We report a high-average-power acousto-optic (AO) Q-switched intracavity frequency-doubled red laser based on a high-efficiency light-emitting-diode (LED) pumped two-rod Nd,Ce:YAG laser module. Under quasi-continuous wave operation conditions, a maximum output power of 1319.08 nm wavelength was achieved at 11.26 W at a repetition rate of 100 Hz, corresponding to a maximum optical efficiency of 13.9% and a slope efficiency of 17.9%. In the active Q-switched regime, the pulse energy of the laser was as high as 800 µJ at a repetition rate of 10 kHz with a pulse width of 1.5 µs. Under non-critical phase-matched KTP crystal conditions, an average power of 2.03 W of 658.66 nm through intracavity frequency-doubling was obtained at a repetition frequency of 10 kHz with a duration of 1.3 µs, and the $M^{2}$ factor was measured to be about 5.8. To the best of our knowledge, this is the highest average power of an LED-pumped AO Q-switched 1319 nm laser and intracavity frequency-doubled red laser reported to date.

Fiber-reinforced composites possess anisotropic mechanical and heat transfer properties due to their anisotropic fibers and structure distribution. In C/SiC composites, the out-of-plane thermal conductivity has mainly been studied, whereas the in-plane thermal conductivity has received less attention due to their limited thickness. In this study, the slab module of a transient plane source method is adopted to measure the in-plane thermal conductivity of a 2D plain woven C/SiC composite slab, and the test uncertainty is analyzed numerically. The numerical investigation proves that the slab module is reliable for measuring the isotropic and anisotropic slabs with in-plane thermal conductivity greater than 10 W$\cdot$m$^{-1}\cdot $K$^{-1}$. The anisotropic thermal conductivity of the 2D plain woven C/SiC composite slab is obtained within the temperature range of 20–900 ℃ by combining with a laser flash analysis method to measure the out-of-plane thermal conductivity. The results demonstrate that the out-of-plane thermal conductivity of C/SiC composite decreases with temperature, while its in-plane thermal conductivity first increases with temperature and then decreases, and the ratio of in-plane thermal conductivity to out-of-plane thermal conductivity is within 2.2–3.1.

Relativistic femtosecond mid-infrared pulses can be generated efficiently by laser interaction with near-critical-density plasmas. It is found theoretically and numerically that the radiation pressure of a circularly polarized laser pulse first compresses the plasma electrons to form a dense flying mirror with a relativistic high speed. The pulse reflected by the mirror is red-shifted to the mid-infrared range. Full three-dimensional simulations demonstrate that the central wavelength of the mid-infrared pulse is tunable from 3 µm to 14 µm, and the laser energy conversion efficiency can reach as high as 13$\%$. With a 0.5–10 PW incident laser pulse, the generated mid-infrared pulse reaches a peak power of 10–180 TW, which is interesting for various applications in ultrafast and high-field sciences.

In the existing ghost-imaging-based cryptographic key distribution (GCKD) protocols, the cryptographic keys need to be encoded by using many modulated patterns, which undoubtedly incurs long measurement time and huge memory consumption. Given this, based on snapshot compressive ghost imaging, a public network cryptographic key distribution protocol is proposed, where the cryptographic keys and joint authentication information are encrypted into several color block diagrams to guarantee security. It transforms the previous single-pixel sequential multiple measurements into multi-pixel single exposure measurements, significantly reducing sampling time and memory storage. Both simulation and experimental results demonstrate the feasibility of this protocol and its ability to detect illegal attacks. Therefore, it takes GCKD a big step closer to practical applications.

Based on the numerical solution of the time-dependent Dirac equation, we propose a method to observe in real time the ac Stark shift of a vacuum driven by an ultra-intense laser field. By overlapping the ultra-intense pump pulse with another zeptosecond probe pulse whose photon energy is smaller than $2mc^2$, electron–positron pair creation can be controlled by tuning the time delay between the pump and probe pulses. Since the pair creation rate depends sensitively on the instantaneous vacuum potential, one can reconstruct the ac Stark shift of the vacuum potential according to the time-delay-dependent pair creation rate.

