Power Enhancement and Spot Homogenization Design for Arrayed Semiconductor Lasers.

Improving the spot brightness and uniformity of arrangement of the array laser is conducive to ensuring the beam quality of the fiber laser. Based on the light tracing principle, the optical model performance of two common fiber lasers was first analyzed. Then, a novel rotationally polarized optical model with high power and spot uniformity was designed and optimized on the basis of the aforementioned analysis. The results of the evaluation metrics of the multi-indicator optical model show that the spot uniformity of our proposed model improved by 24.03%, the power improved by 0.55%, and the maximum light distance was shortened from 120 mm to 82.58 mm. Further, the results of the coupling tolerance analysis of the optical elements show that the total coupling efficiency was 89.04%. The coupling power and tolerance relationships did not produce degradation compared with the traditional model. Extensive comparative results show that the designed rotationally polarized optical path model can effectively improve the optical coupling efficiency and spot uniformity of arrayed semiconductor lasers.

Hierarchical attention-guided multiscale aggregation network for infrared small target detection.

All man-made flying objects in the sky, ships in the ocean can be regarded as small infrared targets, and the method of tracking them has been received widespread attention in recent years. In search of a further efficient method for infrared small target recognition, we propose a hierarchical attention-guided multiscale aggregation network (HAMANet) in this thesis. The proposed HAMANet mainly consists of a compound guide multilayer perceptron (CG-MLP) block embedded in the backbone net, a spatial-interactive attention module (SiAM), a pixel-interactive attention module (PiAM) and a contextual fusion module (CFM). The CG-MLP marked the width-axis, height-axis, and channel-axis, which can result in a better segmentation effect while reducing computational complexity. SiAM improves global semantic information exchange by increasing the connections between different channels, while PiAM changes the extraction of local key information features by enhancing information exchange at the pixel level. CFM fuses low-level positional information and high-level channel information of the target through coding to improve network stability and target feature utilization. Compared with other state-of-the-art methods on public infrared small target datasets, the results show that our proposed HAMANet has high detection accuracy and a low false-alarm rate.

Laser-Textured Hybrid Brass Pattern Array Surface for High-Efficiency Fog Collection.

Fog collection holds promise for addressing water shortage. However, the conventional fabrication of fog collection devices, normally chemical methods, suffers many challenges, such as complicated preparation and environmental issues. Herein, we proposed a green fabrication strategy to construct superhydrophobic/hydrophilic surfaces on the brass substrate via the combination of laser fabrication and heat treatment. The wettability of brass is directly dictated by the laser process parameters. The different superhydrophobic/hydrophilic hybrid pattern surface with a rectangular/triangular array was designed for an optimal fog collection performance. The maximum water collection efficiency of the prepared surface is measured up to 427.36 mg h-1 cm-2, which is 97% higher than that of the control sample. Furthermore, the surface can be folded into different forms to realize a flexible collector. We envision that our work provides a green fabrication strategy to construct a superwetting surface for highly efficient fog collection.

Optimization of Coupling Efficiency in Butterfly Optical Communication Laser Based on Chaotic Adaptive Seeker Optimization Algorithm.

A chaotic adaptive seeker optimization algorithm (CASOA) is proposed in this study to improve the coupling efficiency and accuracy of a butterfly optical communication laser. It primarily relies on chaotic disturbance to improve seeker search performance. The chaotic disturbance enables the algorithm to jump out from local extremes. Furthermore, chaos is associated with a novel strategy for optimizing search paths with a small population. A simulation and experiment are conducted to demonstrate that the CASOA with a few seekers has an excellent search success rate with few iterations in the coupling alignment. These results indicate that the proposed CASOA can reliably improve the coupling accuracy and efficiency of laser diodes and single-mode fibers.

Observation of optical anisotropy and a linear dichroism transition in layered silicon phosphide.

