Numerical simulation of super-continuum laser propagation in turbulent atmosphere

Considering the atmospheric extinction and turbulence effects,we investigate the propagation performances of supercontinuum laser sources in atmospheric turbulence statistically by using the numerical simulation method,and the differences in propagation properties between the super-continuum(SC)laser and its pump laser are also analyzed.It is found that the propagation characteristics of super-continuum laser are almost similar to those of the pump laser.The degradation of source coherence degree may cause the relative beam spreading and scintillation indexes to decrease at different propagation distances or different turbulence strengths.The root-mean-square value of beam wandering is insensitive to the variation of source correlation length,and less aperture averaging occurs when the laser source becomes less coherent.Additionally,from the point of view of beam wandering,the SC laser has no advantage over the pump laser.Although the pump laser can bring about a bigger aperture average,the SC laser has a lower scintillation which may be due to the multiple wavelength homogenization effects on intensity fluctuations.This would be the most important virtue of the SC laser that can be utilized to improve the performance of laser engineering.

Revising the H_(2)^(16)O line-shape parameters around 1.1μm based on the speed-dependent Nelkin–Ghatak profile and the Hartmann–Tran profile

Accurate spectroscopic data for H_(2)^(16)O in the 1.1μm region are particularly important for the study of Earth's atmosphere.The pure water vapor molecular spectra were measured based on direct laser absorption spectroscopy using a narrow line-width external cavity diode laser combined with a high-precision Fabry-Pérot etalon.A total of 31 H_(2)^(16)O transitions were studied for the first time by using the speed-dependent Nelkin-Ghatak profile and the Hartmann-Tran profile.From an accurate line-shape analysis,we obtained the line intensities and the self-broadening coefficients,and they are compared with the available data reported in the HITRAN 2016 database and the HITRAN 2020 database.Finally,we obtained information on the influence of Dicke narrowing,as well as the correlations between Dicke narrowing and speed dependence,and of speed-dependent effects.

High-power xenon lamp-pumped Er:YAP pulse laser operated in free-running and acousto-optical Q-switching modes

We demonstrate a high-energy and high-power pulse laser on a xenon lamp-pumped Er:YAP crystal. The laser performance and thermal focal lengths under different working frequencies are discussed. The results show that the thermal lens effect is gradually aggravated with the increase of working frequencies, and even working at 100 Hz, a single pulse energy of 234 m J can be achieved. A maximum average power of 41.5 W is achieved with a working frequency of 20 Hz and slope efficiency of 2.82%. This output power is much higher than other xenon lamp-pumped erbium laser devices.A Q-switched laser is demonstrated by using the TeO2crystal, the maximum output energies of 11.5 m J and 3.5 m J are obtained at 50 and 100 Hz, the corresponding peak powers are 93.4 k W and 17.2 kW, respectively.The laser wavelengths and beam quality factors are also characterized in the free-running and Q-switched modes. A higher pulse energy and peak power laser could be achieved further by improving the damage threshold of TeO2acousto-optical Q-switching. All the experimental results illustrate that the xenon lamp-pumped Er:YAP laser is a promising candidate for high-power and high-frequency mid-infrared laser devices.

Efficient single-pixel imaging encrypted transmission based on 3D Arnold transformation

Single-pixel imaging(SPI)can transform 2D or 3D image data into 1D light signals,which offers promising prospects for image compression and transmission.However,during data communication these light signals in public channels will easily draw the attention of eavesdroppers.Here,we introduce an efficient encryption method for SPI data transmission that uses the 3D Arnold transformation to directly disrupt 1D single-pixel light signals and utilizes the elliptic curve encryption algorithm for key transmission.This encryption scheme immediately employs Hadamard patterns to illuminate the scene and then utilizes the 3D Arnold transformation to permutate the 1D light signal of single-pixel detection.Then the transformation parameters serve as the secret key,while the security of key exchange is guaranteed by an elliptic curve-based key exchange mechanism.Compared with existing encryption schemes,both computer simulations and optical experiments have been conducted to demonstrate that the proposed technique not only enhances the security of encryption but also eliminates the need for complicated pattern scrambling rules.Additionally,this approach solves the problem of secure key transmission,thus ensuring the security of information and the quality of the decrypted images.