A D-shaped fiber is coated with a new two-dimensional nanomaterial, violet phosphorus (VP), to create a saturable absorber (SA) with a modulation depth of 3.68%. Subsequently, the SA is inserted into a fiber laser, enabling successful generation of dark solitons and bright–dark soliton pairs through adjustment of the polarization state within the cavity. Through further study, mode-locked pulses are achieved, proving the existence of polarization-locked vector solitons. The results indicate that VP can be used as a polarization-independent SA.

A quasi-phase-matched technique is introduced for soliton transmission in a quadratic $[\chi^{(2)}]$ nonlinear crystal to realize the stable transmission of dipole solitons in a one-dimensional space under three-wave mixing. We report four types of solitons as dipole solitons with distances between their bimodal peaks that can be laid out in different stripes. We study three cases of these solitons: spaced three stripes apart, one stripe apart, and confined to the same stripe. For the case of three stripes apart, all four types have stable results, but for the case of one stripe apart, stable solutions can only be found at $\omega_{1}=\omega_{2}$, and for the condition of dipole solitons confined to one stripe, stable solutions exist only for Type1 and Type3 at $\omega_{1}=\omega_{2}$. The stability of the soliton solution is solved and verified using the imaginary time propagation method and real-time transfer propagation, and soliton solutions are shown to exist in the multistability case. In addition, the relations of the transportation characteristics of the dipole soliton and the modulation parameters are numerically investigated. Finally, possible approaches for the experimental realization of the solitons are outlined.

By numerically solving the two-dimensional semiconductor Bloch equation, we study the high-order harmonic emission of a monolayer ZnO under the driving of co-rotating two-color circularly polarized laser pulses. By changing the relative phase between the fundamental frequency field and the second one, it is found that the harmonic intensity in the platform region can be significantly modulated. In the higher order, the harmonic intensity can be increased by about one order of magnitude. Through time-frequency analysis, it is demonstrated that the emission trajectory of monolayer ZnO can be controlled by the relative phase, and the harmonic enhancement is caused by the second quantum trajectory with the higher emission probability. In addition, near-circularly polarized harmonics can be generated in the co-rotating two-color circularly polarized fields. With the change of the relative phase, the harmonics in the platform region can be altered from left-handed near-circularly polarization to right-handed one. Our results can obtain high-intensity harmonic radiation with an adjustable ellipticity, which provides an opportunity for syntheses of circularly polarized attosecond pulses.

We experimentally and theoretically present a paradigm for the accurate bilayer design of gradient metasurfaces for wave beam manipulation, producing an extremely asymmetric splitting effect by simply tailoring the interlayer size. This concept arises from anomalous diffraction in phase gradient metasurfaces and the precise combination of the phase gradient in bilayer metasurfaces. Ensured by different diffraction routes in momentum space for incident beams from opposite directions, extremely asymmetric acoustic beam splitting can be generated in a robust way, as demonstrated in experiments through a designed bilayer system. Our work provides a novel approach and feasible platform for designing tunable devices to control wave propagation.

We investigate the harmonic emission from bichromatic periodic potential by numerically solving the time-dependent Schrödinger equation in the velocity gauge. The results show that the harmonic minimum is sensitive to the wavelength. Moreover, distinct crystal momentum states contribute differently to harmonic generation. In momentum space, the electron dynamics reveal a close relationship between the spectral minimum and the electron distribution in higher conduction bands. Additionally, by introducing an ultraviolet pulse to the fundamental laser field, the suppression of the harmonic minimum occurs as a result of heightened electron populations in higher conduction bands. This work sheds light on the harmonic emission originating from a solid with a two-atom basis.

