Vortex splitting is one of the main causes of instability in orbital angular momentum (OAM) modes transmission. Recent advances in OAM modes free-space propagation have demonstrated that abruptly autofocusing Airy vortex beams (AAVBs) can potentially mitigate the vortex splitting effect. However, different modes of vortex embedding will affect the intensity gradients of the background beams, leading to changes in the propagation characteristics of vortex beams. This study presents the unification of two common methods of coupling autofocusing Airy beams with vortices by introducing a parameter (m), which also controls the intensity gradients and focusing properties of the AAVBs. We demonstrate that vortex splitting can be effectively reduced by selecting an appropriate value of the parameter (m) according to different turbulence conditions. In this manner, the performance of OAM-based free-space optical systems can be improved.

Average transmittance of multi-Gaussian (flat-topped and annular) optical beams in an anisotropic turbulent ocean is examined analytically based on the extended Huygens–Fresnel principle. Transmittance variations depending on the link length, anisotropy factor, salinity and temperature contribution factor, source size, beam flatness order of flat-topped beam, Kolmogorov microscale length, rate of dissipation of turbulent kinetic energy, rate of dissipation of the mean squared temperature, and thickness of annular beam are examined. Results show that all these parameters have effects in various forms on the average transmittance in an anisotropic turbulent ocean. Hence, the performance of optical wireless communication systems can be improved by taking into account the variation of average transmittance versus the above parameters.

We experimentally demonstrate an underwater optical wireless power transfer (OWPT) using a laser diode (LD) as a power transmitter. We investigate the characteristics of a solar cell and a photodiode (PD) as a power receiver. We optimize the LD, the PD, and the solar cell to achieve the maximum transfer efficiency. The maximum transfer efficiency of the back-to-back OWPT is measured as 4.3% with the PD receiver. Subsequently, we demonstrate the OWPT in tap and sea water. Our result shows an attenuation of 3 dB/m in sea water.

A 52 m/9 Gb/s four-level pulse amplitude modulation (PAM4) plastic optical fiber (POF)-underwater wireless laser transmission (UWLT) convergence with a laser beam reducer is proposed. A 52 m/9 Gb/s PAM4 POF-UWLT convergence is practically demonstrated with the application of a laser beam reducer to reduce the collimated beam diameter. A 50 m graded-index (GI)-POF is employed as an underwater extender to efficiently enhance the coverage of UWLT. The performances of PAM4 POF-UWLT convergence in view of bit error rate (BER) and eye diagrams improve with the decrease of the collimated beam diameter because of the small amount of light absorbed by clear ocean water. Competent BER and eye diagrams (three independent eye diagrams) are achieved over a 50 m GI-POF transmission with a 2 m clear ocean water link.

The average bit-error-rate (BER) performance is studied for a coherent free-space optical communication system employing differentially encoded quadrature phase-shift keying (QPSK) with the Mth-power phase estimation method. A closed-form expression, considering the combined effects of the Málaga (M) turbulence fading, pointing errors, and phase estimation errors, is derived in terms of Meijer’s G function. Numerical and Monte Carlo simulation results are presented to verify the derived expression.

The Cramer–Rao lower bound on range error is modeled for pseudo-random ranging systems using Geiger-mode avalanche photodiodes. The theoretical results are shown to agree with the Monte Carlo simulation, satisfying boundary evaluations. Experimental tests prove that range errors caused by the fluctuation of the number of photon counts in the laser echo pulse leads to the range drift of the time point spread function. The function relationship between the range error and the photon counting ratio is determined by using numerical fitting. Range errors due to a different echo energy is calibrated so that the corrected range root mean square error is improved to 1 cm.

As an extension of the Mie lidar technique to measure the extinction coefficient of the surface particles, a horizontally pointing Mie lidar is used for determining the optical properties of Asian dust, which is an approach without knowing the actual lidar ratio. A long lasting dust event is observed based on this approach in May 2014. The “no dust,” “pure dust,” and “polluted dust” stage is observed during this event, and their optical and hygroscopic properties are discussed. Some new optical and hygroscopic features are observed, which benefit from the quantitative, multi-wavelength, and continuous measurement of the extinction related optical properties of dust particles.

