Deformation and cracking caused by internal stress have been a long-standing challenge in the field of metal additive manufacturing. This paper presents a novel method for real-time stress assessment of laser-directed energy deposition (LDED) based on the shrinkage phenomenon of deposition layer – the Dynamic Contour Method (DCM). It integrates machine vision, three-dimensional reconstruction based on actual morphology, and numerical simulation to calculate rapidly stress development during the LDED process. Meanwhile, a mapping relationship between the surface shrinkage of the deposition layer and stress is established, providing a theoretical basis for the DCM. Regarding the validation of this method, the DCM simulations are compared with the experimentally calibrated thermo-mechanical coupling simulations. The results show a high degree of consistency, demonstrating the feasibility and accuracy of the DCM. This method provides a new digital twin framework for additive manufacturing.

Based on time-averaged digital holography, a vibration deformation measurement system was designed and a full process reconstruction and identification strategy was developed for detecting the micro-defects in optical materials. Through the double beam expansion setting and off-axis imaging adjustments, it is suitable for measuring optical materials with non-specular surfaces by double exposure shots. The scheme was applied to optical sandwich composites and 3D printed glass. Abnormal amplitudes occur at the defects due to different resonance frequencies, resulting in anomalous vibrations under excitation, and the differences in the amplitudes and phases before and after vibration can effectively characterize vibration amplitude and subsurface defects, proving that this method has a high detecting sensitivity.

To realize defect detection and locate the abnormal areas of optical components, we propose a high-sensitivity detection method based on the principle of digital holographic photoelasticity measurement. First, holograms are acquired before and after external force loading. Then, the complex amplitude is reconstructed, and the phase difference is calculated accordingly. Variables concerning birefringence are solved by obtaining multiple groups of holograms with different reference polarization directions and constructing a ratio function containing only the interference light intensity. Principal stress is calculated after external force loading. The proposed method can be applied to the detection of glass surface cracks, internal holes, and damage, and the reliability and performance of high-powered laser optical components can be guaranteed.

Label-free imaging of transparent biological cells is essential for studying native morphology and dynamics without the interference of chemical stains or phototoxic effects. Existing phase contrast methods, however, often rely on computational post-processing, complex optical setups, or mechanical adjustments. In this paper, we propose a real-time, label-free phase contrast imaging method by integrating a programmable spatial light modulator (SLM) into a conventional off-axis digital holographic microscopy (DHM) system. The method introduces a digitally synthesized phase mask at the Fourier plane to modulate the low-frequency spectrum of the object wave, thereby enhancing image contrast directly in the reconstructed intensity. A spectrum-based calibration procedure is employed to ensure accurate mask alignment. Experimental validation on SK-MEL-28 and MCF-7 cell samples further confirms the method's effectiveness. The experimental results demonstrate significant improvement in image clarity across brightfield acquisition, hologram formation, reconstructed intensity and phase images.

Sensing an incoming acoustic signal is typically associated with absorbing the energy, perturbing the measurement and therefore causing a deformation of the sensing elements, which is mainly related to the acoustic wave pressure. Here, we demonstrated a fiber-tip based Fabry-Perot (FP) acoustic probe sensor, which was directly printed on an optical fiber tip by a two-photon 3D printing technique and assembled by a glass horn structure, which can improve the sensitivity. It showed that the sensor has a-3 dB bandwidth of 366.05 kHz at the first resonant frequency of 467.84 kHz. A low noise-limited minimum detectable pressure level of 4.71 mPa/ Hz1/2@100 kHz is obtained. Due to the acoustic wave focusing property of the horn structure, the detected signal intensity can be amplified by 4 times as the sensor located at the bottom position. It demonstrates that 3D printed micro acoustic devices could be used for weak acoustic wave detection in the applications of partial discharge, photoacoustic imaging and non-destructive detection.

