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<jats:p>We have numerically and experimentally observed the soliton pulsation with obvious breathing behavior in the anomalous fiber laser mode-locked by a nonlinear polarization rotation technique. The numerical study of the soliton pulsation with breathing behavior was analyzed through the split-step Fourier method at first, and it was found that the phase difference caused by the polarization controller would affect the breathing characteristics. Then, taking advantage of the dispersive Fourier transform technique, we confirmed the breathing characteristic of soliton pulsation in the same fiber laser as the simulation model experimentally. These results complement the research on the breathing characteristic of soliton pulsation.</jats:p>

<jats:p>We propose a novel scheme for THz wave generation by repeated and continuous frequency conversions from pump wave to high-order Stokes waves (HSWs). The repeated frequency conversions are accomplished by oscillations of Stoke waves in resonant cavity (RC) where low-order Stokes waves (LSWs) are converted to high-order Stokes waves again and again. The continuous frequency conversions are accomplished by optimized cascaded difference frequency generation (OCDFG) where the poling periods of the optical crystal are aperiodic leading to the frequency conversions from low-order Stokes waves to high-order Stokes waves uninterruptedly and unidirectionally. Combined with the repeated and continuous frequency conversions, the optical-to-THz energy conversion efficiency (OTECE) exceeds 26% at 300 K and 43% at 100 K with pump intensities of 300 MW/cm<jats:sup>2</jats:sup>.</jats:p>

<jats:p>Ultrasonic guided waves (UGWs), which propagate throughout the entire thickness of cortical bone, are attractive for the early diagnosis of osteoporosis. However, this is challenging due to the impact of soft tissue and the inherent difficulties related to multiparametric inversion of cortical bone quality factors, such as cortical thickness and bulk wave velocity. Therefore, in this research, a UGW-based multi-parameter inversion algorithm is developed to predict strength-related factors. In simulation, a free plate (cortical bone) and a bilayer plate (soft tissue and cortical bone) are used to validate the proposed method. The inversed cortical thickness (CTh), longitudinal velocity (<jats:italic>V</jats:italic> <jats:sub>L</jats:sub>) and transverse velocity (<jats:italic>V</jats:italic> <jats:sub>T</jats:sub>) are in accordance with the true values. Then four bovine cortical bone plates were used in <jats:italic>in vitro</jats:italic> experiments. Compared with the reference values, the relative errors for cortical thickness were 3.96%, 0.83%, 2.87%, and 4.25%, respectively. In the <jats:italic>in vivo</jats:italic> measurements, UGWs are collected from the tibias of 10 volunteers. The theoretical dispersion curves depicted by the estimated parameters (<jats:italic>V</jats:italic> <jats:sub>T</jats:sub>, <jats:italic>V</jats:italic> <jats:sub>L</jats:sub>, CTh) match well with the extracted experimental ones. In comparison with dual-energy x-ray absorptiometry, our results show that the estimated transverse velocity and cortical thickness are highly sensitive to osteoporosis. Therefore, these two parameters (CTh and <jats:italic>V</jats:italic> <jats:sub>T</jats:sub>) of long bones have potential to be used for diagnosis of bone status in clinical applications.</jats:p>

<jats:p>Through diagnosing the plasma density and calculating the intensity of microwave electric field, four 10 cm electron cyclotron resonance (ECR) ion sources with different magnetic field structures are studied to reveal the inside interaction between the plasma, magnetic field and microwave electric field. From the diagnosing result it can be found that the plasma density distribution is controlled by the plasma generation and electron loss volumes associated with the magnetic field and microwave power level. Based on the cold plasma hypothesis and diagnosing result, the microwave electric field intensity distribution in the plasma is calculated. The result shows that the plasma will significantly change the distribution of the microwave electric field intensity to form a bow shape. From the boundary region of the shape to the center, the electric field intensity varies from higher to lower and the diagnosed density inversely changes. If the bow and its inside lower electric field intensity region are close to the screen grid, the performance of ion beam extracting will be better. The study can provide useful information for the creating of 10 cm ECR ion source and understanding its mechanism.</jats:p>

<jats:p>We study the characteristics of plasma–wave interaction in helicon plasmas near the lower hybrid frequency. The (0D) dispersion relation is derived to analyze the properties of the wave propagation and a 1D cylindrical plasma–wave interaction model is established to investigate the power deposition and to implement the parametric analysis. It is concluded that the lower hybrid resonance is the main mechanism of the power deposition in helicon plasmas when the RF frequency is near the lower hybrid frequency and the power deposition mainly concentrates on a very thin layer near the boundary. Therefore, it causes that the plasma resistance has a large local peak near the lower hybrid frequency and the variation of the plasma density and the parallel wavenumber lead to the frequency shifting of the local peaks. It is found that the magnetic field is still proportional to the plasma density for the local maximum plasma resistance and the slope changes due to the transition.</jats:p>

