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<jats:p>We present a high-dispersive multilayer mirror for pulse stretching in a femtosecond fiber laser amplification system. The designed mirror contains 54 layers with a total physical thickness of 7.3 μm, which can provide a positive group delay dispersion (GDD) of 600 fs<jats:sup>2</jats:sup> and a high reflectance over 99.9% from 1010 to 1070 nm. The samples were prepared by dual ion beam sputtering. The measured transmittance matches well with the theoretical result. The GDD characteristics of samples were tested by home-made white light interferometer. The measured GDD is higher than the design results, an average GDD of +722 fs<jats:sup>2</jats:sup> from 1010 nm to 1070 nm. The mirrors were employed in a Yb-doped large-mode-area photonic crystal fiber amplification system. An input pulse compressed by the gratings with autocorrelation function of 83 fs is obtained with a stretched FWHM of 1.29 ps after 28 bounces between the dispersive mirrors. The results show that the multilayer dispersive mirror could be an effective and promising technique for pulse stretching in femtosecond amplification systems.</jats:p>

<jats:p>Different MoS<jats:sub>2</jats:sub>/Au heterostructures can play an important role in tuning the photoluminescence (PL) and optoelectrical properties of monolayer MoS<jats:sub>2</jats:sub>. Previous studies of PL of MoS<jats:sub>2</jats:sub>/Au heterostructures were mainly limited to the PL enhancement by using different Au nanostructures and PL quenching of monolayer MoS<jats:sub>2</jats:sub> on flat Au surfaces. Here, we demonstrate the enhanced excitonic PL emissions of monolayer MoS<jats:sub>2</jats:sub>/Au heterostructures on Si/SiO<jats:sub>2</jats:sub> substrates. By transferring the continuous monolayer MoS<jats:sub>2</jats:sub> onto a stepped Au structure consisting of 60-nm and 100-nm Au films, the MoS<jats:sub>2</jats:sub>/Au-60 and MoS<jats:sub>2</jats:sub>/Au-100 heterostructures exhibit enhanced PL emissions, each with a blue-shifted PL peak in comparison with the MoS<jats:sub>2</jats:sub>/SiO<jats:sub>2</jats:sub>. Furthermore, the PL intensity of MoS<jats:sub>2</jats:sub>/Au-60 is about twice larger than that of MoS<jats:sub>2</jats:sub>/Au-100. The different enhanced excitonic PL emissions in MoS<jats:sub>2</jats:sub>/Au heterostructures can be attributed to the different charge transfer effects modified by the stepped Au structure. This work may provide an insight into the excitonic PL and charge transfer effect of MoS<jats:sub>2</jats:sub> on Au film and yield novel phenomena in MoS<jats:sub>2</jats:sub>/Au heterostructures for further study of PL tuning and optoelectrical properties.</jats:p>

<jats:p>The dual-channel nearly perfect absorption is realized by the coupled modes of topological interface states (TIS) in the near-infrared range. An all-dielectric layered heterostructure composed of photonic crystals (PhC)/graphene/PhC/graphene/PhC on GaAs substrate is proposed to excite the TIS at the interface of adjacent PhC with opposite topological properties. Based on finite element method (FEM) and transfer matrix method (TMM), the dual-channel absorption can be modulated by the periodic number of middle PhC, Fermi level of graphene, and angle of incident light (TE and TM polarizations). Especially, by fine-tuning the Fermi level of graphene around 0.4 eV, the absorption of both channels can be switched rapidly and synchronously. This design is hopefully integrated into silicon-based chips to control light.</jats:p>

<jats:p>We study the effect of linearly polarized light on the band structure and longitudinal conductivity in ABC-stacked trilayer graphene. The linearly polarized light can induce a pair of additional points in ABC-stacked trilayer graphene, where conduct and valence bands touch. The locations of these points are determined by the amplitude of the light. Furthermore, the layer pseudospin polarization can be controlled by the light. When the Fermi energy locates at Dirac points, i.e., <jats:italic>E</jats:italic> <jats:sub>f</jats:sub> = 0, the longitudinal conductivity shows resonance phenomena when the light is present. Away from the Dirac points, the longitudinal conductivity is unchanged as varying <jats:italic>E</jats:italic> <jats:sub>f</jats:sub> for weak light field at larger Fermi energy, and the amplitude of longitudinal conductivity can be controlled by tuning the light field amplitude. Moreover, the effect of linearly polarized light on resonance phenomena in <jats:italic>k</jats:italic>-cubic Rashba–Dresselhaus system under the irradiating of linearly polarized light is discussed.</jats:p>