Tungsten sulphoselenide (WSSe) alloys, belonging to the transition metal dichalcogenide family, have attracted significant interest in the area of optoelectronics because of their unique optical and electronic properties. However, there has been a dearth of sufficient research on the saturable absorption features and ultrafast lasers applications. Herein, we fabricated a WSSe-microfiber saturable absorber (SA) based on WSSe nanosheets prepared by liquid exfoliation technique. The SA provided a saturation intensity of a modulation depth of 27.95% and a nonsaturable loss of 21.34%. To investigate the potential applications of WSSe in ultrafast photonics, the prepared WSSe-microfiber was incorporated into an Er-doped fiber laser ring cavity. The results demonstrated that the WSSe-based SA successfully generated mode-locking laser pulses with a remarkably short pulse width of 231 fs. Furthermore, the output power of this ultrafast fiber laser reached an impressive value of 15.68 mW. These findings provide valuable views into the unique features of WSSe alloys in the areas of ultrafast optics and develop recipes for SA in ultrafast fiber lasers.

Interactions among optical solitons can be used to develop photonic information processing devices such as all-optical switches and all-optical logic gates. It is the key to achieve high-speed, high-capacity all-optical networks and optical computers, which is also important in academy. We study the properties of all-optical switches of optical solitons in birefringent fibers, based on the coupled nonlinear Schrödinger equations. It is found that under different initial conditions we can achieve all-optical switching functions. We also study the influence of different physical parameters of birefringent fibers on all-optical soliton switching. The relevant conclusions are conducive to achieving the all-optical switching function of optical solitons in birefringent fibers, providing useful guidance for widespread applications of optical soliton all-optical switches in birefringent fibers of communications.

We demonstrate a method to realize unidirectional negative refraction in an acoustic parity-time ($PT$)-symmetric system, which is composed of a pair of metasurfaces sandwiching an air gap. The pair of metasurfaces possesses loss and gain modulations. The unidirectional negative refraction, which is strictly limited to the case of incident wave imposing on the loss end of the metasurface, is demonstrated at the exception point (EP) in this $PT$-symmetric system, while the incidence from the other side leads to strong reflection. Based on rigorous calculations, we explicitly show the underlying mechanism of this model to achieve unidirectional wave scatterings around the EP in the parametric space. In addition, the perfect imaging of a point source in the three-dimensional space, as a signature of negative refraction, is simulated to provide a verification of our work. We envision that this work may sharpen the understanding of $PT$-symmetric structures and inspire more acoustic functional devices.

Introducing porosity with different degrees of disorder has been widely used to regulate thermal properties of materials, which generally results in decrease of thermal conductivity. We investigate the thermal conductivity of porous metamaterials in the ballistic transport region by using the Lorentz gas model. It is found that the introduction of asymmetry and Gaussian disorder into porous metamaterials can lead to a strong enhancement of thermal conductivity. By dividing the transport process into ballistic transport, non-ballistic transport, and unsuccessful transport processes, we find that the enhancement of thermal conductivity originates from the significant increase ballistic transport ratio. The findings enhance the understanding of ballistic thermal transport in porous materials and may facilitate designs of high-performance porous thermal metamaterials.

Predicting thermal conductance of complex networks poses a formidable challenge in the field of materials science and engineering. This challenge arises due to the intricate interplay between the parameters of network structure and thermal conductance, encompassing connectivity, network topology, network geometry, node inhomogeneity, and others. Our understanding of how these parameters specifically influence heat transfer performance remains limited. Deep learning offers a promising approach for addressing such complex problems. We find that the well-established convolutional neural network models AlexNet can predict the thermal conductance of complex network efficiently. Our approach further optimizes the calculation efficiency by reducing the image recognition in consideration that the thermal transfer is inherently encoded within the Laplacian matrix. Intriguingly, our findings reveal that adopting a simpler convolutional neural network architecture can achieve a comparable prediction accuracy while requiring less computational time. This result facilitates a more efficient solution for predicting the thermal conductance of complex networks and serves as a reference for machine learning algorithm in related domains.

