Generation of structured light beams with polarization variation along arbitrary spatial trajectories using tri-layer metasurfaces

Conventionally,the spatially structured light beams produced by metasurfaces primarily highlight the polarization modulation of the beams propagating along the optical axis or the beams'spatial transmission trajectory.In particular,along the optical axis,the polarization state is either constant or varies continuously in each output plane.Here,we develop innovative spatially structured light beams with continually changing polarization along any arbitrary spatial transmission trajectories.With tri-layer metallic metasurfaces,the geometric characteristics of each layer structure can be adjusted to modulate the phase and polarization state of the incident terahertz(THz)wave.The beam will converge to the predefined trajectory along several paths to generate a Bessel-like beam with longitudinal polarization changes.We demonstrate the versatility of the approach by designing two THz-band structured light beams with varying polarization states along the spatial helical transmission trajectory.Continuous linear polarization changes and linear polarization to right circular polarization(RCP)and back to linear polarization changes are realized respectively.The experimental results are basically consistent with the simulated results.Our proposal for arbitrary trajectory structured light beams with longitudinally varying polarization offers a practical method for continuously regulating the characteristics of spatial structured light beams with non-axial transmission.This technique has potential uses in optical encryption,particle manipulation,and biomedical imaging.

Highly efficient vectorial field manipulation using a transmitted tri-layer metasurface in the terahertz band

Polarization is a basic characteristic of electromagnetic waves that conveys much optical information owing to its many states.The polarization state is manipulated and controlled for optical information security,optical encryption,and optical communication.Metasurface devices provide a new way to manipulate wave-fronts of light.A single ultrathin metasurface device can generate and modulate several differently polarized light fields,and thus carries optical information in several different channels.Terahertz(THz)waves have become widely used as carrier waves for wireless communication.Compact and functional metasurface devices are in high demand for THz elements and systems.This paper proposes a tri-layer metallic THz metasurface for multi-channel polarization generation and phase modulation with a high efficiency of approximately 80%.An azimuthally polarized THz vectorial beam generator is realized and characterized for use as a THz polarization analyzer.The incident polarization angle can be observed graphically with high accuracy.Moreover,a vectorial hologram with eight channels for different linear polarization states is demonstrated experimentally.The information in different holograms can be hidden by choosing the polarization channel for detection.This work contributes to achieving multi-functional metasurface in the THz band and can benefit THz communication and optical information security.

Polarization multiplexing for double images display

Metasurface provides subwavelength structures for manipulating wavefronts of light. The benefits of subwavelength components offer a continuous modulation of amplitude, phase, and polarization, thus eliminating the production of higher-order images and improving the utilization of light intensity. Despite the rapid progress in this field, multiparameter control of light using single layer metasurface is rarely reported. In fact, multiparameter control of light helps to improve information storage capacity and image fidelity. With simultaneous manipulation of polarization and amplitude at each pixel, it is possible to encode two separate images into one metasurface and reconstruct them under proper conditions. In a proof of concept experiment, we demonstrate an independent display of two binary images at the same position with polarization de-multiplexing from a single metasurface. This unique technology of encoding two images through amplitude and polarization manipulation provides a new opportunity for various applications in, such as encryption, information storage, polarization holograms, optical communications and fundamental physics.

Conditional Diagnosability of the Locally Twisted Cubes under the PMC Model

In a multiprocessor systems, it is important to local and to replace the faulty processors to maintain systempsilas high reliability. The fault diagnosis, which is the process of identifying fault processors in a multiprocessor system through testing. The conditional diagnosis requires that for each processor u in a system, all the processors that are directly connected to u do not fail at the same time. In this paper, we study the conditional diagnosability of the n-dimensional locally twisted cubes. After showing some properties of the locally twisted cubes, we prove that it under the PMC model is 4n – 7 for n ≥ 5.

Terahertz generation from laser-induced plasma

Interest of the research in terahertz(THz)wave has been strongly motivated by its wide applications in the fields of physics,chemistry,biology,and engineering.Developing efficient and reliable THz source is of uttermost priority in these researches.Numerous attempts have been made in fulfilling the THz generation.Greatly benefited from the progress of the ultrafast pulses,the laser-induced-plasma is one of the auspicious tools to provide desirable THz waves,owing to its superiorities in high power threshold,intense THz signal,and ultrawide THz spectrum.This paper reviews the physics and progress of the THz generation from the laser-induced plasmas,which are produced by gas,liquid,and solid.The characteristics of the emitted THz waves are also included.There are many complicated physical processes involved in the interactions of laser-plasma,making various laser-plasma scenarios in the THz generations.In view of this,we will only focus on the THz generation classified by physical mechanisms.Finally,we discuss a perspective on the future of THz generation from the laser-induced plasma,as well as its involved challenges.

