Effects of Heat Treatment on the Microstructure and Mechanical Properties of a Dual-Phase High-Entropy Alloy Fabricated via Laser Beam Power Bed Fusion.

To enhance the applicability of dual-phase high-entropy alloys (HEAs) like Fe32Cr33Ni29Al3Ti3, fabricated via laser beam power bed fusion (LB-PBF), a focus on improving their mechanical properties is essential. As part of this effort, heat treatment was explored. This study compares the microstructure and mechanical properties of the as-printed sample with those cooled in water after undergoing heat treatment at temperatures ranging from 1000 to 1200 °C for 1 h. Both pre- and post-treatment samples reveal a dual-phase microstructure comprising FCC and BCC phases. Although heat treatment led to a reduction in tensile and yield strength, it significantly increased ductility compared to the as-printed sample. This strength-ductility trade-off is related to changes in grain sizes with ultrafine grains enhancing strength and micron grains optimizing ductility, also influencing the content of FCC/BCC phases and dislocation density. In particular, the sample heat-treated at 1000 °C for 1 h and then water-cooled exhibited a better combination of strength and ductility, a yield strength of 790 MPa, and an elongation of 13%. This research offers innovative perspectives on crafting dual-phase HEA of Fe32Cr33Ni29Al3Ti3, allowing for tailorable microstructure and mechanical properties through a synergistic approach involving LB-PBF and heat treatment.

Generation of sub-100 fs pulses from a SESAM-NPE hybrid mode-locked Yb-doped fiber laser at a fundamental repetition rate of 1.15 GHz.

Supercontinuum generation via direct pumping of unamplified high-repetition-rate, sub-100 fs pulses with a pulse energy lower than 50 pJ is superior in noise performance and features a high acquisition speed. We demonstrate a novel, to the best of our knowledge, gigahertz-repetition-rate, mode-locked Yb-doped fiber laser, where the hybrid mode-locking approach is employed. The laser has a low initiating threshold of 300 mW and a broad mode-locking range of 600 mW (300-900 mW) in terms of pump power. The shortest obtained pulse width of the laser after compression is 95 fs, and the highest output pulse energy is 92.9 pJ at a fundamental repetition rate of 1.15 GHz. Moreover, the laser's output polarization states are switchable, and it has a polarization extinction ratio of 17.9 dB.

GHz-repetition-rate fundamentally mode-locked, isolator-free ring cavity Yb-doped fiber lasers with SESAM mode-locking.

A novel fundamentally mode-locked, GHz-repetition-rate ring cavity Yb-doped femtosecond fiber laser is demonstrated, which utilizes polarization-maintaining gain fiber and is enable by SESAM mode-locking. Thanks to the isolator-free structure, the ring cavity laser is operated bidirectionally and the two polarization-multiplexed output pulse trains are demonstrated synchronous. As a result, tunable waveforms one of which is with reduced pedestal and shorter pulse width in comparison with each individual, are generated by combination of the two orthogonal-polarized output pulses. Furthermore, a similar ring cavity structure that generates GHz picosecond pulses is demonstrated. We believe such high-repetition-rate polarization-multiplexed mode-locked fiber lasers could find further uses in various applications in need of gigahertz repetition rate and tunable waveforms.

A method to classify bone marrow cells with rejected option.

Bone marrow cell morphology has always been an important tool for the diagnosis of blood diseases. Still, it requires years of experience from a suitable person. Furthermore, the outcomes of their recognition are subjective and there is no objective quantitative standard. As a result, developing a deep learning automatic classification system for bone marrow cells is extremely important. However, typical classification machine learning systems only produce classification answers, and will not refuse to generate predictions when the prediction reliability is low. It will pose a big problem in some high-risk systems such as bone marrow cell recognition. This paper proposes a bone marrow cell classification method with rejected option (CMWRO) to classify 11 bone marrow cells. CMWRO is based on convolutional neural networks, ICP and SoftMax (CNN-ICP-SoftMax), containing a classifier with rejected option. When the rejected rate (RR) of tested samples is 0.3143, it can ensure that the precision, sensitivity, accuracy of the accepted samples reach 0.9921, 0.9917 and 0.9944 respectively. And the rejected samples will be handled by other ways, such as identified by doctors. Besides, the method has a good filtering effect on cell types that the classifier is not trained, such as abnormal cells and cells with less sample distribution. It can reach more than 82% in filtering efficiency. CMWRO improves the doctors' trust in the results of accepted samples to a certain extent. They only need to carefully identify the samples that CMWRO refuses to recognize, and finally combines the two results. It can greatly improve the efficiency and accuracy of bone marrow cell recognition.

Accuracy improvement in plastics classification by laser-induced breakdown spectroscopy based on a residual network.