<jats:p>Compared to conventional devices, metasurfaces offer the advantages of being lightweight, with planarization and tuning flexibility. This provides a new way to integrate and miniaturize optical systems. In this paper, a metasurface capable of generating multiple bottle beams was designed. Based on the Pancharatnam–Berry (P–B) phase principle, the metasurface lens can accurately control the wavefront by adjusting the aspect ratio of the titanium dioxide nanopillars and the rotation angle. When irradiated by left-handed circularly polarized light with a wavelength of 632.8 nm, the optical system can produce multiple micron bottle beams. Taking two bottle beams as examples, the longitudinal full widths at half-maximum of the optical tweezers can reach 0.85 μm and 1.12 μm, respectively, and the transverse full widths at half-maximum can reach 0.46 μm and 0.6 μm. Also, the number of generated bottle beams can be varied by controlling the size of the annular obstacle. By changing the <jats:italic>x</jats:italic>-component of the unit rotation angle, the metasurface can also change the shape of the bottle beam — the beam cross-section can be changed from circular to elliptical. This paper also analyzes the trapping of ytterbium atoms by the multi bottle beam acting as optical tweezers. It is found that the multi bottle beam can cool and trap multiple ytterbium atoms.</jats:p>

<jats:p>An n-GaO<jats:sub> <jats:italic>x</jats:italic> </jats:sub> thin film is deposited on a single-crystal boron-doped diamond by RF magnetron sputtering to form the pn heterojunction. The n-GaO<jats:sub> <jats:italic>x</jats:italic> </jats:sub> thin film presents a small surface roughness and a large optical band gap of 4.85 eV. In addition, the band alignment is measured using x-ray photoelectron spectroscopy to evaluate the heterojunction properties. The GaO<jats:sub> <jats:italic>x</jats:italic> </jats:sub>/diamond heterojunction shows a type-II staggered band configuration, where the valence and conduction band offsets are 1.28 eV and 1.93 eV, respectively. These results confirm the feasibility of the use of n-GaO<jats:sub> <jats:italic>x</jats:italic> </jats:sub> as a termination structure for diamond power devices.</jats:p>

<jats:p>Photons with variable energy, high coherency, and switchable polarization provide an ideal tool-kits for exploring the cutting-edge scientific questions in the condensed matter physics and material sciences. Over decades, extensive researches in the sample fabrication and excitation have employed the photon as one of the important means to synthesize and explore the low-dimensional quantum materials. In this review, we firstly summarize the recent progresses of the state-of-the-art thin-film deposition methods using excimer pulsed laser, by which syntactic oxides with atomic-unit-cell-thick layers and extremely high crystalline quality can be programmatically fabricated. We demonstrate that the artificially engineered oxide quantum heterostructures exhibit the unexpected physical properties which are absent in their parent forms. Secondly, we highlight the recent work on probing the symmetry breaking at the surface/interface/interior and weak couplings among nanoscale ferroelectric domains using optical second harmonic generation. We clarify the current challenges in the <jats:italic>in-situ</jats:italic> characterizations under the external fields and large-scale imaging using optical second harmonic generation. The improvements in the sample quality and the non-contact detection technique further promote the understanding of the mechanism of the novel properties emerged at the interface and inspire the potential applications, such as the ferroelectric resistive memory and ultrahigh energy storage capacitors.</jats:p>

<jats:p>Non-contact atomic force microscope is a powerful tool to investigate the surface topography with atomic resolution. Here we propose a new approach to estimate the interaction between its tips and samples, which combines a semi-empirical model with density functional theory (DFT) calculations. The generated frequency shift images are consistent with the experiment for mapping organic molecules using CuCO, Cu, CuCl, and CuO<jats:sub> <jats:italic>x</jats:italic> </jats:sub> tips. This approach achieves accuracy close to DFT calculation with much lower computational cost.</jats:p>

<jats:p>The recent experimental observation of topological magnon insulator states in a superconducting circuit chain marks a breakthrough for topological physics with qubits, in which a dimerized qubit chain has been realized. Here, we extend such a dimer lattice to superlattice with arbitrary number of qubits in each unit cell in superconducting circuits, which exhibits rich topological properties. Specifically, by considering a quadrimeric superlattice, we show that the topological invariant (winding number) can be effectively characterized by the dynamics of the single-excitation quantum state through time-dependent quantities. Moreover, we explore the appearance and detection of the topological protected edge states in such a multiband qubit system. Finally, we also demonstrate the stable Bloch-like-oscillation of multiple interface states induced by the interference of them. Our proposal can be readily realized in experiment and may pave the way towards the investigation of topological quantum phases and topologically protected quantum information processing.</jats:p>

<jats:p>We examined the wake-up effect in a TiN/Hf<jats:sub>0.4</jats:sub>Zr<jats:sub>0.6</jats:sub>O<jats:sub>2</jats:sub>/TiN structure. The increased polarization was affected by the cumulative duration of a switched electric field and the single application time of the field during each switching cycle. The space-charge-limited current was stable, indicating that the trap density did not change during the wake-up. The effective charge density in the space-charge region was extracted from capacitance–voltage curves, which demonstrated an increase in free charges at the interface. Based on changing characteristics in these properties, the wake-up effect can be attributed to the redistribution of oxygen vacancies under the electric field.</jats:p>