The investigation of in-plane two-dimensional (2D) anisotropic materials has garnered significant attention due to their exceptional electronic, optical, and mechanical characteristics. The anisotropic optical properties and angle-dependent photodetectors based on 2D anisotropic materials have been extensively studied. However, novel in-plane anisotropic materials still need to be explored to satisfy for distinct environments and devices. Here, we report the remarkable anisotropic behavior of excitons and demonstrate a unique linear-dichroism transition of absorption between ultraviolet and visible light in layered silicon phosphide (SiP) through the analysis of polarization photoluminescence (PL) and absorbance spectra. Its high absorption linear dichroism ratio of 1.16 at 388 nm, 1.15 at 532 nm, and 1.19 at 733 nm is revealed, suggesting the brilliant non-isotropic responses. The robust periodic variation of the A1 and A2 Raman modes in 2D SiP materials allows for the determination of their crystal orientation. Furthermore, the presence of indirect excitons with phonon sidebands in the temperature-dependent PL spectra exhibits non-monotonic energy shifts with increasing temperature, which is attributed to an enhanced electron-phonon interaction and thermal expansion. Our findings provide valuable insights into the fundamental physical properties of layered SiP and offer guidelines for designing polarization-sensitive photodetectors and angle-dependent devices based on 2D anisotropic materials.

Bioinspired Near-Full Transmittance MgF2 Window for Infrared Detection in Extremely Complex Environments.

Due to the extreme complexity of the anti-reflective subwavelength structure (ASS) parameters and the drastic limitation of Gaussian beam manufacturing accuracy, it remains a great challenge to manufacture ASS with ultrahigh transmittance on the surface of infrared window materials (such as magnesium fluoride (MgF2)) directly by femtosecond laser. Here, a design, manufacturing, and characterization method that can produce an ultrahigh-performance infrared window by femtosecond laser Bessel beam is proposed. Inspired by the excellent anti-reflective and hydrophobic properties of the special structure of dragonfly wings, a similar structural pattern with grid-distributed truncated cones is designed and optimized for its corresponding parameters to achieve near-full transmittance. The desired submicron structures are successfully fabricated by a Bessel beam after effectively shaping the beam. As a practical application, the bioinspired ASS is manufactured on the surface of MgF2, achieving an ultrahigh transmittance of 99.896% in the broadband of 3-5 µm, ultrawide angle of incidence (over 70% at 75° incidence), and good hydrophobicity with a water contact angle of 99.805°. Results from infrared thermal imaging experiments show that the ultrahigh-transmittance MgF2 window has superior image acquisition and anti-interference performance (3.9-8.6% image contrast enhancement and more accurate image edge recognition) in an environment with multiple interfering factors, which may play a significant role in facilitating applications of infrared thermal imaging technologies in extremely complex environments.

Strain-tunable valley polarization and localized excitons in monolayer WSe2.

Monolayer transition metal dichalcogenides (TMDs) have a crystalline structure with broken spatial inversion symmetry, making them promising candidates for valleytronic applications. However, the degree of valley polarization is usually not high due to the presence of intervalley scattering. Here, we use the nanoindentation technique to fabricate strained structures of WSe2 on Au arrays, thus demonstrating the generation and detection of strained localized excitons in monolayer WSe2. Enhanced emission of strain-localized excitons was observed as two sharp photoluminescence (PL) peaks measured using low-temperature PL spectroscopy. We attribute these emerging sharp peaks to excitons trapped in potential wells formed by local strains. Furthermore, the valley polarization of monolayer WSe2 is modulated by a magnetic field, and the valley polarization of strained localized excitons is increased, with a high value of up to approximately 79.6%. Our results show that tunable valley polarization and localized excitons can be realized in WSe2 monolayers, which may be useful for valleytronic applications.

One Droplet toward Efficient Alcohol Detection Using Femtosecond Laser Textured Micro/Nanostructured Surface with Superwettability.

Alcohol with different concentrations is commonly used in food, industry, and medicine fields all over the world. However, current methods for detecting alcohol concentration are restricted to large sample consumption, additional senergy consuming, or complex operations. Here, inspired by superwettability of lotus leaves, a superhydrophobic and superorganophilic surface is designed on the polydimethylsiloxane (PDMS) for one droplet efficient alcohol detection, which is prepared via femtosecond laser direct writing technology. Meanwhile, the contact angles of droplets with various alcohol concentrations on the laser-treated PDMS (LTP) surface are different. Based on the above characteristic, alcohol concentration through contact angle measurement without any external energy is directly detected, which is simple and efficient. Furthermore, it is worth noting that the LTP surface remains stable wettability after 1000 water-ethanol cycles and 300 days tests in air, indicating strong surface repeatability and stability. Significantly, the LTP surface has a broad potential application in one droplet detecting alcohol concentration, fake or genuine wine, and alcohol molecules. This work provides a new strategy to fabricate a superwetting surface for efficient one droplet alcohol detection.