Auxetic two-dimensional (2D) materials, known from their negative Poisson's ratios (NPRs), exhibit the unique property of expanding (contracting) longitudinally while being laterally stretched (compressed), contrary to typical materials. These materials offer improved mechanical characteristics and hold great potential for applications in nanoscale devices such as sensors, electronic skins, and tissue engineering. Despite their promising attributes, the availability of 2D materials with NPRs is limited, as most 2D layered materials possess positive Poisson's ratios. In this study, we employ first-principles high-throughput calculations to systematically explore Poisson's ratios of 40 commonly used 2D monolayer materials, along with various bilayer structures. Our investigation reveals that BP, GeS and GeSe exhibit out-of-plane NPRs due to their hinge-like puckered structures. For 1T-type transition metal dichalcogenides such as $MX_{2}$ ($M$ = Mo, W; $X$ = S, Se, Te) and transition metal selenides/halides the auxetic behavior stems from a combination of geometric and electronic structural factors. Notably, our findings unveil V$_{2}$O$_{5}$ as a novel material with out-of-plane NPR. This behavior arises primarily from the outward movement of the outermost oxygen atoms triggered by the relaxation of strain energy under uniaxial tensile strain along one of the in-plane directions. Furthermore, our computations demonstrate that Poisson's ratio can be tuned by varying the bilayer structure with distinct stacking modes attributed to interlayer coupling disparities. These results not only furnish valuable insights into designing 2D materials with a controllable NPR but also introduce V$_{2}$O$_{5}$ as an exciting addition to the realm of auxetic 2D materials, holding promise for diverse nanoscale applications.

Metalenses, which may effectively manipulate the wavefront of incident light, have been proposed and extensively utilized in the development of various planar optical devices for specialized purposes. However, similar to traditional lenses, the metalens suffers from chromatic aberration problems due to the significant phase dispersion in each unit structure and the limited operational bandwidth. To mitigate the impact of chromatic aberration, we integrate a phase compensation approach with a novel utilization of a phase shift function to define the adjusted phase criterion satisfied by each $\alpha$-Si resonance unit. This approach may lead to development of an innovative optical tweezer known as an achromatic optical vortex metalens (AOVM), offering reliable focusing capabilities across the $1300$ nm and $1600$ nm incident light range. Numerical simulations are conducted to investigate the optical properties of $200$ nm diameter SiO$_{2}$ particles at the focal plane of the AOVM. The trapping ability of the AOVM is successfully validated, exhibiting favorable characteristics including constant optical force, stable kinematic state of trapped particles, and consistent capture positions, surpassing those of the optical vortex metalens.

Nonlinear optical properties are investigated using the static and time-resolved second harmonic generation in the topological material molybdenum phosphide (MoP) with three-component fermions. Giant second harmonic generation signals are detected and the derived $\chi^{(2)}$ value is larger than that of the typical electro–optic material. Upon optical excitation, no photoinduced change of the symmetry is detected in MoP, which is quite different from previous observations in several other topological materials.

High-order harmonics are ideal probes to resolve the attosecond dynamics of strong-field recollision processes. An easy-to-implement phase mask is utilized to covert the Gaussian beam to TEM01 transverse electromagnetic mode, allowing the realization of two-source interferometry of high-order harmonics. We experimentally measure the intensity dependence of dipole phase directly with high-order harmonic interferometry, in which the driving laser intensity can be precisely adjusted. The classical electron excursion simulations reproduce the experimental findings quite well, demonstrating that Coulomb potential plays subtle roles on movement of electrons for harmonics near the ionization threshold. This work is of great importance for precision measurements of ultrafast dynamics in strong-field physics.

Fiber laser is a fundamental component of laser systems and is of great significance for development of laser technology. Its pulse output can be divided into $Q$-switched and mode-locked. Achieving ultrashort pulse with narrower pulse duration and higher power is the focus of current research on mode-locked lasers. As an important component of fiber laser systems, saturable absorber (SA) can modulate losses in the optical cavity and generate pulses, enabling the laser system to achieve pulse output under long-term normal operating conditions better. Therefore, expanding the selection range of materials with better saturable absorption properties to improve the quality of pulse output is an important topic in current research. Here, the second generation topological insulator Bi$_{2}$Te$_{3}$ single crystal is prepared, and a ring fiber laser system is built with the Bi$_{2}$Te$_{3}$ SA. The mode-locked pulse with a pulse duration of 288 fs and a signal-to-noise ratio of 80.202 dB is realized. This result verifies that Bi$_{2}$Te$_{3}$, as a member of topological insulator, has good saturable absorption characteristics, and has broad prospects for the application research in lasers.