Experimental damage thresholds of a laser suppression imaging system using a cubic phase plate

The development of laser systems leads to an increasing threat to photoelectric imaging sensors.A cubic phase plate wavefront coding imaging system is proposed to reduce the risk of damage owing to intense laser radiation.Based on the wavefront coding imaging model,the diffracted spot profile and the light intensity distribution on the observation plane are simulated.An experimental device is set up to measure the laser-induced damage thresholds and investigate the morphology of laser-induced damage patterns of the conventional and the wavefront encoding imaging system.Simulations and experimental results manifest the superior laser suppression performance of the proposed method,which can help diminish the undesirable effects of laser irradiation on an imaging sensor.

Upconversion luminescence and temperature sensing performance of Er^(3+) ions doped self-activated KYb(MoO_(4))_(2) phosphors

In this work,a series of self-activated KYb(MoO_(4))_(2) phosphors with various x at% Er^(3+) doping concentrations(x=0.5,1,3,5,8,10,15) was synthesized by the solid-state reaction method.The phase structure of the as-prepared samples was analyzed by X-ray diffraction(XRD),XRD Rietveld refinement and Fourier transform infrared(FT-IR) spectroscopy.The as-prepared samples retain the orthorhombic structure with space group of Pbcn even Er^(3+) doping concentration up to 15 at%.High-purity upconversion(UC) green emission with green to red intensity ratio of 55 is observed from the as-prepared samples upon the excitation of 980 nm semiconductor laser and the optimum doping concentration of Er^(3+) ions in the self-activated KYb(MoO_(4))_(2) host is revealed as 3 at%.The strong green UC emission is confirmed as a two-photon process based on the power-dependent UC spectra.In addition,the fluorescence intensity ratios(FIRs) of the two thermally-coupled energy levels,namely ^(2)H_(11/2) and ^(4)S_(3/2).of Er^(3+) ions were investigated in the temperature region 300-570 K to evaluate the optical temperature sensor behavior of the sample.The maximum relative sensitivity(S_(R)) is determined to be 0.0069 K^(-1) at300 K and the absolute sensitivity(S_(A)) is determined to be 0.0126 K^(-1) at 300 K.The S_(A) of self-activated KYb(MoO_(4))2:Er^(3+)is almost twice that of traditional KY(MoO_(4))2:Er^(3+)/Yb^(3+)codoping phosphor.The results demonstrate that Er^(3+) ions doped self-activated KYb(MoO_(4))2 phosphor has promising application in visible display,trademark security and optical temperature sensors.

Investigating the effect of volatility on the hygroscopicities of acetate nanoparticle aerosols by surface plasmon resonance microscopy

Under high relative humidity(RH)conditions,the release of volatile components(such as acetate)has a significant impact on the aerosol hygroscopicity.In this work,one surface plasmon resonance microscopy(SPRM)measurement system was introduced to determine the hygroscopic growth factors(GFs)of three acetate aerosols separately or mixed with glucose at different RHs.For Ca(CH_(3)COO)_(2) or Mg(CH_(3)COO)_(2) aerosols,the hygroscopic growth trend of each time was lower than that of the previous time in three cyclic humidification from 70% RH to 90% RH,which may be due to the volatility of acetic acid leading to the formation of insoluble hydroxide(Ca(OH)_(2) or Mg(OH)_(2))under high RH conditions.Then the third calculated GF(using the Zdanovskii-Stokes-Robinson method)for Ca(CH_(3)COO)_(2) or Mg(CH_(3)COO)_(2) in bicomponent aerosols with 1:1 mass ratio were 3.20% or 5.33% lower than that of the first calculated GF at 90% RH.The calculated results also showed that the hygroscopicity change of bicomponent aerosol was negatively correlated with glucose content,especially when the mass ratio of Mg(CH_(3)COO)_(2) to glucose was 1:2,the GF at 90% RH only decreased by4.67% after three cyclic humidification.Inductively coupled plasma atomic emission spectrum(ICP-AES)based measurements also indicated that the changes of Mg^(2+)concentration in bicomponent was lower than that of the single-component.The results of this study reveal thatduring the efflorescence transitions of atmospheric nanoparticles,the organic acids diffusion rate may be inhibited by the coating effect of neutral organic components,and the particles aging cycle will be prolonged.