We develop a regularization-based algorithm for reconstructing the Cn2 profile using the profile of Fried’s transverse coherent length (r0) of differential column image motion (DCIM) lidar. This algorithm consists of fitting the set of measured data to a spline function and a two-stage inversion method based on regularized least squares QR-factorization (LSQR) in combination with an adaptive selection method. The performance of this algorithm is analyzed by a simulated profile generated from the HV5/7 model and experimental DCIM lidar data. Both the simulation and experiment support the presented approach. It is shown that the algorithm can be applied to estimate a reliable Cn2 profile from DCIM lidar.

Mathematical models for the superimposed orbital angular momentum (OAM) mode of multiple Hankel–Bessel (HB) beams in anisotropic non-Kolmogorov turbulence are developed. The effects of anisotropic turbulence and source parameters on the mode detection spectrum of the superimposed OAM mode are analyzed. Anisotropic characteristics of the turbulence in the free atmosphere can enhance the performance of OAM-based communication. The HB beam is a good source for mitigating the turbulence effects due to its nondiffraction and self-focusing properties. Turbulence effects on the superimposed OAM mode can be effectively reduced by the appropriate allocation of OAM modes at the transmitter based on the reciprocal features of the mode cross talk.

Analytical formulas for a class of tunable random electromagnetic beams propagating in a turbulent atmosphere through a complex optical system are derived with the help of a tensor method. One finds that the far field intensity distribution is tunable by modulating the source correlation structure function. The on-axis spectral degree of polarization monotonically increases to the same value for different values of order M in free space while it returns to the initial value after propagating a sufficient distance in turbulence. Furthermore, it is revealed that the state of polarization is closely determined by the initial correlation structure rather than by the turbulence parameters.

A mobile vehicle lidar system has been developed and applied to detect urban air quality. On September 21 and 22, 2015, particulate matter observation with mobile vehicle lidar was carried out in the Binhai New Area of Tianjin. Combined with the latitude and longitude information acquired by a GPS, the three-dimensional distribution of the aerosol extinction coefficient was presented in the experimental area. Furthermore, the source, distribution, and the transportation path of the aerosols in the area were investigated based on lidar data, local meteorological data, and backward trajectory analysis. The results show that mobile vehicle lidar can detect the atmospheric aerosols and reflect the stereoscopic distribution properties of aerosols. The potential of this vehicle lidar system provides a new scientific basis for the study of the source, distribution, and transportation of atmospheric particles.

A zonal decoupling algorithm used to control a dual deformable mirror (DM) is proposed. One of the two DMs is characterized with a large stroke (woofer), while the other one is characterized by a high spatial frequency (tweeter). A numerical model is used to compare the zonal decoupling algorithm with some traditional zonal decoupling algorithms. The simulation results indicate that the algorithm presented in this Letter improves the performance in suppressing the coupling error. An experimental system is built to prove the effectiveness of this algorithm. The experiments demonstrate that the phase aberrations could be effectively compensated and that the coupling error could also be suppressed.

A prototype of a solar ground-layer adaptive optics (GLAO) system, which consists of a multi-direction correlating Shack–Hartmann wavefront sensor with 30 effective subapertures and about a 1 arcmin field of view (FoV) in each subaperture, a deformable mirror with 151 actuators conjugated to the telescope entrance pupil, and a custom-built real-time controller based on field-programmable gate array and multi-core digital signal processor (DSP), is implemented at the 1 m New Vacuum Solar Telescope at Fuxian Solar Observatory and saw its first light on January 12th, 2016. The on-sky observational results show that the solar image is apparently improved in the whole FoV over 1 arcmin with the GLAO correction.

Our adaptive optics system based on a non-modulation pyramid wavefront sensor is integrated into a 1.8 m astronomical telescope installed at the Yunnan Observatory in LiJiang, and the first light with high-resolution imaging of an astronomical star is successfully achieved. In this Letter, the structure and performance of this system are introduced briefly, and then the observation results of star imaging are reported to show that the angular resolution of an adaptive optics system using a non-modulation pyramid wavefront sensor can approach the diffraction limit quality of a 1.8 m telescope.

The average bit error rate (BER) performance of a free-space optical (FOS) system based on the multi-hop parallel decode-and-forward cooperative communication method with an M-ary phase shift keying subcarrier intensity modulation is studied systematically. With the max–min criterion as the best path selection scheme, the probability density function and the cumulative distribution function of the gamma–gamma distribution random variable signal-to-noise ratio are derived. The analytical BER expression is then obtained in terms of the Gauss–Laguerre quadrature rule. Monte Carlo simulation is also provided to confirm the validity of the presented average BER model.

