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.

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.

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.

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.

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.

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.

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.

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.

Independent phase manipulation of co-and cross-polarizations with all-dielectric metasurface

Phase carried by two orthogonal polarizations can be manipulated independently by controlling both the geometric size and orientation of the dielectric nanopost.With this characteristic,we demonstrate a novel multifunctional metasurface,which converts part of the incident linearly polarized light into its cross-polarization and encodes the phase of the two orthogonal polarizations independently.A beam splitter and a bifocal metalens were realized in a single-layer dielectric metasurface by this approach.We fabricated the bifocal metalens and demonstrated that two focal spots in orthogonal polarizations can be separated transversely or longitudinally at will.The proposed approach shows a new route to design multifunctional metasurfaces with various applications in holography and three-dimensional display.

Temperature tuning of BaGa_(4)Se_(7) optical parametric oscillator

The temperature tuning of BaGa_(4)Se_(7)(BGSe)was demonstrated for the first time,to the best of our knowledge.When the temperature of BGSe(56.3°,0°)was raised from 30℃ to 140℃,the idler light under type Ⅰ raised from 3637 nm to 3989 nm,the tunable range reached 352 nm,and Δλ_(2)=ΔT reached 3.20 nm/℃.We calculated the phase matching curve of BGSe when Φ and T took different values.The relationship between θ and Δλ_(2)=ΔT was obtained by fixing Φ at 0°.The maximum Δλ_(2)=ΔT and its corresponding(θ,Φ)phase matching type were reported under different fixed λ_(2)(3μm,3.2μm,...,5μm).

Wide-field optical sizing of single nanoparticles with 10 nm accuracy

There is an increasing demand for new technologies to rapidly measure individual nanoparticles in situ for applications,including early-stage diagnosis of human diseases and environmental monitoring.Here,we demonstrate a label-free wide-field optical microscopy capable of sizing dispersed non-luminescent dielectric nanoparticles(with diameters down to 22 nm)with 10 nm accuracy.This technique utilizes enhanced nanoparticle-perturbed scattering by surface plasmons created on a gold film.In the meantime,an azimuthal rotation illumination module is installed on this microscope and a differential image processing technique is carried out.The relationship between the scattering intensity and the particle size was experimentally measured with good consistency with the theoretical prediction.The capability of precise measurement of the size of dispersed nanoparticles within a larger field of view in a label-free,non-invasive and quantitative manner may find broad applications involving single nanoparticle chemistry and physics.

Characteristics of the vertical structure of the atmospheric turbulence in the Tibetan Plateau

The Tibetan Plateau(TP)has unique atmospheric dynamics and thermal structures that originate from its giant terrain and complex climate.High vertical-resolution thermal radiosondes were launched near the central(Lhasa,91°06′E,29°36′N,3670 m above sea level(ASL))and marginal(Da Qaidam,95°21′E,37°51′N,3180 m ASL)areas of the TP during the summers of 2018 and 2020,respectively.Atmospheric turbulence parameters were calculated,and the characteristics of the atmospheric turbulent vertical structure at sunset in these two areas were analyzed and compared.Affected by TP thermal forcing and stably controlled by the summer monsoon anticyclone,the atmospheric refractive index structure constant(C_(n)^(2))tended to increase and then decrease with increasing height,reaching a maximum at the tropopause(~18 km ASL)at the Lhasa site.Although C_(n)^(2) at the Da Qaidam site also tended to increase at the tropopause,the position of the strong turbulent band(STB)(5–7 km ASL)was below the tropopause height corresponding to the potential temperature lapse rate minimum.The vertical distribution of C_(n)^(2) at the two sites,particularly regarding the position of the STB,was highly correlated with the atmospheric stability(Ri)and the thermal mixing scale(L_(T)).The significant correlations among the three parameters(STB,Ri,and L_(T))indicated that the strong fluctuations in temperature caused by thermal mixing were the dominant factor causing the Ri to be less than its critical value of 0.25.Moreover,the suppression strength involving the upward transport of the heat sources was the main reason for the different turbulent vertical structures and STB positions at the two sites.The zonal mean thermodynamic and dynamical fields derived from the reanalysis data also showed a height difference in the heat sources transported to the troposphere at the two sites.In the marginal TP,the material and energy in the lower troposphere were transported by the turbulent atmosphere upward along the slope of the mountain and converged at the central TP(28°N–35°N)with strong thermal forcing up to the tropopause.In the STB of the Lhasa site,the turbulent dissipation rate and eddy diffusion coefficient increased sharply,indicating that the turbulent atmosphere in this central site was highly diffused,and the small-scale turbulence transported the material and energy upward.