Moiré Enhanced Potentials in Twisted Transition Metal Dichalcogenide Trilayers Homostructures.

The exploration of moiré superlatticesholds promising potential to uncover novel quantum phenomena emerging from the interplay of atomic structure and electronic correlation . However, the impact of the moiré potential modulation on the number of twisted layers has yet to be experimentally explored. Here, this work synthesizes a twisted WSe2 homotrilayer using a dry-transfer method and investigates the enhancement of the moiré potential with increasing number of twisted layers. The results of the study reveal the presence of multiple exciton resonances with positive or negative circularly polarized emission in the WSe2 homostructure with small twist angles, which are attributed to the excitonic ground and excited states confined to the moiré potential. The distinct g-factor observed in the magneto-optical spectroscopy is also shown to be a result of the confinement of the exciton in the moiré potential. The moiré potential depths of the twisted bilayer and trilayer homostructures are found to be 111 and 212 meV, respectively, an increase of 91% from the bilayer structure. These findings demonstrate that the depth of the moiré potential can be manipulated by adjusting the number of stacked layers, providing a promising avenue for exploration into highly correlated quantum phenomena.

A broad range and piezoresistive flexible pressure sensor based on carbon nanotube network dip-coated porous elastomer sponge.

Flexible pressure sensors have provided an attractive option for potential applications in wearable fields like human motion monitoring or human-machine interfaces. For the development of flexible pressure sensors, achieving high performance or multifunctions are popular research tendencies in recent years, such as improving their sensitivity, working range, or stability. Sponge materials with porous structures have been demonstrated that they are one of the potential substrates for developing novel and excellent flexible pressure sensors. However, for sponge-based pressure sensors, it is still a great challenge to realize a wide range of pressures from Pa level to hundreds kPa level. And how to achieve mechanical robustness remains unsolved. Here, we develop a flexible pressure sensor based on multicarbon nanotubes (MWCNTs) network-coated porous elastomer sponge with a broad range and robust features for use in wearable applications. Specifically, polyurethane (PU) sponge is used as the substrate matrix while dip-coated PU/MWCNTs composites as a conductive layer, achieving a highly bonding effect between the substrate and the conductive material, hence a great mechanical robust advantage is obtained and the working range also is improved. The pressure sensor show range of up to 350 kPa, while the minimum detection threshold is as low as 150 Pa. And before and after rolling by a bicycle or electric motorcycle, the sensor has the almost same responses, exhibiting great robustness.

Wetting Ridge-Guided Directional Water Self-Transport.

Directional water self-transport plays a crucial role in diverse applications such as biosensing and water harvesting. Despite extensive progress, current strategies for directional water self-transport are restricted to a short self-driving distance, single function, and complicated fabrication methods. Here, a lubricant-infused heterogeneous superwettability surface (LIHSS) for directional water self-transport is proposed on polyimide (PI) film through femtosecond laser direct writing and lubricant infusion. By tuning the parameters of the femtosecond laser, the wettability of PI film can be transformed into superhydrophobic or superhydrophilic. After trapping water droplets on the superhydrophilic surface and depositing excess lubricant, the asymmetrical wetting ridge drives water droplets by an attractive capillary force on the LIHSS. Notably, the maximum droplet self-driving distance can approach ≈3 mm, which is nearly twice as long as the previously reported strategies for direction water self-transport. Significantly, it is demonstrated that this strategy makes it possible to achieve water self-transport, anti-gravity pumping, and chemical microreaction on a tilted LIHSS. This work provides an efficient method to fabricate a promising platform for realizing directional water self-transport.

Subwavelength Quasi-Periodic Array for Infrared Antireflection.