A second generation solar adaptive optics (AO) system is built and installed at the 1-m New Vacuum Solar Telescope (NVST) of the Fuxian Solar Observatory (FSO) in 2015. The AO high-order correction system consists of a 151-element deformable mirror (DM), a correlating Shack–Hartmann (SH) wavefront sensor (WFS) with a 3500 Hz frame rate, and a real-time controller. The system saw first light on Mar. 16, 2015. The simultaneous high-resolution photosphere and chromosphere images with AO are obtained. The on-sky observational results show that the contrast and resolution of the images are apparently improved after the wavefront correction by AO.

We simulate the integrated effects of atmospheric aberration, atmospheric turbulence, thermal blooming, random jitter of laser's intensity and phase, speed of wind, direction of wind, absorption of air, kinetic cooling of CO2 and N2, speed of target, output power and beam quality of laser, wavelength, focus length, and the launch altitude of laser to accurately simulate the transmission loss of the laser's energy, concentration of laser's power and other beam quality parameters of the laser propagating to the dynamic target. And we evaluate the efficiency of laser's irradiation on the target more accurately for the optical link of ground-to-airspace. We also investigate influences of characteristics of dynamic parameters (Strehl's ratio, RMS of wave-front, spatial distribution of intensity on the target, the real focus on the optical link and the peak intensity along the propagation path) including speed of wind, direction of wind, speed of target and the kinetic cooling effect of air, especially. We conclude that the higher speed of wind and target weakens the thermal blooming of atmosphere and improves the beam quality and efficiency of laser's irradiation on the target. The kinetic cooling effect of air is more remarkable to improve the beam quality irradiating on the target at the initial part of the propagation path of the laser. The changed direction of wind weakens the atmospheric aberration and directs to better beam quality and higher efficiency of laser's irradiation on the target.

Partially coherent vortex beams are generated by the illumination of high-power red-color light-emitting diodes. We investigate the influence of correlation property of partially coherent vortex beams on intensity distribution. The correlation property of partially coherent vortex beams are modulated by adjusting the propagation distance of the incident light. Effects of the topological charge and propagation distance of vortex beams on the intensity are also studied. Experiment results are consistent with theoretical simulations.

In this Letter, we investigate the packet error rate (PER) performance of digital pulse interval modulation (DPIM) for free-space optical (FSO) links under the combined effect of turbulence and pointing errors. The theoretical model is developed by considering the effect of some important parameters, including turbulence condition, beamwidth, receiver aperture size, jitter variance, data rate, transmitted optical power, etc. A closed-form average PER expression for DPIM is derived for this fading channel. The results of numerical simulation are further provided to verify the validation of our model. This work can be helpful for selecting DPIM in the FSO system design.

We establish a system to measure the functional absorption cross section of photosystem II (PSII) (\sigma PSII) and maximum quantum yield of photochemistry in PSII (Fv/Fm). The system utilizes a sequence of high-frequency excitation flashes at microsecond intervals to induce a microsecond-level fluorescence yield curve. Parameters \sigma PSII and Fv/Fm are calculated by fitting the curve using nonlinear regression. Experimental results show that the relative standard deviation (RSD) of the system is less than 3%, and the correlation coefficient of Fv/Fm values measured by this system and those measured by pulse amplitude modulation method is 0.950.

Remote measurements of Earth's surface from ground, airborne, and spaceborne instruments show that its albedo is highly variable and is sensitive to solar zenith angle (SZA) and atmospheric opacity. Using a vali-dated radiative transfer calculating toolbox, DISORT and a bidirectional reflectance distribution function library, AMBRALS, a land surface albedo (LSA) lookup table (LUT) is produced with respect to SZA and aerosol optical depth. With the LUT, spectral and broadband LSA can be obtained at any given illumination geometries and atmospheric conditions. It provides a fast and accurate way to simulate surface reflectance over large temporal and spatial scales for climate study.

In the letter the polarization properties of quasi-homogenous (QH) beam propagating in Kolmogorov and non-Kolmogorov turbulence are studied. The results show that the polarization properties of QH beam undergoes three stages during the propagation in turbulence: in the “near field”, the degree of polarization (Dop) and the state of polarization (Sop) fluctuate with source parameters and transverse position; after that the beam come to the “middle field” where its properties are affected by source parameters and turbulence perturbation; in the final “far field”, the values come to constants which dependent only on source parameters.