Application and Experience of Putting People First in Hospital Human Resource Management

The recent years have witnessed the rapid economic growth of our country.The medical industry has also come to a new era.The number of hospital staff continues to increase,while some problems of managing human resource have gradually emerged.These problems have a bad impact on the functions of the hospital.We must attach great importance to solve them.In the process of managing the human resources of hospital,we must insist to put people first.That is how we can better boost the working initiative of medical staff,setting the foundation for the development of hospital in a long run.This article has conducted deepening research on this issue.First of all,it briefly introduced the theory of putting people first.And then it stated the connotation of the theory of putting people first applied in managing human resources of hospital.At last,it explored the strategies on applying the theory of putting people first in managing human resources of hospital in accordance to the concrete conditions.

Distribution Characteristics of δ^(13) C during the Decomposition Process of Soil Organic Matters under Different Climates and in Different Vegetation Zones

[ Obiective] The research aims to study distribution characteristics of 613C during the decomposition process of soil organic matters under different climates and in different vegetation zones.[Method] This essay measures the values of δ^13Corg in vadous soil profiles from different climatic zones and vegetation zones in order to obtain the precise corrected value. The 14 profiles of the following soil types in different zones are collected： brown earths in arid and semi-arid regions covered by C3 forests, yellow earths in humid zone covered by shrubs and forest, sandy loess from arid area covered by sparse vegetation, Ioess-paleosols in arid and semi-arid regions covered by C3/C4 grassland, yellow soils and paleosols in semi humid regions covered by C3/C4 grassland and yellow earths in humid areas covered by C3/C4 grassland. The measurement of δ^3Corg and standardized testing of the organic carbon are carried with above-mentioned profiles. An unified and skewed trend is not observed in the variation of δ^3C values in these profiles. A discussion about the causes of distribution features is held in this essay. [Result] If the measurement of δ^3C in the organic matters of paleosols is adopted in order to precisely rebuild the historical vegetation cover, the kinetic fractionation should be taken into consideration to calculate the 6TM Corg in the prolife from the soils that is exclusively covered by C3 plants; the δ^3 Corg in the organic matters of the sand loess in the arid regions is affected by the contribution from basis; during the long-term decomposition of the organic matters in soils covered by C3/ C4 grassland, the range of δ^3Corg is under 2%. [ Conclusion] In view of the mixed vegetation cover, the profile distribution of δ^3Corg in different geographic periods is more likely to indicate the ratio of C4 plants to C3 plants.

Moire meta-device for flexibly controlled Bessel beam generation

High-order Bessel beams are of great interest for most stable long-range optical quantum communications due to their unique nondiffraction,self-healing,and orbital angular-momentum-carrying capabilities.Until now,metasurfaces based on Bessel beam generators are mostly static and focused on generating zero-order Bessel beams.A moirémeta-device made of two cascaded metasurfaces is a simple,effective strategy to dynamically manipulate the wavefront of electromagnetic(EM)waves by mutual rotation between the two metasurfaces.Here,an all-dielectric moirémeta-device integrated with the functions of an axicon and a spiral phase plate to generate terahertz Bessel beams is designed.Not only the order,but also the nondiffraction length of the generated Bessel beam can be continuously tuned.As a proof of concept of the feasibility of the platform,the case of tuning order is experimentally demonstrated.The experimental results are in good agreement with the theoretical expectations.In addition,we also numerically proved that the nondiffraction length of the Bessel beam can be adjusted with the same approach.The moirémeta-device platform is powerful in dynamically manipulating the wavefront of EM waves and provides an effective strategy for continuously controlling the properties of the Bessel beam,which may find applications in optical communications,particle manipulation,and super-resolution imaging.

Potential terahertz therapeutic strategy for the prevention or mitigation of Alzheimer’s disease pathology

With terahertz irradiation with a specific frequency,the fibrotic progression ofβ-amyloid oligomers is suppressed,which provides a potential therapeutic strategy for Alzheimer’s disease.