The whole ecosystem is suffering from serious plastic pollution. Automatic and accurate classification is an essential process in plastic effective recycle. In this work, we proposed an accurate approach for plastics classification using a residual network based on laser-induced breakdown spectroscopy (LIBS). To increasing efficiency, the LIBS spectral data were compressed by peak searching algorithm based on continuous wavelet, then were transformed to characteristic images for training and validation of the residual network. Acrylonitrile butadiene styrene (ABS), polyamide (PA), polymethyl methacrylate (PMMA), and polyvinyl chloride (PVC) from 13 manufacturers were used. The accuracy of the proposed method in few-shot learning was evaluated. The results show that when the number of training image data was 1, the verification accuracy of classification by plastic type under residual network still kept 100%, which was much higher than conventional classification algorithms (BP, kNN and SVM). Furthermore, the training and testing data were separated from different manufacturers to evaluate the anti-interference properties of the proposed method from various additives in plastics, where 73.34% accuracy was obtained. To demonstrate the superiority of classification accuracy in the proposed method, all the evaluations were also implemented by using conventional classification algorithm (kNN, BP, SVM algorithm). The results confirmed that the residual network has a significantly higher accuracy in plastics classification and shows great potential in plastic recycle industries for pollution mitigation.

Analytical method for designing tunable terahertz absorbers with the desired frequency and bandwidth.

We present a novel and effective approach for designing and analyzing graphene metasurface-based terahertz absorbers with the desired central frequency and fractional bandwidth. Narrowband and broadband absorbers are designed using the same configuration with a single-layer of graphene ribbons deposited on a metal-backed dielectric film. An analytical circuit model derived for the graphene array applies the impedance matching concept to realize the desired terahertz absorber. Absorbers with a fractional bandwidth ranging from 10-100% are realized at the 1-THz central frequency. The results show excellent agreement with those calculated using full-wave numerical simulations. The proposed method is promising for terahertz imaging, sensing, and filtering applications.

Graphene metalens with dynamic focusing and plane focusing in the terahertz range.

We theoretically propose a high-efficiency tunable metalens based on an ellipse-shaped perforated graphene metasurface. By optimizing the axial length ratio of the elliptical aperture, we find the elliptical aperture with high reflectivity over a broad band by means of observing the reflectivity at different frequencies. Then, varying the orientation of the elliptical aperture from 0° to 180°, the reflected wave can generate a continuous 2π range phase shift while keeping its amplitude high, which is necessary to achieve focusing. The metalens exhibits extraordinary tunability of focal length via uniformly changing the Fermi energy of graphene. The focus can be shifted above 72 µm with focusing efficiency reaching over 70%. In addition, the tunable metalens is also capable of broadband focusing modulation and plane focusing. The presented metalens exhibits outstanding focusing efficiency in dynamic focusing, thereby manifesting great practicability in dynamic imaging and robust stable imaging.

Processing Technologies and Properties of Cu-10Sn Formed by Selective Laser Melting Combined with Heat Treatment.

The selective laser melting (SLM) process of the Cu-10Sn alloy and effects of heat treatment were examined in this study. The Taguchi test and Box-Behnken design were performed to determine the laser power (LP), scanning speed (SS), and hatch space (HS). The best process parameters were selected using the highest density: the optimum HS was 160 µm; SS was 278 mm s-1; LP was 192 W; and density reached 98.76%. The tensile strength, elongation, Vickers hardness, and impact toughness of the Cu-10Sn alloy formed by SLM are 435 MPa, 13%, 122HV1, and 10 J·cm-2, respectively. Heat treatment can significantly increase the ductility and impact toughness of the Cu-10Sn alloy, but at the same time, it can reduce its strength. The strength of parts obtained by all five heat treatment methods is much greater than that of castings. Parts that are annealed at 600°C for 4 h have the best mechanical properties, its tensile strength and elongation were 378 MPa and 15%, respectively.

Design of Dual-Band Terahertz Perfect Metamaterial Absorber Based on Circuit Theory.

We present a novel strategy for designing a dual-band absorber based on graphene metasurface for terahertz frequencies. The absorber consists of a two-dimensional array of patches deposited on a metal-backed dielectric layer. Using an analytical circuit model, we obtain closed-form relatinos for the geometrical parameters of the absorber and the properties of the applied materials to achieve the dual-band absorber. Two absorption bands with perfect absorption at the preset frequencies of 0.5 and 1.5 THz are achieved. The results obtained by the analytical circuit model are compared to the simulations carried out by full-wave electromagnetic field analysis. The agreement between results is very good. We demonstrate that the graphene absorber remains as the dual band for a wide range of the chemical potential. Furthermore, the recommended dual band absorber is insensitive in terms of polarization and remain within various incident angles.

All-polarization-maintaining, all-normal-dispersion mode-locked fiber laser with spectral filtering in a nonlinear optical loop mirror.