Dynamic 3D holographic projection of vectorial images with a multimode fiber

An optical multimode fiber(MMF)is capable of delivering structured light modes or complex images with high flexibility.Here,we present a holographic approach to enable the MMF as a 3D holographic projector with the capability of complete polarization control.By harnessing the strong coupling of the spatial and polarization degrees of freedom of light propagating through MMFs,our approach realizes active control of the output intensity and polarization in 3D space by shaping only the wavefront of the incident light.In this manner,we demonstrate MMF-based holographic projection of vectorial images on multiple planes via a phase-only hologram.Particularly,dynamic projection of polarization-multiplexed grayscale images is presented with an averaged Pearson correlation coefficient of up to 0.91.Our work is expected to benefit fiber-based holographic displays,data transmission,optical imaging,and manipulation.

Laser-induced damage and periodic stripe structures of a CaF2 single crystal by an ArF excimer laser

The laser-induced damage threshold of a calcium fluoride(CaF2)single crystal was obtained by a 193 nm ArF excimer laser.The damage morphology of the crystal was analyzed.The results showed that the surface of CaF2 single crystal broke along the natural cleavage plane under ArF excimer laser irradiation,some fragments fell off,and Newton’s rings were observed on the curved fragments.Laser-induced periodic stripe structures(LIPSS)appeared on the surface layer beneath the fragments that peeled off.The spacing of LIPSS was measured,and the formation mechanism of LIPSS was analyzed based on the interference model.

Bacterial Cellulose Templated p-Co3O4/n-ZnO Nanocomposite with Excellent VOCs Response Performance

In this work,p-type Co3O4 decorated n-type ZnO(Co3O4/ZnO)nanocomposite was designed with the assistance of bacterial cellulose template.Phase composition,morphology and element distribution were investigated by XRD,SEM,HRTEM,EDS mapping and XPS.Volatile organic compounds(VOCs)sensing measurements indicated a noticeable improvement of response and decrease of working temperature for Co3O4/ZnO sensor,in comparison with pure ZnO,i.e.,the response towards 100 ppm acetone was 63.7(at a low working temperature of 180℃),which was 26 times higher than pure ZnO(response of 2.3 at 240℃).Excellent VOCs response characteristics could be ascribed to increased surface oxygen vacancy concentration(revealed by defect characterizations),catalytic activity of Co3O4 and the special p-n heterojunction structure,and bacterial cellulose provides a facile template for designing diverse functional heterojunctions for VOCs detection and other applications.

High-sensitivity methane monitoring based on quasi-fundamental mode matched continuous-wave cavity ring-down spectroscopy

Continuous-wave cavity ring-down spectroscopy(CW-CRDS)is an important technical means to monitor greenhouse gases in atmospheric environment.In this paper,a CW-CRDS system is built to meet the needs of atmospheric methane monitoring.The problem of mode matching is explained from the perspective of transverse mode and longitudinal mode,and the influence of laser injection efficiency on measurement precision is further analyzed.The results of cavity ring-down time measurement show that the measurement precision is higher when the laser is coupled with the fundamental mode.In the experiment,DFB laser is used to calibrate the system with standard methane concentration,and the measurement residual is less than±4×10^(-4)μs^(-1).The methane concentration in the air is monitored in real time for two days.The results show the consistency of the concentration changes over the two days,which further demonstrates the reliability of the system for the measurement of trace methane.By analyzing the influence of mode matching,it not only assists the adjustment of the optical path,but also further improves the sensitivity of the system measurement.

Analysis of extinction characteristics of non-spherical biological particle aggregates [Invited]

In this study,a method was presented to accurately obtain the extinction characteristics of the non-spherical biological particle aggregates.Based on the multi-sphere particle model of non-spherical particles,a randomly oriented aggregation model was firstly built to construct the aggregates.The discrete-dipole approximation method was used to calculate the extinction characteristics of aggregates in the 3–14 μm waveband.The average mass extinction coefficients of three materials are 0.802 m~2/g,0.907 m~2/g,and 0.866 m~2/g in the 3–5 μm waveband and 0.590 m~2/g,0.402 m~2/g,and 0.523 m~2/g in the8–14 μm band,respectively.Smoke chamber experimental results are in good agreement with theoretical analyses.