Infrared antireflection of a zinc sulfide (ZnS) surface is important to improve performance of infrared detector systems. In this paper, double-pulse femtosecond laser micro-machining is proposed to fabricate a subwavelength quasi-periodic array (SQA) on ZnS substrate for infrared antireflection. The SQA consisting of approximately 30 million holes within a 2 × 2 cm2 area is uniformly formed in a short time. The double-pulse beam can effectively suppress the surface plasma shielding effect, resulting in obtaining a larger array depth. Further, the SQA depth is tunable by changing pulse energy and pulse delay, and can be used to readily regulate the infrared transmittance spectra as well as hydrophobicity. Additionally, the optical field intensity distributions of the SQA simulated by the rigorous coupled-wave analysis method indicate the modulation effect by the array depth. Finally, the infrared imaging quality captured through an infrared window embedded SQA is evaluated by a self-built infrared detection system.

Optical power auto-alignment method with eugenics sorting for enhancing the alignment speed and robustness of fiber-grating couplers.

To auto-couple optical devices, a simple but effective method must have a high success rate, fast scanning speed, and high stability. For coupling accuracy, swarm intelligence algorithms set a large number of particles to find the optimal point, which can introduce accelerated geometric errors in practical engineering. In this study, we proposed a method for auto-alignment between single-mode fibers and grating couplers using the particle swarm optimization algorithm, which introduces a chaotic mapping and eugenics mechanism. With the help of chaotic mapping and eugenics mechanisms, the scanning speed and robustness increased remarkably. A series of simulations and experiments showed that this method could increase the efficiency and robustness by 90% and 50%, respectively, compared to the basic swarm intelligence algorithm.

Fabrication and Sensing Application of Phase Shifted Bragg Grating Sensors.

As a special kind of Bragg grating, phase-shifted fiber Bragg grating (PS-FBG) has attracted extensive attention because of its extremely narrow transmission window and excellent sensing performance. The main purpose of this manuscript is to discuss the PS-FBG with special sensing characteristics and explore the influence of different inscription technologies on the sensing characteristics of PS-FBG by comparing the existing inscription methods. The sensing characteristics, advantages and disadvantages of PS-FBG with different structures are analyzed.

Flexible and Precise Droplet Manipulation by a Laser-Induced Shape Temperature Field on a Lubricant-Infused Surface.

Light actuation on a lubricant-infused surface (LIS) has attracted great attention because of its flexibility and remote control of droplet motion. However, to actuate a droplet on a LIS flexibly and precisely by light, the key issue is to control two degrees of freedom of the droplet motion in real time. In this paper, we propose a C-shape temperature field (CSTF) induced by rapid and selective laser irradiation on a LIS. The CSTF could not only manipulate a single droplet precisely and flexibly but also process multiple droplets automatically and orderly in real time. The mechanism showed that the droplet was confined by the Marangoni force in two orthogonal directions. For single droplet manipulation, the CSTF had the capability of correcting the off-track droplet motion. Moreover, the droplet motion, including rectilinear motion and curvilinear motion, could be precisely and flexibly controlled by the motion of the CSTF. For manipulation of multiple droplets, coalescence of multiple droplets was successfully achieved by triple rotating CSTFs. Such a method was applied in the detection of 5 µL of bovine serum albumin (BSA) by triggering chromogenic reactions automatically and orderly, which improved the efficiency of the whole process. We believe that this method is a significant candidate for intelligent droplet manipulation.

Advances in Laser Drilling of Structural Ceramics.

The high-quality, high-efficiency micro-hole drilling of structural ceramics to improve the thermal conductivity of hot-end parts or achieve high-density electronic packaging is still a technical challenge for conventional processing techniques. Recently, the laser drilling method (LDM) has become the preferred processing tool for structural ceramics, and it plays an irreplaceable role in the industrialized processing of group holes on structural ceramic surfaces. A variety of LDMs such as long pulsed laser drilling, short pulsed laser drilling, ultrafast pulsed laser drilling, liquid-assisted laser drilling, combined pulse laser drilling have been developed to achieved high-quality and high-efficiency micro-hole drilling through controlling the laser-matter interaction. This article reviews the characteristics of different LDMs and systematically compares the morphology, diameter, circularity, taper angle, cross-section, heat affect zone, recast layer, cracks, roughness, micro-nano structure, photothermal effect and photochemical reaction of the drilling. Additionally, exactly what processing parameters and ambient environments are optimal for precise and efficient laser drilling and their recent advancements were analyzed. Finally, a summary and outlook of the LDM technology are also highlighted.

High-quality welding of glass by a femtosecond laser assisted with silver nanofilm.

