Electrically tunable phase-change metasurface for dynamic infrared thermal camouflage

Dynamic infrared thermal camouflage technology has attracted extensive attention due to its ability to thermally conceal targets in various environmental backgrounds by tuning thermal emission.The use of phase change materials(PCMs)offers numerous advantages,including zero static power,rapid modulation rate,and large emissivity tuning range.However,existing PCM solutions still encounter several practical application challenges,such as temperature uniformity,amorphization achievement,and adaptability to different environments.In this paper,we present the design of an electrically controlled metal-insulator-metal thermal emitter based on a PCM metasurface,and numerically investigate its emissivity tunability,physical mechanisms,heat conduction,and thermal camouflage performance across different backgrounds.Furthermore,the influence of the quench rate on amorphization was studied to provide a guidance for evaluating and optimizing device structures.Simulation results reveal that the thermal emitter exhibits a wide spectral emissivity tuning range between 8 and 14μm,considerable quench rates for achieving amorphization,and the ability to provide thermal camouflage across a wide background temperature range.Therefore,it is anticipated that this contribution will promote the development of PCM-based thermal emitters for practical dynamic infrared thermal camouflage technology with broad applications in both civilian and military domains.

Nd-doped structurally disordered YSr_(3)(PO_(4))_(3) single crystal:Growth and laser performances

Disordered-structure crystals have drawn increasing attention as promising ultrashort laser material hosts owing to their broad linewidth.Herein,a novel disordered Nd:YSr_(3)(PO_(4))_(3)(Nd:YSP)crystal with good quality was successfully grown via the Czochralski pulling technique.The absorption and fluorescence spectra of the Nd:YSP single crystal were recorded at ambient temperature.The maximum absorption cross section for Nd:YSP single crystal is found to be approximately 3.89×10^(-20) cm^(2).The stimulated emission cross section for Nd:YSP crystal at~1060 nm was determined to be 7.64×10^(20) cm^(2) with the full width half maximum value of 22 nm.The fluorescence lifetime of the Nd3+ions in the Nd:YSP crystal is fitted to be 288μs.Diode-pumped continuous-wave laser operation is firstly realized at approximately 1060 nm.The maximum output power value from the Nd:YSP crystal is 714 mW,corresponding to a slope efficiency of-12.8%.The results indicate that the Nd:YSP crystal with a disordered structure may be a promising disordered laser host.

Systematic error suppression scheme of the weak equivalence principle test by dual atom interferometers in space based on spectral correlation

Systematic error suppression and test data processing are very important in improving the accuracy and sensitivity of the atom interferometer(AI)-based weak-equivalence-principle(WEP) test in space. Here we present a spectrum correlation method to investigate the test data of the AI-based WEP test in space by analyzing the characteristics of systematic errors and noises. The power spectrum of the Eotvos coefficient η, systematic errors, and noises in AI-based WEP test in space are analyzed and calculated in detail. By using the method, the WEP violation signal is modulated from direct current(DC) frequency band to alternating current(AC) frequency band. We find that the signal can be effectively extracted and the influence of systematic errors can be greatly suppressed by analyzing the power spectrum of the test data when the spacecraft is in an inertial pointing mode. Furthermore, the relation between the Eotvos coefficient η and the number of measurements is obtained under certain simulated parameters. This method will be useful for both isotopic and nonisotopic AI-based WEP tests in space.

Interference properties of a trapped atom interferometer in two asymmetric optical dipole traps

We investigate interference properties of a trapped atom interferometer where two symmetric optical dipole traps(ODTs)act as the atomic wave-packets splitter and combiner with internal state labelling.After the preparation of initial superposition states,the atomic wave-packet is adiabatically split and moves into two spatially separate asymmetric ODTs.The atomic wave-packets in two ODTs are then adiabatically recombined after a duration of free evolving in traps,completing the interference cycle of this atom interferometer.We show that the interferogram exhibits a series of periodic revivals in interference visibility.Furthermore,the revival period decreases as the asymmetry of two dipole potentials increases.By introducing an echo sequence to the interferometer,we show that while the echo effect is not influenced by the asymmetry of the two ODTs,the onset of periodic revivals changes by the echo sequence.Our study provides an effective method to cancel or compensate the phase shift caused by position and time correlated force.