Plasmon-enhanced fluorescence of gold nanoparticle/graphene quantum dots for detection of Cr^(3+)ions

Graphene quantum dots(GQDs),fascinating semiconductors with stable photoluminescence(PL),have important potential applications in the fields of biology,medicine,and new semiconductor devices.However,it is still challenging to overcome the weak PL intensity.Here,we report a strategy for selective resonance enhancement of GQD fluorescence using gold nanoparticles(AuNPs)as plasmas.Interestingly,the addition of low concentration AuNP makes AuNP/GQDs exhibit significant fluorescence enhancement of 2.67 times in the visible range.The addition of high concentration AuNP leads to the formation of an excitation peak at 421 nm and selectively enhances certain radiation modes.We concluded that the main reason for the selective enhancement of PL intensity in high concentration AuNP is the transfer of generous hot electrons at high energy states from AuNP to GQD and relaxation to the ground state.The electron resonance of low concentration AuNP transfers to GQD and relaxes to lower energy levels,exhibiting an overall enhancement of PL intensity.We apply it for detection of the heavy metal ion Cr^(3+),and verify that it has a correlation coefficient of 97.36%.We believe AuNP/GQDs can be considered excellent candidates for heavy metal detection and high fluorescence bio-imaging.

Enhanced Photovoltage for Inverted Perovskite Solar Cells Using Delafossite CuCrO_(2) Hole Transport Material

Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)(PEDOT:PSS)has been widely adopted as hole transport material(HTM)in inverted perovskite solar cells(PSCs),due to high optical transparency,good mechanical flexibility,and high thermal stability;however,its acidity and hygroscopicity inevitably hamper the long-term stability of the PSCs and its energy level does not match well with perovskite materials with a relatively low open-circuit voltage.In this work,p-type delafossite CuCrO_(2)nanoparticles synthesized through hydrothermal method was employed as an alternative HTM for triple cation perovskite[(FAPbI_(3))_(0.87)(MAPbBr_(3))_(0.13)]_(0.92)(CsPbI_(3))_(0.08)(possessing better photovoltaic performance and stability than conventional CH3NH3PbI3)based inverted PSCs.The average open-circuit voltage of PSCs increases from 908 mV of the devices with PEDOT:PSS HTM to 1020 m V of the devices with CuCrO_(2)HTM.Ultraviolet photoemission spectroscopy demonstrates the energy band alignment between CuCrO_(2)and perovskite is better than that between PEDOT:PSS and perovskite,the electrochemical impedance spectroscopy indicates CuCrO_(2)-based PSCs exhibit larger recombination resistance and longer charge carrier lifetime than PEDOT:PSS-based PSCs,which contributes to the high VOCof CuCrO_(2)HTM-based PSCs.

Advances in coastal ocean boundary layer detection technology and equipment in China

Accurate and comprehensive knowledge of the atmospheric environment and its evolution within the coastal ocean boundary layer are necessary for understanding the sources,chemical mechanisms,and transport processes of air pollution in land,sea,and atmosphere.We present an overview of coastal ocean boundary layer detection technology and equipment in China and summarize the progress and main achievements in recent years.China has developed a series of coastal ocean boundary layer detection technologies,including Light Detection and Ranging(LIDAR),turbulent exchange analyzer,air-sea flux analyzer,stereoscopic remote sensing of air pollutants,and oceanic aerosol detection equipment to address the technical bottleneck caused by harsh environmental conditions in coastal ocean regions.Advances in these technologies and equipment have provided scientific assistance for addressing air pollution issues and understanding land-sea-atmosphere interactions over coastal ocean regions in China.In the future,routine atmospheric observations should cover the coastal ocean boundary layer of China.

Comparison of optical properties of bioaerosols composed of microbial spores and hyphae[Invited]

Bioaerosols exhibit significant broadband extinction performance and have vital impacts on climate change,optical detection,communication,disease transmission,and the development of optical attenuation materials.Microbial spores and microbial hyphae represent two primary forms of bioaerosol particles.However,a comprehensive investigation and comparison of their optical properties have not been conducted yet.In this paper,the spectra of spores and hyphae were tested,and the absorption peaks,component contents,and protein structural differences were compared.Accurate structural models were established,and the optical attenuation parameters were calculated.Aerosol chamber experiments were conducted to verify the optical attenuation performance of microbial spores and hyphae in the mid-infrared and far-infrared spectral bands.Results demonstrate that selecting spores and hyphae can significantly reduce the average transmittance from 21.2%to 6.4%in the mid-infrared band and from 31.3%to 19.6%in the far-infrared band within three minutes.The conclusions have significant implications for the selection of high-performance microbial optical attenuation materials as well as for the rapid detection of bioaerosol types in research on climate change and the spread of pathogenic aerosols.