Based on the many-body radiative heat transfer theory, we investigate a thermal splitter based on three magneto-optical InSb nanoparticles. The system comprises a source with adjustable parameters and two drains with fixed parameters. By leveraging the temperature and magnetic field dependence of the permittivity of InSb, the direction of heat flux in the system can be controlled by adjusting the magnetic field or temperature at the source. Under magnetic field control, the coupling between the separated modes, and the suppression of the zero-field mode induced by the magnetic field, are utilized to achieve a thermal splitting ratio within the modulation range of 0.15–0.58. Furthermore, temperature control results in a thermal splitting ratio ranging from $0.15$ to $0.99$, as a result of the suppression of the zero-field mode by the magnetic field and the blue shift effect of the zero-field mode frequency increasing with temperature. Notably, the gap distance between nanoparticles does not significantly affect the splitting ratio. These findings provide valuable theoretical guidance for utilizing magneto-optical nanoparticles as thermal splitters and lay the groundwork for implementing complex heat flux networks using InSb for energy collection and heat transfer control.

The increasing demands for electronic devices to achieve high miniaturization, functional integration, and wide bandwidth will exacerbate the heat generation and electromagnetic interference, which hinders the further development of electronic devices. Therefore, both the issues of microwave absorption and heat dissipation of materials need to be addressed simultaneously. Herein, a multifunctional composite material is proposed by periodic arrangement of copper pillars in a matrix, based on the wave-absorbing material. As a result, the equivalent thermal conductivity of the composite structure is nearly 35 times higher than the wave-absorbing matrix, with the area filling proportion of the thermal conductivity material being 3.14%. Meanwhile, the reflectivity of the composite structure merely changes from $-15.05$ dB to $-13.70$ dB. It is proved that the designed composite structure possesses both high thermal conduction and strong microwave absorption. The measured results accord well with the simulation results, which demonstrates that the thermal conductivity of the composite structure can reach more than 10 W$\cdot$m$^{-1}\cdot$K$^{-1}$ without significant deterioration of the absorption performance.

Phonon lasers, as a novel kind of lasers for generating coherent sound oscillation, has attracted extensive attention. Here, we theoretically propose a nonreciprocal phonon laser in a hybrid optomechanical system, which is composed of an asymmetric Fabry–Pérot cavity, an ensemble of $N$ identical two-level atoms, and a mechanical oscillator. The effective driving amplitude related to driving direction leads to an obvious difference in mechanical gain and threshold power, bringing about a nonreciprocal phonon laser. In addition, the dependence of the phonon laser on the atomic parameters is also discussed, including the decay rate of the atoms and the coupling strength between the atoms and the cavity field, which provides an additional degree of freedom to control the phonon laser action. Our work provides a path to realizing a phonon laser in an atoms-cavity optomechanical system and may aid the manufacture of directional coherent phonon sources.

A thermal cloak is well known for hiding objects from thermal signature. A bilayer thermal cloak made from inner insulation layer and outer isotropic homogeneous layer could realize such thermal protection. However, its thermal protection performance can be suppressed for low-thermal-conductivity surrounding media. We propose a tri-layer thermal cloak model by adding a transition layer between the insulation layer and the outer layer. Numerical simulations and theoretical analysis show that, under the same geometry size and surrounding thermal conductivity, the performance of the thermal cloak can be significantly enhanced by introducing a transition layer with higher thermal conductivity and an outer-layer with lower thermal conductivity. The tri-layer cloak proposed provides a design guidance to realize better thermal protection using isotropic bulk materials.

Thermal metamaterials offer a promising avenue for creating artificial materials with unconventional physical properties, such as thermal cloak, concentrator, rotator, and illusion. However, designs and fabrication of thermal metamaterials are of challenge due to the limitations of existing methods on anisotropic material properties. We propose an evolutionary framework for designing thermal metamaterials using genetic algorithm optimization. Our approach encodes unit cells with different thermal conductivities and performs global optimization using the evolution-inspired operators. We further fabricate the thermal functional cells using 3D printing and verify their thermal illusion functionality experimentally. Our study introduces a new design paradigm for advanced thermal metamaterials that can manipulate heat flows robustly and realize functional thermal metadevices without anisotropic thermal conductivity. Our approach can be easily applied to fabrications in various fields such as thermal management and thermal sensing.