Electro-elastic features of YBa3(PO_(4))3 and YbBa3(PO_(4))3 crystals with pure face-shear mode for acoustic wave sensor applications

The fundamental shear horizontal(SH0)waves have been proved to be a very useful method for nondestructive testing due to their non-dispersive characteristics.Currently,although several methods have been proposed to generate SH0 waves,it is still a challenge to obtain pure SH0 wave mode efficiently.Herein,in this study,non-centrosymmetric YBa3(PO_(4))3(YBP)and YbBa3(PO_(4))3(YbBP)crystals with pure face-shear mode were grown via the traditional Czochralski pulling method at temperatures above 1800℃.High resolution X-ray diffraction was carried out to evaluate the crystalline quality.Results showed that the YBP and YbBP crystals were of good quality,with the full width at half-maxima being on the order of 42.500 and 52.300,respectively.Moreover,the full set of electro-elastic constants for the YBP and YbBP crystals were determined and collated using a combination of impedance and pulse-echo methods.The piezoelectric coefficient(d14)of the YBP and YbBP crystals were determined to be 10.6 pC/N and 11.4 pC/N,respectively,corresponding to the electromechanical coupling coefficient(k14)equal to 15.4%and 15.9%,exhibiting large and pure face-shear vibration mode.Collectively,these results indicate that the YBP and YbBP crystals are promising for acoustic wave sensing application.

Beam-focused SH wave transducer based on YSr_(3)(PO_(4))_(3)piezoelectric crystal for high temperature structural health monitoring

Guided-wave-based structural health monitoring(SHM)technology is of great importance for real-time inspection of high-temperature structures.The fundamental shear horizontal(SH_(0))wave is believed to be an ideal wave mode for developing SHM systems due to its nondispersive characteristics.However,currently very limited SH_(0)wave transducers can be used for SHM of high-temperature structures due to the limitation of materials.Herein,a novel YSr_(3)(PO_(4))_(3)(YSP)piezoelectric crystal in the space group I43d was grown.Experiments show that the face-shear piezoelectric coefficient d_(14)(d_(14)=d_(25)=d_(36))is 9.7 pC/N and varies little from 25 to 800℃.Then a beam-focused SH_(0)wave piezoelectric transducer is developed based on face-shear-mode YSP wafers.Both finite element simulations and experimental results indicate that the YSP-based transducer can excite pure SH_(0)wave and focus the wave energy along two opposite main directions.Especially,the obtained SH_(0)wave beam is highly concentrated with a small divergence angle of less than 30°,originating from the high working frequency range from 300 to 400 kHz.The excellent temperature stability of the as-grown YSP crystal makes the proposed SH_(0)wave piezoelectric transducer very suitable for SHM of high-temperature structures.

Exploitable magnetic anisotropy and half-metallicity controls in multiferroic van der Waals heterostructure

Two-dimensional(2D)XY ferromagnets have drawn pronounced interest in recent years,but the characteristic of easy-plane magnetization restricts their application in spintronics to some extent.Here,we propose a general strategy for constructing multiferroic van der Waals heterostructures,aiming to achieve electrical control over the magnetic anisotropy in 2D XY ferromagnets.The validity of this strategy is verified by the heterostructure composed of ferromagnetic VBi_(2)Te_(4) and ferroelectric In_(2)Se_(3) monolayers.By manipulating the polarized states of In_(2)Se_(3),the VBi_(2)Te_(4) can be reversibly transformed between 2D XY and Heisenberg ferromagnets,characterized by the switching of easy magnetization axis between in-plane and out-of-plane directions.More interestingly,accompanied by the changes in magnetic anisotropy,the VBi_(2)Te_(4) also demonstrates a phase transition from a semiconductor to a half-metal state,which can be ascribed to the band alignment and interfacial charge transfer.The switchable magnetic and electronic properties enable the heterostructure to be utilized in nonvolatile memory and logic devices.Additionally,the half-metallicity and magnetocrystalline anisotropy energy of the heterostructure can be effectively tuned by biaxial strain.These findings not only pave the way for electrically nonvolatile control of 2D XY ferromagnet,but also facilitate the development of interfacial magnetoelectric physics and applications.