<jats:p>Germanium diselenide (GeSe<jats:sub>2</jats:sub>) is a promising candidate for electronic devices because of its unique crystal structure and optoelectronic properties. However, the evolution of lattice and electronic structure of <jats:italic>β</jats:italic>-GeSe<jats:sub>2</jats:sub> at high pressure is still uncertain. Here we prepared high-quality <jats:italic>β</jats:italic>-GeSe<jats:sub>2</jats:sub> single crystals by chemical vapor transfer (CVT) technique and performed systematic experimental studies on the evolution of lattice structure and bandgap of <jats:italic>β</jats:italic>-GeSe<jats:sub>2</jats:sub> under pressure. High-precision high-pressure ultra low frequency (ULF) Raman scattering and synchrotron angle-dispersive x-ray diffraction (ADXRD) measurements support that no structural phase transition exists under high pressure up to 13.80 GPa, but the structure of <jats:italic>β</jats:italic>-GeSe<jats:sub>2</jats:sub> turns into a disordered state near 6.91 GPa and gradually becomes amorphous forming an irreversibly amorphous crystal at 13.80 GPa. Two Raman modes keep softening abnormally upon pressure. The bandgap of <jats:italic>β</jats:italic>-GeSe<jats:sub>2</jats:sub> reduced linearly from 2.59 eV to 1.65 eV under pressure with a detectable narrowing of 36.5%, and the sample under pressure performs the piezochromism phenomenon. The bandgap after decompression is smaller than that in the atmospheric pressure environment, which is caused by incomplete recrystallization. These results enrich the insight into the structural and optical properties of <jats:italic>β</jats:italic>-GeSe<jats:sub>2</jats:sub> and demonstrate the potential of pressure in modulating the material properties of two-dimensional (2D) Ge-based binary material.</jats:p>

<jats:p>Integration of the high-quality GaSb layer on an Si substrate is significant to improve the GaSb application in optoelectronic integration. In this work, a suitable ion implantation fluence of 5 × 10<jats:sup>16</jats:sup>-cm<jats:sup>−2</jats:sup> H ions for GaSb layer transfer is confirmed. Combining the strain change and the defect evolution, the blistering and exfoliation processes of GaSb during annealing is revealed in detail. With the direct wafer bonding, the GaSb layer is successfully transferred onto a (100) Si substrate covered by 500-nm thickness thermal oxide SiO<jats:sub>2</jats:sub> layer. After being annealed at 200 °C, the GaSb layer shows high crystalline quality with only 77 arcsec for the full width at half maximum (FWHM) of the x-ray rocking curve (XRC).</jats:p>

<jats:p>Introducing voids into AlN layer at a certain height using a simple method is meaningful but challenging. In this work, the AlN/sapphire template with AlN interlayer structure was designed and grown by metal-organic chemical vapor deposition. Then, the AlN template was annealed at 1700 °C for an hour to introduce the voids. It was found that voids were formed in the AlN layer after high-temperature annealing and they were mainly distributed around the AlN interlayer. Meanwhile, the dislocation density of the AlN template decreased from 5.26 × 10<jats:sup>9</jats:sup> cm<jats:sup>−2</jats:sup> to 5.10 × 10<jats:sup>8</jats:sup> cm<jats:sup>−2</jats:sup>. This work provides a possible method to introduce voids into AlN layer at a designated height, which will benefit the design of AlN-based devices.</jats:p>

<jats:p>Direct visualization of the structural defects in two-dimensional (2D) semiconductors at a large scale plays a significant role in understanding their electrical/optical/magnetic properties, but is challenging. Although traditional atomic resolution imaging techniques, such as transmission electron microscopy and scanning tunneling microscopy, can directly image the structural defects, they provide only local-scale information and require complex setups. Here, we develop a simple, non-invasive wet etching method to directly visualize the structural defects in 2D semiconductors at a large scale, including both point defects and grain boundaries. Utilizing this method, we extract successfully the defects density in several different types of monolayer molybdenum disulfide samples, providing key insights into the device functions. Furthermore, the etching method we developed is anisotropic and tunable, opening up opportunities to obtain exotic edge states on demand.</jats:p>

<jats:p>Since the discovery of transition metal dichalcogenide (TMDC) nanoparticles (NPs) with the onion-like structure, many efforts have been made to develop their fabrication methods. Laser fabrication (LF) is one of the most promising methods to prepare onion-structured TMDC (or OS-TMDC) NPs due to its green, flexible, and scalable syntheses. In this mini-review article, we systematically introduce various laser-induced OS-TMDC (especially the OS-MoS<jats:sub>2</jats:sub>) NPs, their formation mechanism, properties, and applications. The preparation routes mainly include laser ablation in liquids and atmospheres, and laser irradiation in liquids. The various formation mechanisms are then introduced based on the different preparation routes, to describe the formations of the corresponding OS-NPs. Finally, some interesting properties and novel applications of these NPs are briefly demonstrated, and a short outlook is also given. This review could help to understand the progress of the laser-induced OS-TMDC NPs and their applications.</jats:p>