Glass products with high joint strength are highly demanded in the field of microelectromechanical system (MEMS). While the quality requirement of MEMS is getting higher and higher, much attention has been paid to further improving the welding strength of the glass. Herein, a femtosecond laser welding method assisted by silver nanofilm for quartz glass is proposed. To optimize the welding results, the influence of the laser power on the location of the heat-affected zone is studied. The effect of coated silver nanofilm at the interface of two glass substrates on femtosecond laser absorptivity is conducted. Also, the welding spot size under different irradiation periods is investigated. In addition, the welding strength with and without the silver nanofilm is measured and compared. It is demonstrated that the welding strength was increased nearly 20% on average by our proposed method compared with direct femtosecond laser welding. In addition, even at the lower laser power than the welding threshold, the welding process could be realized by the proposed method.

Robust Hierarchical Porous PTFE Film Fabricated via Femtosecond Laser for Self-Cleaning Passive Cooling.

Passive cooling materials that spontaneously cool an object are promising choices for mitigating the global energy crisis. However, these cooling effects are usually weakened or lost when dust contaminates the surface structure, greatly restricting their applications. In this work, a robust hierarchical porous polytetrafluoroethylene (PTFE) film with coral-like micro/nanostructures is generated by a facile and efficient femtosecond laser ablation technique. Owing to its unique micro/nanostructures, the as-prepared surface exhibits an outstanding self-cleaning function for various liquids with ultralow adhesion. This self-cleaning characteristic enhances the durability of its passive cooling effect. It is demonstrated that the titanium (Ti) sheet covered with laser-ablated PTFE film can realize a maximum temperature decrease of 4 and 10 °C compared to the Ti sheet covered with pristine PTFE film and uncovered, respectively. This study reveals that femtosecond laser micromachining is a facile and feasible avenue to produce robust self-cleaning passive cooling devices.

Sevoflurane inhibits the migration, invasion and induces apoptosis by regulating the expression of WNT1 via miR-637 in colorectal cancer.

Colorectal cancer (CRC) is a common malignancy. Sevoflurane has been reported to involve in the progression in several cancers. However, the molecular mechanism of sevoflurane in CRC progression remains unclear. Quantitative real-time PCR and western blot was used to detect the expression of miR-637 and WNT1. Cell migration, invasion and apoptosis were detected by transwell assay, flow cytometry or western blot, respectively. The interaction between WNT1 and miR-637 was confirmed by luciferase reporter assay, RNA immunoprecipitation assay and pull-down assay. We found sevoflurane could inhibit cell migration and invasion but induced apoptosis in CRC. Besides, the miR-637 level was decreased in CRC tissues and cells but could be rescued by sevoflurane. MiR-637 overexpression enhanced the anticancer functions of sevoflurane in CRC cells, while miR-637 inhibition showed opposite effects. WNT1 was confirmed to be a target of miR-637 and was inhibited by sevoflurane or miR-637. Importantly, knockdown of WNT1 reversed the carcinogenic effects mediated by miR-637 inhibitor in CRC cells treated with sevoflurane. Collectively, sevoflurane inhibited cell migration, invasion and induced apoptosis by regulating the miR-637/WNT1 axis in colorectal cancer, indicating a novel insight into the effective clinical implication for the anesthetic in CRC treatment.

Recent advances in femtosecond laser-structured Janus membranes with asymmetric surface wettability.

Janus wettability membranes have received much attention because of their asymmetric surface wettability. On the basis of this distinctiveness from traditional symmetrical membranes, relevant scholars have been inspired to pursue many innovations utilizing such membranes. Femtosecond laser microfabrication shows many advantages, such as precision, short time, and environmental friendliness, over traditional fabrication methods. Now this has been applied in structuring Janus membranes by researchers. This review covers recent advances in femtosecond laser-structured Janus membranes with asymmetric surface wettability. The background in femtosecond laser-structured Janus membranes is first discussed, focusing on the Janus wettability membrane and femtosecond laser microfabrication. Then the applications of Janus membranes are introduced, which are divided into unidirectional fluid transport, oil-water separation, fog harvesting, and seawater desalination. Finally, based on femtosecond laser-structured Janus membranes, some existing problems are pointed out and future perspectives proposed.