Digital holography has transformative potential for the measurement of stacked-chip microstructures due to its non-invasive, single-shot, full-field characteristics. However, significant light scattering and diffraction at steep edges in step microstructures cause the batwing effect, leading to measurement errors. Herein, we propose a standard-deviation-based adaptive median filter to eliminate batwing effects in step microstructure measurement using digital holography. The standard deviation determines the positions of the steps and the range of the batwing effect. During filtering, the filter window size varies: it adjusts according to the center’s position within the batwing effect range and reduces outside this range to prevent distortion in other regions. Filtering weights are set to maintain information integrity while using larger filter windows. Experiments on the Standard Resolution Target USAF 1951 and the standard step height target show that our method successfully eliminates batwings while preserving the integrity of the remaining profile.

Two-photon photodynamic therapy (TP-PDT), which utilizes near-infrared light to excite photosensitizer via two-photon excitation (TPE), is a promising modality in the treatment of deeply seated tumors or thick tumors. However, the TPE domain is much smaller than the tumor volume, significantly limiting the therapeutical outcomes of TP-PDT. Here, a light-sheet TPE system is designed and constructed using a cylindrical lens for highly efficient TP-PDT. The light-sheet TPE performance is characterized and optimized via theoretical analysis and experimental studies in solution, phantom, and tumor. The optimized excitation system can reach a large TPE domain of 2.6 x 2.7 x 0.09 mm in the tumor, which is not achievable using conventional TPE methods, enabling TPE and subsequently generated reactive oxygen species to cover the whole tumor under line-scanning. Outstanding TP-PDT therapeutic performance of 70% tumor growth inhibition rate is achieved under line-scanned light-sheet TPE, making the proposed light-sheet excited TP-PDT a potential therapeutic tool for future translational research. A simple light-sheet two-photon excitation system using a cylindrical lens for femtosecond laser shaping achieves a significantly expanded two-photon excitation domain of 2.6 x 2.7 x 0.09 mm. Through simple 1D scanning, the light-sheet excited two-photon phtodynamic therapy achieves about 70% tumor growth inhibition rate in vivo. image

A well-established method for 3D nanoparticle tracking is the double-helix point spread function (DH-PSF) engineering, which uses additional optical elements to make the PSF exhibit different rotation angles with varying depths of nanoparticles. Splicing the symmetric spiral phases together using the phase splicing method can generate the modulated phase mask of 2 pi-DH-PSF. The 2 pi-DH-PSF has a linear rotation rate at each axial position and has a larger rotation angle, showing a more accurate rotation angle and depth translation. Experiments with a phase-only spatial light modulator demonstrate the potential of the 2 pi-DH-PSF. Finally, we successfully conducted 3D nanoparticle tracking experiments at 8-mu m depth with a numerical aperture of 1.4, showing its great potential.

Single-atom dispersed catalysts (SACs) have gained considerable attention in organic contaminants remediation due to their superior reactivity and stability. However, the complex and costly synthesis processes limit their practical applications in environmental protection. Herein, a facile and cost-effective single-atom iron catalyst (Fe-SA/NC) anchored on nitrogen-doped porous carbon was first fabricated by using waste biomass as a carbon source. The Fe-SA/NC catalyst exhibited outstanding performance with a high turnover frequency of 1.72 min-1 toward antibiotics degradation via peroxymonosulfate activation. ECOSAR program and algae growth experiments demonstrated that the byproducts produced during the sulfamethoxazole degradation process were not detrimental to the aquatic environment. Radical quenching and electron paramagnetic resonance experiments revealed that Fe-SA/NC remarkably promoted 1O2 production in PMS-assisted reaction, and thus 1O2 contributed as much as 78.77% to sulfamethoxazole degradation. As indicated by experiment and density functional theory (DFT) calculations, FeN2O2 configuration serves as the active site. DFT calculations further presented the most rational generation route of 1O2 as PMS→OH* →O* →1O2. We also designed Fe-SA/NC embedded spherical pellets for contaminants elimination at the device level. This study offers new insights into the synthesis of SACs from waste biomass and their practical application in environmental remediation.