A closed-form bit-error rate (BER) expression is derived for free-space optical (FSO) communication systems with circle polarization shift keying and spatial diversity receivers in the gamma-gamma (GG) distribution fading channel. This model can predict the performance without the need of lengthy simulation runs. The performance can be analyzed by some system parameters such as atmospheric conditions, link length, communication wavelength, receiver aperture size, and number of spatial diversity receivers. Numerical results demonstrate the influence of the above parameters on the FSO systems and show quantitatively the differences in behavior among various different parameters.

We present an analysis of the impact of afluctuating-loss channel on free-space quantum key distribution (QKD). Considering the characteristics of the fluctuating-loss channel, a scintillation discriminator that acts according to the information of instant channel loss is proposed to help improve the performance of a free-space QKD system, which suffers from the influence of atmospheric turbulence. Theoretical and numerical results show that this discriminator is a useful tool for increasing secure key rates, especially for long-range free-space QKD.

A method on amplitude-weighted array technology is proposed based on an analytical formula in which the radiation amplitudes of array elements are evaluated analytically by a random symmetrical far-field radiation pattern. Using this formula, any desired spatial radiation pattern in the far field could be built by applying the analytical solutions of radiation amplitudes of array elements. To check the validity of this formula as well as the proposed technique, an annular intensity distribution as target far-field pattern is designed, and the respective radiation amplitude of array elements are determined by solving the formula analytically. The available far-field pattern is calculated by applying these solutions and then compared with the target far-field pattern. The theoretical results show the capabilities of the analytical derivation as well as the proposed technique in forming specific radiation patterns.

Orthogonal polynomials over the interior of a unit circle are widely used in aberration theory and in describing ocular wavefront in ophthalmic applications. In optics, Zernike polynomials (ZPs) are commonly applied for the same purpose, and scaling their expansion coefficients to arbitrary aperture sizes is a useful technique to analyze systems with different pupil sizes. By employing the orthogonal Fourier–Mellin polynomials and their properties, a new formula is established based on the same techniques used to develop the scaled pupil sizes. The description by the orthogonal Fourier–Mellin polynomials for the aberration functions is better than that by the ZPs in terms of the wavefront reconstruction errors.

We propose and experimentally evaluate a novel approach to measure atmospheric turbulence, in which imaging of light column technology is integrated into a differential motion method. In the approach, a large acquisition scene of the light column and a narrow field of view of one pixel of the charge-coupled device respectively allow high temporal and spatial resolutions, which offer the possibility of path-integrated turbulence strength measurement with multiple paths. In addition, we describe the measurement principle of the approach. Lastly, comparative experiment is performed to verify the feasibility of the approach.

Analytical expressions of the temporal power spectral models of angle of arrival (AOA) fluctuations are derived using the generalized exponential spectral model for optical waves propagating through weak non-Kolmogorov turbulence. Compared with expressions of temporal power spectral models derived from the general non-Kolmogorov spectral model, the new expressions consider the influences of the inner and outer scales of finite turbulence. Numerical calculations show that large outer scales of turbulence increase the value of the temporal power spectrum of AOA fluctuations in low-frequency regions.

The fastness and robustness of a control algorithm are highly important in the performance of adaptive optics systems. The proportional-integral-derivative control with arranging the transient process, which is designed using a tracking differentiator, is applied into an adaptive optics system. This control algorithm greatly improves the dynamic properties of the control system. To identify the underlying reasons for these improvements, the influence of the control algorithm is theoretically discussed. The control algorithm is verified by a simple adaptive optics system for tip/tilt correction. The experimental results demonstrate that the control algorithm is fast and robust.

An approach for determining cirrus height with multiple scattering effect using data from a Mie scattering lidar is proposed. We compute the exact extinction coefficients of cirrus via altitude. The regulated height of cirrus is obtained through multiple scattering factors. Experimental result demonstrates that the proposed approach can be used to determine effectively cirrus height with multiple scattering.

The optical data which collected in situ in inshore and offshore of Daya Bay in July 26, 2 010 is presented. The data is collected by using the instrument, which synchronously measured the volume scattering function in seven directions from 20o to 160o, the attenuation coefficient, and the depth of water. The analysis of the data indicates that in Daya Bay, in general, the scattering and attenuation increase with depths after 4 m below the surface, while it decreases with depths from near surface layer to 4 m. But not for the area near Daya Bay Nuclear Power Station due to the unique geographical environment of it.