2,000,000 fps 2D and 3D imaging of periodic or reproducible scenes with single-pixel detectors

Single-pixel imaging(SPI)can capture 2D images of the target with only a nonpixelated detector,showing promising application potential in nonvisible spectral imaging,low-photon imaging,lidar,and other extreme imaging fields.However,the imaging mechanism of traditional SPI makes it difficult to achieve high imaging speed,which is a primary barrier for its widespread application.To address this issue,in this work,we propose and demonstrate a novel high-speed 2D and 3D imaging scheme based on traditional SPI,termed time-resolved single-pixel imaging(TRSPI).Previous SPI works mainly utilize correlation between a stable target and iterative illumination masks to reconstruct a single image.In TRSPI,by further exploiting correlation information between a dynamic scene and every static mask,we can reconstruct a series of time-varying images of the dynamic scene,given the dynamic scene is repetitive or reproducible.Experimentally,we conducted 2D and 3D imaging on a rotating chopper with a speed of 4800 revolutions per minute(rpm),and imaging speeds up to 2,000,000 fps.It is believed that this technology not only opens up a novel application direction for SPI,but also will provide a powerful solution for high-speed imaging.

Hybrid level anharmonicity and interference-induced photon blockade in a two-qubit cavity QED system with dipole–dipole interaction

We theoretically study a quantum destructive interference (QDI)-induced photon blockade in a two-qubit driven cavity quantum electrodynamics system with dipole–dipole interaction (DDI). In the absence of dipole–dipole interaction,we show that a QDI-induced photon blockade can be achieved only when the qubit resonance frequency is different from the cavity mode frequency. When DDI is introduced the condition for this photon blockade is strongly dependent upon the pump field frequency,and yet is insensitive to the qubit–cavity coupling strength. Using this tunability feature we show that the conventional energy-level-anharmonicity-induced photon blockade and this DDI-based QDI-induced photon blockade can be combined together,resulting in a hybrid system with substantially improved mean photon number and second-order correlation function. Our proposal provides a nonconventional and experimentally feasible platform for generating single photons.

Abnormal lattice occupation of Mo and related polarons in LiNbO_(3): Hybrid density functional theory investigation

Studies have reported that Mo-doped LiNbO_(3) exhibits excellent photorefractive performance,which may be attributed to the Mo abnormally occupation in Nb sites(MoNb)and the MoNb photorefractive centres.Therefore,we investigate the basic characteristics of Mo-doped LiNbO_(3),including the preferable substitutional sites,doping stability,lattice relaxation,and electronic structures using the spin-polarised density functional theory within semi-local and hybrid functionals.Particularly,the type and properties of the polarons in Mo-doped LiNbO_(3) are studied intensively,and the advantages of MoNb polarons with respect to the MoLi polarons are highlighted.The calculation results of both transfer energies and defect formation energies show that MoNb are preferable to be formed in both stoichiometric and congruent LiNbO_(3),while Mo substitutional Li(MoLi)is consumed in small amounts.MoNb could act as small bound polarons that exhibit fast response to light with respect to the MoLi bound bipolarons.The introduced double-centre by Mo doping is partly responsible for the excellent photorefractive properties of Mo-doped LiNbO_(3).

Generation of 12th order harmonic mode-locking in a Nd-doped single-mode all-fiber laser operating at 0.9μm

Based on the Nd-doped single-mode fiber as the gain medium,an all-fiber 12th harmonic mode-locked(HML)laser operating at the 0.9μm waveband was obtained for the first time,to the best of our knowledge.A mandrel with a diameter of 10 mm was employed to introduce bending losses to suppress mode competition at 1.06μm,which resulted in a suppression ratio of up to 54 dB.The 1st–12th order HML pulses with the tunable repetition rate of 494.62 kHz–5.94 MHz were obtained in the mode-locked laser with a center wavelength of∼904 nm.In addition,the laser has an extremely low threshold pump power of 88 mW.To the best of our knowledge,this is the first time that an HML pulse has been achieved in a 0.9μm Nd-doped single-mode all-fiber mode-locked laser with the advantages of low cost,simple structure,and compactness,which could be an ideal light source for two-photon microscopy.