With the rapid and continuous development of nanomanufacturing technology, the demands for both large range and high precision metrology of structured surfaces are becoming increasingly urgent. This paper proposes a metrological measurement system based on a commercial atomic force microscope. By using the nano-positioning platform from SIOS, the measurement range of the system expands from 110 μm × 110 μm × 20 μm to 25 mm × 25 mm × 5 mm. A signal amplifier with low noise and a high common mode rejection ratio that decreases the noise level of the measurement system to 2 nm is designed. Integration of the metrological system, signal processing, and calibration of the whole system is introduced. Three experimental studies are carried out on an ultrahigh step, an atomic deposition grating, and a cutting tool. The experimental results demonstrate high measurement repeatability and reproducibility in both vertical and lateral directions. By repeating 10 times of measurement, the expended uncertainties of the step and the grating measurement are 36.24 nm and 0.60 nm, respectively. Additionally, measurement of a cutting tool tip is conducted to illustrate the performance of the system. The Ra and Rz values of the tool tip arc ripple are 29.8 nm and 189 nm, respectively.

This study is concerned with the security of networked systems with random sampling intervals and deception attacks using non-fragile sampled-data control. We first establish a discrete-time stochastic model framework for the networked system with random sampling intervals and deception attacks. Subsequently, by the vectorization and Kronecker product operation, a non-fragile controller is designed such that the exponential mean-square stability of resulting discrete-time stochastic system is guaranteed. Finally, a numerical example is presented to show the effectiveness of the designed algorithm.

Single-phase face-centered cubic (fcc) medium-entropy alloys (MEAs) generally exhibit good ductility but insufficient room temperature strength that limits their potential application. Here, a deformation mechanism of twin-induced transformation was achieved to strength the CoCrNi-base alloy with gradient nanostructure obtained by surface mechanical rolling treatment (SMRT) technique. Significantly, the SMRT processed CoCrNi-based alloy exhibits a substantial improvement in the mechanical property comparing with the wrought counterpart by increasing the yield strength from 964 to 1664 MPa and the ultimate tensile strength from 1210 to 1883 MPa, while maintaining a uniform elongation of 11.3%. The enhanced combination of strength and ductility attributes to the extra hardening from the synergistic effect of nanostructure and phase transformation.

Optical fiber microresonators have attracted considerable interest for acoustic detection because of their compact size and high optical quality. Here, we have proposed, designed, and fabricated a spring-based Fabry–Pérot cavity microresonator for highly sensitive acoustic detection. We observed two resonator vibration modes: one relating to the spring vibration state and the other determined by the point-clamped circular plate vibration mode. We found that the vibration modes can be coupled and optimized by changing the structure size. The proposed resonator is directly 3D printed on an optical fiber tip through two-photon polymerization and is used for acoustic detection and imaging. The experiments show that the device exhibits a high sensitivity and low noise equivalent acoustic signal level of 2.39 mPa/Hz1/2 at 75 kHz that can detect weak acoustic waves, which can be used for underwater object imaging. The results demonstrate that the proposed work has great potential in acoustic detection and biomedical imaging applications.

Digital holography has transformative potential in measuring stacked-chip microstructures due to its noninvasive, single-shot, full-field characteristics. However, uncertainties in reconstruction distance inevitably lead to resolving blur and reconstruction distortion. Herein, we propose a phase-based reconstruction optimization method that consists of a phase-evaluation function and a structured surface-characterization model. Our proposed method involves setting a reconstruction distance range, obtaining phase information using sliced numerical reconstruction, and optimizing the reconstruction distance by finding the extreme value of the function, which identifies the focal plane of the reconstructed image. The structure of the surface topography is then characterized using the characterization model. We perform simulations of the recording, reconstruction, and characterization to verify the effectiveness of the proposed method. To further demonstrate the approach, a simple holographic recording system is constructed to measure a standard resolution target, and the measurement results are compared with a commercial instrument. The simulation and experiment demonstrate, respectively, 31.16% and 34.41% improvement in step-height characterization accuracy.