We present the numerical simulation and analysis of the bandwidth estimation for adaptive optics (AO) systems based on stochastic parallel gradient descent (SPGD) optimization. Time-varying atmosphere turbulence due to wind velocity and turbulence structure constant is considered in the dynamic simulation. The performance of SPGD system with different iteration frequencies is studied in detail. A formula given that estimates the Strehl ratio degradation after SPGD adaptive control due to the increasing proportion of the number of deformable mirror actuator times Greenwood frequency to iteration frequency based on numerical analyses, can be used to roughly predict the required iteration frequency under the condition of various Greenwood frequencies.

A combined Raman/elastic backscatter lidar observations is carried out in the Pearl River Delta (PRD) China. The results show the largest lidar ratios of the order of 80 sr in the uplifting boundary layer in 2-3 km during the haze period. In the moderate pollution period, the lidar ratio has an average value of 58 sr. The Angstrom exponent exhibits high values around 1.82, indicating the presence of rather small particles. Different back air mass trajectories and the ambient atmospheric conditions are attributed to the distinct characteristics of aerosol optical properties in the haze and moderate pollution episodes. In the lower layer in the haze period, air masses are mostly advected from southeast coast China. In contrast, the air mass in the moderate pollution observing period passes through northwest China, indicating the combination of some pollution from the Tarim Basin in case of strong convection and the smoke from adjacent fire burning spot in PRD region.

Chemical warfare agents (CWAs) are recognized as serious threats of terrorist acts against the civilian population. Minimizing the impact of these threats requires early detection of the presence of CWAs. Cavity ring-down spectroscopy (CRDS) is an exquisitely sensitive technique for the detection of trace gaseous species. In this letter, the CRDS technique is employed using a pulsed quantum cascade laser for the detection of dimethyl methylphosphonate (DMMP). A limit of DMMP detection of approximately 77 ppb is achieved. The best achievable sensitivity that corresponds to noise-equivalent absorption is approximately 2 \times 10-7cm-1.

A three-wavelength lidar system is set up. The backscatter signals of 355, 532, and 1 064 nm are measured simultaneously to derive the optical depth, lidar ratio, and backscatter color ratio of cirrus clouds, respectively. The lidar configuration and the data processing are described. The case study shows that the optical depths of cirrus clouds are not dependent on wavelength while the backscatter color ratios are.

We propose the use of a power pulse shape of the widely known optical soliton, corresponding to the hyperbolic secant square function, for both conventional atmospheric optical communication systems and, especially, for new full-optical wireless communications. We analyze the performance of the proposed pulse in terms of peak-to-average optical power ratio (PAOPR) and bit error rate (BER). During the analysis, we compare the proposed pulse shape against conventional rectangular and Gaussian pulse shapes with reduced duty cycle. Results show the noticeable superiority of the proposed pulse for atmospheric optical links.

The equivalence of the modulation transfer function (MTF) of a turbid medium and the transmitted radiance from the medium under isotropic diffuse illumination is demonstrated. MTF of a turbid medium can be fully evaluated by numerically solving a radiative transfer problem in a plane parallel medium. MTF for a homogenous single layer turbid medium is investigated as illustration. General features of the MTF in the low and high spatial frequency domains are provided through their dependence on optical thickness, single scattering albedo, asymmetrical factor, and phase function type.

A real-time method for measuring atmospheric parameters based on co-processor field-programmable gate array (FPGA) and main processor digital signal processing (DSP) is proposed for ground-based telescopes with adaptive optics (AO) systems. Coherence length, outer scale, average wind speed, and coherence time are estimated according to closed-loop data on the residual slopes and the corrected voltages of AO systems. This letter introduces the principle and architecture design of the proposed method, which is successfully applied in the 127-element AO system of the 1.8-m telescope of Yunnan Astronomical Observatory. The method enables real-time atmospheric observations with the same object and path of the AO system. This method is also applicable to extended objects.

Exo-atmospheric targets are especially difficult to distinguish using currently available techniques, because all target parts follow the same spatial trajectory. The feasibility of distinguishing multiple type components of exo-atmospheric targets is demonstrated by applying the probabilistic neural network. Differences in thermal behavior and time-varying signals of space-objects are analyzed during the selection of features used as inputs of the neural network. A novel multi-colorimetric technology is introduced to measure precisely the temporal evolutional characteristics of temperature and emissivity-area products. To test the effectiveness of the recognition algorithm, the results obtained from a set of synthetic multispectral data set are presented and discussed. These results indicate that the discrimination algorithm can obtain a remarkable success rate.