The spectral filtering effect is essential to dissipative dynamics in an all-normal-dispersion (ANDi) mode-locked fiber laser. In this study, we numerically and experimentally demonstrate the spectral filtering process of a nonlinear optical loop mirror (NOLM). Taking advantage of the 40/60 NOLM's spectral filtering ability, we designed a novel all-polarization-maintaining ANDi mode-locked fiber laser without using a separate spectral filter. The NOLM functions as an artificial saturable absorber and a spectral filter in an ANDi cavity. During mode locking, we observed that the NOLM decreased the spectral width of the pulse from 5.46 to 4.38 nm. The fiber laser generated 509-fs compressed pulses at the repetition rate of 13.4 MHz. Our work provides a promising novel and compact ANDi fiber laser for ultrafast photonic applications.

Investigation of the reaction mechanism and optical transparency in nanosecond laser welding of glasses assisted with titanium film.

The welding of glasses is widely used in many fields, such as optics, microfluidics, and microelectromechanical systems. In this paper, two pieces of 1 mm soda lime glass substrates were welded using a 1064 nm nanosecond laser assisted with a 14 nm titanium-coated thin film coating. Results show that after the laser irradiation, the welded area becomes highly transparent much like uncoated glass. The maximum change rate of transmittance of the welded zone is 8.88% in the wavelength range of 400-1800 nm, compared to a piece of 2 mm glass substrate. The chemical reaction process between the titanium film and the glass substrate of the highly transparent welded sample was analyzed by x-ray photoelectron spectroscopy. Welded quality and shear strength were characterized by scanning acoustic microscopy and shear tests.

A Simple and Efficient Method for Designing Broadband Terahertz Absorber Based on Singular Graphene Metasurface.

In this paper, we propose a simple and efficient method for designing a broadband terahertz (THz) absorber based on singular graphene patches metasurface and metal-backed dielectric layer. An accurate circuit model of graphene patches is used for obtaining analytical expressions for the input impedance of the proposed absorber. The input impedance is designed to be closely matched to the free space in a wide frequency range. Numerical simulation and analytical circuit model results consistently show that graphene metasurface-based THz absorber with an absorption value above 90% in a relative bandwidth of 100% has been achieved.

Experimental investigation of laser-induced breakdown spectroscopy assisted with laser-induced fluorescence for trace aluminum detection in steatite ceramics.

Laser-induced breakdown spectroscopy (LIBS) assisted with laser-induced fluorescence (LIF) was introduced to detect trace aluminum in steatite ceramics in this work. The mechanism and transition process of laser-induced aluminum atomic fluorescence in laser-induced plasma was described and discussed. Selective enhancement of LIF and temporal synchronicity between radiation laser and fluorescence were studied. The influences of ablation laser energy, power density of the radiation laser, and interpulse delay were experimentally investigated. The results showed that 60 mJ in ablation laser energy and 4 µs in interpulse delay were the optimal choice for fluorescent intensity. The fluorescence was increased to the saturation level over 4 MW/cm2. Spectral stability improvement of LIBS-LIF was also discovered in this work. The results proved that LIBS-LIF is a feasible and effective modification of LIBS for ceramics analysis.

Sensitive determination of silicon contents in low-alloy steels using micro laser-induced breakdown spectroscopy assisted with laser-induced fluorescence.

Silicon element plays an important role in strength and hardness improvement in steels, but is harmful for ductility, tenacity, and anti-corrosion. Therefore, silicon content should be fast determined in steel manufacture to keep silicon in moderation. In this work, micro laser-induced breakdown spectroscopy assisted with laser-induced fluorescence (µLIBS-LIF) was proposed to sensitively determine silicon in low-alloy steels. The mechanism and excitation selection of laser-induced silicon atomic fluorescence in laser-induced plasma were discussed. Under 10 µm laser-ablated scatters, the results showed that µLIBS-LIF had analytical performance with R2 of 0.9998, LoD of 2.8 µg g-1, and RMSECV of 63 µg g-1, significantly better than µLIBS under their respective optimal conditions. The analytical sensitivity in µLIBS-LIF was even better than macro LIBS in others' works. As our best knowledge, the silicon LoD in LIBS technique was improved to better than 10 µg g-1 in steel matrix for the first time. This work demonstrates µLIBS-LIF as a capable and potential approach for fast determining silicon element in steel industries.

870 fs, 448 kHz pulses from an all-polarization-maintaining Yb-doped fiber laser with a nonlinear amplifying loop mirror.

We demonstrate a mode-locked long all-polarization-maintaining fiber laser with a nonlinear amplifying loop mirror. The fiber oscillator directly delivers 221 ps chirped pulses at the repetition rate of 448 kHz. The pulses can be further amplified up to 134 nJ and compressed down to 870 fs by a grating pair. This kind of laser is self-starting and stable long term, and it has potential application in high-power fiber amplification for industrial applications.