In recent years, two-dimensional layered material MXene has attracted extensive attention in the fields of sensors due to its large specific surface area and rich active sites. So, we employed multilayer Ti3C2TX and SnO2 microspheres to prepare SnO2/MXene composites for enhancing gas-sensing properties of pristine SnO2. The composite was brushed on a microelectromechanical system (MEMS) platform to make resistance-type gas sensors with low power consumption. The gas-sensing results show that the SnO2/MXene sensor with the best composite ratio (SnO2: MXene mass ratio is 5:1, named SM-5) greatly improves gas sensitivity of SnO2 sensor, among which the sensitivity to ethanol gas is the highest. At the same time, the composite also speeds up the response recovery speed of the sensor. When the SM-5 sensor worked at its optimal temperature 230 °C, its response value to 10 ppm ethanol reaches 5.0, which is twice that of the pristine SnO2 sensor. Its response and recovery time are only 14 s and 26 s, respectively. The sensing mechanism of the composite is discussed according to the classical the space charge or depletion layer model. It is concluded that the Schottky barrier of composites and the metal properties of Ti3C2Tx are responsible for improvement of the gas-sensing properties of the composite.

We propose to reconstruct 3D images by combining the merits of transport of intensity and digital holography. The proposed method solves the transport-of-intensity equation by using digital holographic reconstructed images as inputs. Our simulation and experimental results show that this method can eliminate quadratic phase aberration introduced by the microscope objective in digital holographic microscopy. This proposed phase retrieval method is free of phase unwrapping process. It is thus efficient in removing quadratic phase aberration introduced by the microscope objective.

This paper proposes a high-precision characterization method for step height of micro-structured surfaces based on the K-means algorithm. First, the original measured surface data obtained by the three-dimensional surface measuring instrument is dimensionally reconstructed. Secondly, use the K-means-based clustering algorithm and data mapping to identify and remove outliers, and the centroid distance of the reconstructed data in the three-dimensional space is mapped to the required step height value. Finally, through the iterative convergence design, the accuracy and robustness of the algorithm characterization results are further improved. Experiment on simulated data shows that this method is robust against outliers. It can effectively and accurately characterize step heights for measurement data of big size. Also, the method can simultaneously ignore outliers during parameterization.

Quantitative characterization and uncertainty evaluation of areal step height are of increasing importance for semiconductor manufacturing. However, step characterizations often confront problems of repeatability and reproducibility due to fitting of upper and lower planes. To solve this problem, we propose a cluster-based method for step height characterization and uncertainty evaluation. By data reconstruction and $K$ -means clustering, our method converts characterizing steps into approximating Euclidean distances, without necessity to fit planes. Moreover, it can evaluate uncertainties simultaneously with parameterization. The proposed method is first validated with synthetic data. Then, two experiments, respectively, on nominal 5 $\mu \text{m}$ and 90 nm standard artifacts are carried out. The characterization results highly conform to the calibrated values, with 0.0986% and 1.22% differences, respectively. Comparing to the latest ISO method, the cluster-based method presents better performance on repeatability and reproducibility. The experimental results demonstrate that the method works well for measurement either with or without outliers.

This article proposes a frequency-dependent adaptive noise cancellation-based tracking controller for the trajectories’ stabilization of a flexible rotor supported on full lubricated journal bearings. The aim is to provide a general solution to the control problem by introducing a modular and closed-form formulation. Starting from the medialization of the journal bearings nonlinear fluid film forces acting on the rotor during the motion, a manual matrix solution of equations is achieved. The formulation takes in account the journal bearing lubricating problem in terms of both cavitated and uncavitated short bearing analytical solutions. The adaptive vibration-reducing tracking controller is based on a quick online estimation of the mutual forces acting on the rotor, in the presence of the imposed frequency disturbances, under the assumption of a known exosystem dynamics. The controller acts as a force observer and modal disturbance estimator. Then, it is independent of the operating conditions of the bearings. A mathematical proof and numerical simulations are provided to validate the proposed control. The control response results very fast.