Beam quality improvement of the high-energy KTA-OPO based on a confocal unstable cavity with Gaussian reflectivity mirror

A high-energy 100-Hz optical parametric oscillator(OPO)based on a confocal unstable resonator with a Gaussian reflectivity mirror was demonstrated.A KTA-based OPO with a good beam quality was obtained when the magnification factor was 1.5,corresponding to the maximum signal(1.53μm)energy of 56 m J and idler(3.47μm)energy of 20 m J,respectively.The beam quality factors(M^(2))were measured to be M^(2)_(x)=5.7,M^(2)_(y)=5.9 for signal and M^(2)_(x)=8.4,M^(2)_(y)=8.1 for idler accordingly.The experimental results indicated that the beam quality positively changed with the increase of magnification factors,accompanied by an acceptable loss of pulse energy.

Investigations on beam quality improvement of an NCPM-KTA-based high energy optical parametric oscillator using an unstable resonator with a Gaussian reflectivity mirror

Beam quality improvements by a large margin for signal and idler beams of a high energy 100 Hz KTiOAsO_(4)(KTA)non-critical phase matching(NCPM)optical parametric oscillator(OPO)were demonstrated using an unstable resonator configuration instead of a plane-parallel one.Theoretically,influences of cavity lengths and transmission of an output coupler on the OPO conversion efficiency for both were numerically simulated.For OPO based on an unstable resonator with a Gaussian reflectivity mirror,the maximum pulse energies at the signal(1.53μm)and idler(3.47μm)were about 75 mJ and 26 mJ,respectively.The corresponding beam quality factors of the signal were M_(x)^(2)=9.8 and M_(y)^(2)=9.9,and M_(x)^(2)=11.2 and M_(y)^(2)=11.5 for the idler.As a comparison,128 mJ of signal and 48 mJ of idler were obtained with the plane-parallel resonator,and the M~2 factors of the signal were M_(x)^(2)=39.8 and M_(y)^(2)=38.4,and M_(x)^(2)=32.1 and M_(y)^(2)=31.4 for the idler.Compared with a plane-parallel cavity,over eight times and three times brightness improvements were realized for the signal and idler light,respectively.

Switchable half-metallicity in A-type antiferromagnetic NiI_(2)bilayer coupled with ferroelectric In_(2)Se_(3)

Electrically controlled half-metallicity in antiferromagnets is of great significance for both fundamental research and practical application.Here,by constructing van der Waals heterostructures composed of two-dimensional(2D)A-type antiferromagnetic NiI_(2)bilayer(bi-NiI_(2))and ferroelectric In_(2)Se_(3)with different thickness,we propose that the half-metallicity is realizable and switchable in the bi-NiI_(2)proximate to In_(2)Se_(3)bilayer(bi-In_(2)Se_(3)).The polarization flipping of the bi-In_(2)Se_(3)successfully drives transition between half-metal and semiconductor for the bi-NiI_(2).This intriguing phenomenon is attributed to the joint effect of polarization field-induced energy band shift and interfacial charge transfer.Besides,the easy magnetization axis of the bi-NiI_(2)is also dependent on the polarization direction of the bi-In_(2)Se_(3).The half-metallicity and magnetic anisotropy energy of the bi-NiI_(2)in heterostructure can be effectively manipulated by strain.These findings provide not only a feasible strategy to achieve and control half-metallicity in 2D antiferromagnets,but also a promising candidate to design advanced nanodevices.

Mechanism Studies on the Degradation of Hexachlorocyclopentadiene in the Atmosphere

Hexachlorocyclopentadiene(HCCP) is one of the chlorinated and highly reactive pollutants, which can be released into the atmosphere and undergo chemical transformations. In this paper, the initiated reaction mechanisms of HCCP with typical atmospheric oxidants(·NO3, ·HO2, ·OH, and O3) were theoretically investigated. The results mean that all initiated reactions are exothermic, and the energy barriers do not exceed 16 kcal×mol-1. The rate constants of HCCP reaction triggered by ·NO3, ·HO2, ·OH, and O3 are 2.49 × 10-12, 2.44 × 10-22, 2.46 × 10-13 and 1.33 × 10-20 cm3×molecule-1×s-1 at 298 K, respectively. It can be concluded that the reaction of ·NO3 and ·OH with HCCP more likely occurs according to the rate constants. Then the subsequent reactions of the ·NO3/·OH-initiated intermediates with O2 and NO were calculated, resulting in that the cyclopentadiene is ruptured completely. And the results show that the Criegee intermediates created in the ozonization reactions of HCCP can react with O2, NO2 and SO2. This study gives more insight into the chemical transformation mechanisms of HCCP in the atmosphere.