulting in a reduction in roughness from 48 nm to 5 nm at 55 °C, a 3:1 acid-rich electrolyte, and 1.2 V. More importantly, a cross-scale correlation between surface morphology and laser ablation behavior is established. FLASH simulations demonstrate that increasing surface roughness amplifies lateral nonuniformities in electron temperature and density fields, thereby accelerating the growth of Rayleigh–Taylor (RT) instability. In contrast, nanoscale-smooth surfaces exhibit ablation characteristics comparable to an ideal interface, with significantly suppressed perturbation growth. These findings establish a mechanistic link between EP-induced surface evolution and laser-driven stability, offering a framework for optimizing surface and ablation performance.
The performance of gallium oxide (Ga2O3) is critically dependent on substrate surface quality, while chemical mechanical polishing (CMP) plays a key role in achieving high-quality finishing of single-crystal Ga2O3. However, material removal mechanisms under varying chemical environments remain unclear, thus hampering further optimization. This study investigated the material removal behavior of u03B2-Ga2O3 using a tribological approach. Tribochemical interactions between u03B2-Ga2O3 and various chemical solutions (deionized water [H2O], 1% hydrogen peroxide [H2O2], and 3% H2O2) using different counterbodies (aluminum oxide [Al2O3], zirconium dioxide [ZrO2], and silicon nitride [Si3N4]) were systematically analyzed. The results demonstrated a pronounced dependence of tribological behavior on the oxidative aqueous environment. Combined with surface morphology and chemical component analysis, H2O2 induced anisotropic selective etching and enhanced surface hydroxylation, leading to an elevated coefficient of friction and wear rate (increasing from ~ 9.74 u00D7 10-8 mm3/(Nu00B7m) in water to ~ 2.27 u00D7 10u22126 mm3/(Nu00B7m) in 3% H2O2). Furthermore, the tribological performance was governed by the counterbody material. Whereas amphoteric ZrO2 exhibited mild wear behavior similar to that of Al2O3, Si3N4 triggered severe mechanical interactions, resulting in the highest wear rate (~ 5.28 u00D7 10u22126 mm3/(Nu00B7m)). Cross-sectional microstructural characterization revealed that this interaction leads to the formation of a distinct structural damage gradient in the subsurface. This study provides fundamental insights into the tribochemistry of u03B2-Ga2O3, and these findings are anticipated to offer valuable guidance for the future optimization of CMP processes.
Deep rolling and machine hammer peening are widely applied mechanical surface treatments for improving the fatigue performance of high-strength materials by introducing compressive residual stresses and modifying the near-surface material state. Despite their industrial relevance, the effect of strain rate on material surface modification remains insufficiently understood, especially regarding its interaction with load-controlled deformation and depth-dependent material response. In this study, the effect of strain rate on the surface modification of AISI 4140 steel is investigated using explicit finite element simulations with a strain rate-sensitive constitutive model, supported by experimental residual stress validation. The depth-resolved quantification of plastic strain rate fields enables the continuous and impact-based loading modes in deep rolling and machine hammer peening to be compared within a consistent framework. The evolution of internal material loads and plastic strain rate fields is quantitatively analyzed under quasi-static conditions. A dedicated spatial-averaging framework is employed to extract numerically stable and physically representative plastic strain rate depth profiles beneath the treated surface, enabling the consistent quantification of maximum strain rates and the effective penetration depth. Results show distinct strain rate characteristics for each process. In machine hammer peening, the strain rate appears as transient, highly localized peaks governed by impact velocity–contact time coupling. Thus, the strain rate cannot be independently varied, limiting its suitability for isolated analysis. Therefore, deep rolling is used to assess the influence of strain rate on material surface modification. Under constant normal load, the rolling speed is varied to adjust the maximum plastic strain rate while preserving comparable contact mechanics. Maximum plastic strain rates of 101–103 s−1 are observed in the near-surface region. Depth-resolved analyses reveal that the strain rate primarily affects the accumulation and localization of plastic deformation in the near-surface and shallow subsurface layers, whereas its influence rapidly diminishes with increasing depth. The magnitude and penetration depth of compressive residual stresses are primarily governed by machining parameters such as applied load and tool geometry, while the strain rate acts as a process variable that influences the material response rather than directly controlling the residual stress state.