Objective Photodynamic therapy (PDT), which canablate cancer cells or diseased tissue by the generated reactive oxygen species (ROS) once the photosensitizers (PSs) are excited by light with specific wavelength, has attracted various attention in the last decades due to its unique advantages, including non-invasiveness, few side-effects, etc. The advancement of PDT has been significantly restricted by the penetration depth of the excitation light and sub-cellular organelles targeting capability. Here, an effective carbon dots (C-dots) photosensitizer with intrinsic nucleolus targeting capability is synthesized, characterized, and employed for in vitro photodynamic anticancer therapy with enhanced treatment performance at a low dose of PS and light irradiation. Methods The optical system, which included a microscope and femtosecond laser, was designed for two-photon phototherapy. The nucleolus-targeted C-dots were synthesized using microwave heating. The characteristics of synthesized C-dots including particles size, absorption and emission, two-photon fluorescence, photobleaching, biocompatibility, etc., were measured by DLS measurement, UV-Visible spectrophotometer, fluorescence spectrometer, femtosecond laser, CCK-8 kit, respectively. The nucleolus-targeting capability of C-dots was investigated using fluorescence imaging. The HeLa cells were incubated with C-dots and irradiated with a femtosecond laser before cell viability was examined using Calcein-AWPI staining and fluorescence imaging. Results and Discussions The microwave heating method selects citric acid and ethylenediamine as raw materials to synthesize the C-dots. The synthesized C-dots were studied using dynamic light scattering measurement, and the average size of the C-dots was approximately 1 nm [Fig. 2 (a)]. The C-dots absorbed light in various wavelengths from 300 to 700 nm, with the main absorption peak at 360 nm and a shoulder peak at 450 nm [Fig. 2 (b)]. The C-dots exhibited excitation-dependent emission [Fig. 2 (c)] and significant two-photon fluorescence when exposed to femtosecond laser irradiation [Fig. 2(d)]. The ROS-generation capability of the C-dots in aqueous solutions was investigated using ABDA as the ROS indicator under white light irradiation (400-700 nm, 100 mW/cm(2)). The ABDA was almost decomposed after 10 min illumination [Fig. 2 (e), indicating the ROS-generation capability of the C-dots. The long-term stability and photostability of the C-dots were characterized by measuring the absorption spectra at different time points [Fig. 2 (f)] and after continuous irradiation [Fig. 2 (g), respectively. The experimental results showed that the C-dots had good long-term stability and photostability. CCK-8 kits were used to evaluate the biocompatibility of the C-dots before undergoing in vitro photodynamic therapy. For 24 and 48 h, no significant difference existed between control cells and cells treated with the C-dots in the mass concentration range of 250-750 g/mL, indicating the excellent biocompatibility of the C-dots. The C-dots were treated with HeLa cells to investigate their intracellular position, followed by fluorescence imaging. The fluorescence signal of the C-dots was observed in some round areas, i.e., nucleoli. HeLa cells were co stained with the C-dots and one commercial nucleolus imaging probe, SYTO RNASelect, to demonstrate the C-dots' nucleolus-targeting capacity. Figure 3 showed the fluorescence of the C-dots completely overlapped with that of SYTO RNASelect, confirming that the C-dots could specifically stain the nucleolus. HeLa cells were cultured with/without the C-dots (500 g/mL) for 3 h before being exposed to femtosecond laser irradiation to study the two-photon PDT efficiency of the C-dots (740 nm, 28 mW). The treated cells were incubated for 4 h following the irradiation and stained with Calcein-AM and PI. Figure 4 showed that more cells were PI-positive with an increment of irradiation time. When the irradiation time reached 45 s, almost all cells were necrotic, suggesting the excellent cancer cell ablation potential of nucleolus-targeted two-photon photodynamic treatment. The identical irradiation did not result in necrosis in the absence of the C-dots, indicating that laser irradiation had no effect. Conclusions We designed and synthesized novel C-dots with intrinsic nucleolus-targeting and ROS-generation capabilities. The nucleolus-targeted two-photon PDT exhibits outstanding cancer cell ablation efficiency at a low dose of the C-dots and light irradiation because the C-dots generated ROS is positioned within the nucleolus, which is an efficient cancer therapy site. Additionally, the developed C-dots possess some unique advantages, including ultrasmall size, long-term stability, and excellent biocompatibility, making them promising for practical two-photon PDT applications.