Using the US National Aeronautics and space Administration (NASA) Earth Observing-1 Mission (EO-1) hyperion hyperspectral remote sensing data, we study the shallow-water bathymetry inversion in Smith Island Bay. The fast line-of-sight atmospheric analysis of spectral hypercubes module is applied for atmo-spheric correction, and principal component analysis method combined with scatter diagram and maximum likelihood classification is used for seabed classification. The diffuse attenuation coefficient Kd is derived using quasi-analytical algorithm (QAA), which performs well in optically deep water. Kd obtained from QAA requires correction, particularly those derived in some coastal areas with optically shallow water and calculated by direct inversion based on radiative transfer theory to obtain the bathymetry. The direct inversion method derives the water depth quickly, and matches the results from optimized algorithm.

A method of interference correction for improving the sensitivity of non-dispersive infrared (NDIR) gas analysis system is demonstrated. Based on the proposed method, the interference due to water vapor and carbon dioxide in the NDIR NO analyzer is corrected. After interference correction, the absorbance signal at the NO filter channel is only controlled by the absorption of NO, and the sensitivity of the analyzer is improved greatly. In the field experiment for pollution source emission monitoring, the concentration trend of NO monitored by NDIR analyzer is in good agreement with the differential optical absorption spectroscopy NO analyzer. Small variations of NO concentration can also be resolved, and the measuring correlation coefficient of the two analyzers is 94.28%.

Although the empirical mode decomposition (EMD) method is an effective tool for noise reduction in lidar signals, evaluating the effectiveness of the denoising method is difficult. A dual-field-of-view lidar for observing atmospheric aerosols is described. The backscattering signals obtained from two channels have different signal-to-noise ratios (SNRs). The performance of noise reduction can be investigated by comparing the high SNR signal and the denoised low SNR signal without a simulation experiment. With this approach, the signal and noise are extracted to one intrinsic mode function (IMF) by the EMD-based denoising; thus, the threshold method is applied to the IMFs. Experimental results show that the improved threshold method can effectively perform noise reduction while preserving useful sudden-change information.

A new method to count the expected value and variance of time dispersion is presented for time dispersion of underwater optical wireless communication. Instead of the typically used Gamma distribution, inverse-Gaussian distribution is suggested for underwater optical impulse response time waveform function. The expectation of this method is in good agreement with experimental data. Future works may include water absorption to the model.

The description of a plane wave diffracted by a circular aperture is directly started from the Maxwell's equations. Based on the vector angular spectrum representation of Maxwell's equations, the diffracted plane wave is decomposed into the TE and TM terms. The analytical TE and TM terms in the far field are presented by stationary phase. As the TE and TM terms are orthogonal to each other in the far field, their sum constitutes the so-called Airy disc pattern. Therefore, this research reveals the composition of Airy disc, which is beneficial to deepen and enhance the recognition of the classical diffraction problem.

The influence of organic contamination in vacuum on the laser-induced damage threshold (LIDT) of coatings is studied. TiO2/SiO2 dielectric mirrors with high reflection at 1064 nm are deposited by the electronbeam evaporation method and their LIDTs are measured in vacuum and atmosphere, respectively. It is found that the contamination in vacuum is easily attracted to optical surfaces because of the low pressure and becomes the source of damage, O2 molecules in vacuum with contamination can accelerate the laser-induced damage by observing LIDT and damage morphologies. LIDTs of mirrors have a little change in vacuum compared with in atmosphere when the organic contamination is wiped off. The results indicate that organic contamination is a significant reason to decrease the LIDT in vacuum.

Adaptive optics (AO) technique has been extensively used for large ground-based optical telescopes to overcome the effect of atmospheric turbulence. But the correction is often partial. An iterative blind deconvolution (IBD) algorithm based on maximum-likelihood (ML) method is proposed to restore the details of the object image corrected by AO. IBD algorithm and the procedure are briefly introduced and the experiment results are presented. The results show that IBD algorithm is efficient for the restoration of some useful high-frequency of the image.