Thermal cloaks offer the potential to conceal internal objects from detection or to prevent thermal shock by controlling external heat flow. However, most conventional natural materials lack the desired flexibility and versatility required for on-demand thermal manipulation. We propose a solution in the form of homogeneous multilayer thermodynamic cloaks. Through an ingenious design, these cloaks achieve exceptional and extreme parameters, enabling the distribution of multiple materials in space. We first investigate the effects of important design parameters on the thermal shielding effectiveness of conventional thermal cloaks. Subsequently, we introduce an autonomous tuning function for the thermodynamic cloak, accomplished by leveraging two phase transition materials as thermal conductive layers. Remarkably, this tuning function does not require any energy input. Finite element analysis results demonstrate a significant reduction in the temperature gradient inside the thermal cloak compared to the surrounding background. This reduction indicates the cloak's remarkable ability to manipulate the spatial thermal field. Furthermore, the utilization of materials undergoing phase transition leads to an increase in thermal conductivity, enabling the cloak to achieve the opposite variation of the temperature field between the object region and the background. This means that, while the temperature gradient within the cloak decreases, the temperature gradient in the background increases. This work addresses a compelling and crucial challenge in the realm of thermal metamaterials, i.e., autonomous tuning of the thermal field without energy input. Such an achievement is currently unattainable with existing natural materials. This study establishes the groundwork for the application of thermal metamaterials in thermodynamic cloaks, with potential extensions into thermal energy harvesting, thermal camouflage, and thermoelectric conversion devices. By harnessing phonons, our findings provide an unprecedented and practical approach to flexibly implementing thermal cloaks and manipulating heat flow.

Metamaterial absorbers with carbon fiber reinforced polymer (CFRP) substrates, which are called meta-CFRPs, have recently gained recognition for their excellent mechanical and electromagnetic performance. Different from traditional metamaterial absorbers with an isotropic substrate, meta-CFRPs with a highly anisotropic CFRP substrate are facing challenges in acquiring polarization-insensitive absorption. Here, a lay-up-oriented structure design method is proposed to solve this problem. Considering the lay-up configuration of CFRP laminates, metallic patterns are designed under corresponding polarization angles and then united together to form an integral structure. A meta-CFRP with a typical CFRP lay-up configuration([0$^{\circ}/45^{\circ}/90^{\circ}/-45^{\circ}$]$_{3s}$) is designed and tested. The experimental results exhibit over 99% microwave absorptivity at 2.44 GHz for all polarization angles. The maximum shift among the resonance peaks of the curves at all polarization angles is only 0.021 GHz. Further studies show that when there are cross-ply laminates in the first few layers of the CFRP substrate, the lay-up-oriented design method can be effectively simplified by ignoring the subsequent lay-up orientations after the first cross-ply layers. Our method can not only provide an effective way for acquiring polarization-insensitive microwave response on meta-CFRPs but also be expected to be promoted to metamaterial absorbers with other anisotropic materials.

Chirp-rate-tunable microwave waveforms (CTMWs) with dynamically tunable parameters are of basic interest to many practical applications. Recently, photonic generation of microwave signals has made their bandwidths wider and more convenient for optical fiber transmission. An all-optical method for generation of multiband CTMWs is proposed and demonstrated on all-fiber architecture, relying on dual temporal cavity solitons with agile repetition rate. In the experiment, the triangular optical chirp microwave waveforms with bandwidth above 0.45 GHz (ranging from 1.45 GHz to 1.9 GHz) are obtained, and the chirp rate reaches 0.9 GHz/ms. The reconfigurability is also demonstrated by adjusting the control signal. This all-optical approach provides a technical basis for compact, multi-band reconfigurable microwave photonics transmission and reception systems.