Hourly energy consumption characteristics of metro rail transit:Train traction versus station operation

The electricity consumption of the urban metro system can be mainly divided into the following two categories:the electricity consumption for train traction(E_(t))and the electricity consumption for station operation(E_(s)).Although understanding the hourly fluctuation characteristics of E_(t) and E_(s) contributes to renewable energy inte-gration and achieving carbon emission reduction of the metro system,the hourly fluctuation characteristics have been poorly reported in the literature.Thus,a typical underground non-transfer metro station of a city’s metro system in the North China Plain is selected in this study,and E_(t) and E_(s) were monitored to portray their hourly fluctuation characteristics.Results reveal that the hourly E_(t) shows a significant intraday“U”shape on weekdays,indicating two symmetric peaks in morning and evening rush hours.While the hourly E_(s) shows an intraday“flat”shape,indicating it is nearly free from the effect of rush hour.Moreover,it is statistically proved that the train frequency is the core influencing factor resulting in the intraday fluctuation of hourly E_(t).In the case study,when the train frequency increases from the mean(20 trains per hour)to maximum(32 trains per hour),the hourly E_(t) will increase by 53.4%.

Graphene-enabled electrically controlled terahertz meta-lens

Metasurfaces have become a new photonic structure for providing potential applications to develop integrated devices with small thickness, because they can introduce an abrupt phase change by arrays of scatterers. To be applied more widely, active metasurface devices are highly desired. Here, a tunable terahertz meta-lens whose focal length is able to be electrically tuned by ～4.45λ is demonstrated experimentally. The lens consists of a metallic metasurface and a monolayer graphene. Due to the dependence of the abrupt phase change of the metasurface on the graphene chemical potential, which can be modulated using an applied gate voltage, the focal length is changed from 10.46 to 12.24 mm when the gate voltage increases from 0 to 2.0 V. Experimental results are in good agreement with the theoretical hypothesis. This type of electrically controlled meta-lens could widen the application of terahertz technology.

Efficient manipulations of circularly polarized terahertz waves with transmissive metasurfaces

The unrestricted control of circularly polarized(CP)terahertz(THz)waves is important in science and applications,but conventional THz devices suffer from issues of bulky size and low efficiency.Although Pancharatnam-Berry(PB)metasurfaces have shown strong capabilities to control CP waves,transmission-mode PB devices realized in the THz regime are less efficient,limiting their applications in practice.Here,based on Jones matrix analysis,we design a trilayer structure(thickness of ~λ/5)and experimentally demonstrate that the structure can serve as a highly efficient transmissive meta-atom(relative efficiency of ~90%)to build PB metadevices for manipulating CP THz waves.Two ultrathin THz metadevices are fabricated and experimentally characterized with a z-scan THz imaging system.The first device can realize a photonic spin Hall effect with an experimentally demonstrated relative efficiency of ~90%,whereas the second device can generate a high-quality background-free CP Bessel beam with measured longitudinal and transverse field patterns that exhibit the nondiffracting characteristics of a Bessel beam.All the experimental results are in excellent agreement with full-wave simulations.Our results pave the way to freely manipulate CP THz beams,laying a solid basis for future applications such as biomolecular control and THz signal transportation.

Ambient formaldehyde concentrations in summer in 30 Chinese cities and impacts on air cleaning of built environment

Formaldehyde is an important carcinogen commonly found indoors.Its indoor sources have been intensively in-vestigated.But study on outdoor formaldehyde concentration,which is potentially an important source to indoors,remains scarce.This study attempts to characterize temporal and spatial distribution of the atmospheric formalde-hyde concentration in Chinese cities.Diurnal variation of ambient formaldehyde was examined in 6 cities and peak hours were identified between 12:00 pm and 3:00 pm.Consequently,outdoor formaldehyde concentrations were measured in the peak hours in 30 cities during the summer months of Jul.-Aug.,2022.The formaldehyde concentrations in the peak hours fell into a range of 0.005-0.087 mg/m^(3)(median value is 0.027 mg/m^(3)),87.7%of which have exceeded the chronic reference exposure criteria of 0.009 mg/m^(3) set by Office of Environmental Health Hazard Assessment.Health risk analysis suggests that exposure to ambient formaldehyde could cause a median carcinogenic risk of 1.9×10^(−5)(3.17×10^(−6)-6.13×10^(−5)),higher than threshold limit of 10−6.Pearson correlation analysis of the 30 cities shows that ambient summertime atmospheric formaldehyde concentrations of the city are positively correlated with its Gross Domestic Product(r=0.48).We also found that the outdoor formaldehyde concentrations in urban areas(median:0.017 mg/m^(3))is slightly higher than those in suburban areas(median:0.013 mg/m^(3)).Results here prove that outdoor formaldehyde is ubiquitous in Chinese cities and reduces effectiveness of ventilation in dilution indoor concentrations.Neglecting it would underestimate air cleaner capacity needed by a factor of about two.It should be accounted for in health analysis and air quality engineering control design of built environment in the future.