Based on the Rytov approximation and the cross-spectral density approximation for the mutual coherence function of the partially coherent field, the propagation properties of the partially coherent beams with optical vortices in turbulent atmosphere are discussed. The average intensity and the mutual coherence function of the partially coherent vortex beams propagation in weak turbulent atmosphere are obtained. It is shown that the vortex structure of the average cross-spectral density of partially coherent beams has the same helicoidally shape as that of the phase of the fully coherent Laguerre-Gauss beams in free space and the relative intensity of the beam is degraded by optical vortex.

Under the approximations of (1) the received irradiance fluctuations of an optical wave caused by small scale turbulent eddies are multiplicatively modulated by the fluctuations caused by large scale turbulent eddies; (2) the scintillations caused by small- and large-scale eddies, respectively, are statistically independent; (3) the Rytov method for optical scintillation collected by the finite-diameter receiving aperture is valid for light wave propagation under weak to saturation fluctuation regime, we develop the applicable aperture-averaging analytic formulas in the week-to-strong-fluctuation for the scintillations of plane and spherical waves, which include the outer- and inner-scale rules of turbulence.

A phase singularity of the light field created by interference of two Gaussian singular beams which propagate in a weak and near ground turbulent atmosphere is analyzed by the Rytov approximation and the short-term averaging method of the dislocation-position. We demonstrate that an edge or circular dislocation may be formed by both parallel and coaxial or noncoaxial collimated beams with different or equal beam-width interfere. The edge or circular short-term wavefront dislocations of super position field depend on the atmospheric turbulence strength, beam propagation distance, amplitude ratio, dislocation of nesting vortices, and beam-width or beam-width ratio of the individual beams.

Lidar is an efficienttool for remote monitoring, but the effective range is often limited by signal-to-noise ratio (SNR). By the power spectralestimation, we find that digital filters are not fit for processing lidar signals buried in noise. In this paper, we present a new method of the lidar signal acquisition based on the wavelet trimmed thresholding technique to increase the effective range of lidar measurements. The performance of our method is investigated by detecting the real signals in noise. Theexperiment results show that our approach is superior to the traditional methods such as Butterworth filter.

Based on Raman-shifted wavelengths of D2 and CH4 pumped by third harmonic of Nd:YAG laser, a differential absorption lidar was presented in this paper and had been constructed for probing environmental NO2 concentration. NO2 experimental measurements were carried out at Anhui Institute of Optics and Fine Mechanics in Hefei. Some NO2 measurement results were given and discussed.

L625 Raman lidar has been developed for water vapor measurements over Hefei, China since September 2000. By transmitting laser beam of frequency-tripled Nd:YAG laser, Raman scattering signals of water vapor and nitrogen molecules are simultaneously detected by the cooled photomultipliers with photon counting mode. Water vapor mixing ratios measured by Raman lidar show the good agreements with radiosonde observations, which indicates this Raman lidar is reliable. Many observation cases show that aerosol optical parameters have the good correlation with water vapor distribution in the lower troposphere.

The significant variation of the laser output can be caused by feedback of a small part of laser beam, which is reflected or backscattered by a target at a long distance from laser source, into the laser cavity. This paper describes and analyzes theoretically and experimentally the influence of atmospheric turbulence on interference caused by laser feedback. The influence depends upon both the energy of feedback into the laser cavity and the strength of turbulence over a laser propagation path in the atmosphere. In the case of stronger energy of feedback and weak turbulence variance of fluctuation of the laser output can be enhanced by hundreds to thousands times. From our measurements and theoretical analysis it shows thatthese significant enhancements can result from the change of laser-cavity-modes which can be stimulated simultaneously and from beat oscillations between a variety of frequencies of laser modes. This also can result from optical chaos inside the laser resonator because a non-separable distorted external cavity can become a prerequisite for optical chaos.

It is reported that the wave-front aberration produced by atmosphere disturbance can be compensated with nonlinear optics phase conjugate technology. The distance of laser propagating in atmosphere is up to 1.27 km away. The result shows that SBS phase conjugating beam energy can be focus in a little area on target. And the biggest energy of phase conjugating beam on target is up to 142 mJ.

On the basis of Kolmogorov's theorem, the physical meanings of beams' correlation function on received plane are extended. Approximate formula of channels' across correlation coefficient is deduced from multiple beams through atmosphere. And the scintillation variance of multiple beams is also induced. The result shows along with the channels close to one another, the correlation coefficient increases, and so does the scintillation variance. When the channels completely combine, the scintillation variance of multiple channels is with no difference from that of one channel.