Widely tunable and high resolution mid‑infrared laser based on BaGa_(4)Se_(7)optical parametric oscillator

The widely tunable and high resolution mid-infrared laser based on a BaGa_(4)Se_(7)(BGSe)optical parametric oscillator(OPO)was demonstrated.A wavelength tuning range of 2.76–4.64μm and a wavelength tuning resolution of about 0.3 nm were obtained by a BGSe(56.3°,0°)OPO,which was pumped by a 1064 nm laser.It is the narrowest reported wavelength tuning resolution for BGSe OPO,and was obtained by simultaneously controlling the angle and temperature of BGSe.

Upconversion luminescence and optical thermometry behaviors of Yb^(3+)and Ho^(3+)co‑doped GYTO crystal

Optical thermometry based on the upconversion(UC)luminescence intensity ratio(LIR)has attracted considerable attention because of its feasibility for achievement of accurate non-contact temperature measurement.Compared with traditional UC phosphors,optical thermometry based on UC single crystals can achieve faster response and higher sensitivity due to the stability and high thermal conductivity of the single crystals.In this study,a high-quality 5 at%Yb^(3+)and 1 at%Ho^(3+)co-doped Gd_(0.74)Y_(0.2)TaO_(4)single crystal was grown by the Czochralski(Cz)method,and the structure of the as-grown crystal was characterized.Importantly,the UC luminescent properties and optical thermometry behaviors of this crystal were revealed.Under 980 nm wavelength excitation,green and red UC luminescence lines at 550 and 650 nm and corresponding to the^(5)F_(4)/^(5)S_(2)→^(5)I_(8)and^(5)F_(5)→^(5)I_(8)transitions of Ho^(3+),respectively,were observed.The green and red UC emissions involved a two-photon mechanism,as evidenced by the analysis of power-dependent UC emission spectra.The temperature-dependent UC emission spectra were measured in the temperature range of 330–660 K to assess the optical temperature sensing behavior.At 660 K,the maximum relative sensing sensitivity(S_(r))was determined to be 0.0037 K^(−1).These results highlight the signifcant potential of Yb,Ho:GYTO single crystal for optical temperature sensors.

Wavefront detection performance analysis of plenoptic sensor

A numerical simulation model of plenoptic sensor aberration wavefront detection is established to simulate and analyze the detection performance of plenoptic sensor aberration wavefront for different turbulence intensities.The results show that the plenoptic sensor can achieve better distortion wavefront detection,and its wavefront detection accuracy improves with turbulence intensity.The unique optical structure design of the plenoptic sensor makes it more suitable for aberration wavefront detection in strong turbulent conditions.The wavefront detection performance of the plenoptic sensor is not only related to its wavefront reconstruction algorithm but also closely related to its structural parameter settings.The influence of structural parameters on the wavefront detection accuracy of plenoptic sensors under different turbulence intensities is simulated and analyzed.The variation law of wavefront detection accuracy and structural parameters under different turbulence intensities is summarized to provide a reference for the structural design and parameter optimization of plenoptic sensors.

Simultaneously detecting transversal and longitudinal displacement with the dielectric metasurface

The compact,sensitive,and multidimensional displacement measurement device plays a crucial role in semiconductor manufacture and high-resolution optical imaging.The metasurface offers a promising solution to develop high-precision displacement metrology.In this work,we proposed and experimentally demonstrated a two-dimensional displacement(XZ)measurement device by a dielectric metasurface.Both transversal and longitudinal displacements of the metasurface can be obtained by the analysis of the interference optical intensity that is generated by the deflected light beams while the metasurface is under linearly polarized incidence.We experimentally demonstrated that displacements down to 5.4 nm along the x-axis and 0.12μm along the z-axis can be resolved with a 900μm×900μm metasurface.Our work opens up new possibilities to develop a compact high-precision multidimensional displacement sensor.