In general, the wavelength of the projected laser in a laser system is a bit different from the beacon wavelength used for target acquisition and tracking. So the dispersion influence of atmospheric refraction in the horizontal transmission path should be considered to reduce calibration errors of the optical axis. Firstly, the relationship between dispersion effect of horizontal atmospheric refraction and various practical parameters, such as vertical temperature gradient, vertical pressure gradient, laser wavelength and laser transmitting distance, is deduced by theoretical analysis. Then the calibration errors of optical axis caused by dispersion effect of horizontal atmospheric refraction in the near surface layer is also analyzed. Furthermore, atmospheric temperature and pressure of varying height are measured by means of two automatic meteorological stations. And the calculation results show that the dispersion effect of horizontal atmospheric refraction in the near surface layer for 1 km transmission could be about 3 μrad for 1 μm and 5 μm wavelengths, which would lead to calibration errors of about 1.5 μrad. It indicates that dispersion effect of horizontal atmospheric refraction in the near surface layer should be monitored in order to reduce theoptical axis calibration error, and the optical axis calibration should be carried out when dispersion effect is slight enough.

Coherence is an important property of laser beam, and laser beam with low spatial coherence is called partially coherent beam. Coherence structure is an unique parameter of partially coherent beams, and partially coherent beams with special coherence structure can be generated by manipulating their coherence properties. Partially coherent beams with special coherence structure not only exhibit many interesting propagation properties, but also can suppress the negative effects of atmospheric turbulence, such as degradation of intensity and coherence distribution, beam wander and scintillation, which have many application prospects in free-space optical communications, remote sensing, active laser radar systems, and so on. Recently, more and more attention is being paid to the propagation of partially coherent beams with special coherence structure in turbulent atmosphere. The research methods and development of partially coherent beams with special correlation structure are reviewed, and the propagation properties of partially coherent beams with Hermite series coherence structure in turbulent atmosphere are illustrated as examples.

High-resolution optical imaging of target has important application value in many optoelectronic engineering fields. However, in many target observation scenarios, light waves are transmitted through the atmosphere, which leads to the degradation of imaging quality. Obtaining high-quality images by overcoming complex atmospheric interference has always attracted the attention of international scholars. Especially in recent years, with the advancement of laser technology, due to the advantages of lidar in distance resolution and three-dimensional imaging, active imaging technology has also made great progress, in which the influence and correction of the atmosphere is also a problem that cannot be ignored. The impact of the atmosphere on imaging mainly includes two aspects: atmospheric turbulence and atmospheric suspended particles. Firstly, the impact of these two aspects on imaging is analyzed, and then some main techniques for eliminating atmosphericinfluences to obtain high-quality images are briefly introduced. At last, combined with long-term studies of the research group in related fields, several aspects that deserve attention are summarized and prospected.

To achieve a substantial retroreflection reduction accompanied with a superior anti-laser blinding property without suffering significant degradations in imaging quality, a novel defocused wavefront coding imaging system is designed. Relevant studies have been carried out around its mechanism in both anti-laser reconnaissance and anti-blinding. According to the Fresnel-Kirchhoff diffraction theory, the laser propagation through the defocused wavefront coding system is theoretically modeled. In this model, the transmission characteristics along with the laser defense performance are further evaluated, and the parameter optimization rules are proposed. Results show that by reducing the echo-detector receiving power and the maximum incident power per pixel by more than two and one order of magnitude respectively, the defocused wavefront coding system can greatly improve the performance of anti-laser reconnaissance and anti-blinding while maintaining good imaging quality.

The spatial resolution of the large ground-based optical telescope is far below its diffraction limitation because atmospheric turbulence distorts light waves from the observed space objects, which is a critical scientific and technological problem to be solved urgently. Using sodium beacon laser to excite sodium atoms in the upper atmosphere at an altitude of 80～105 km can create a high brightness sodium guide star, which can be used as a beacon to detect the wavefront aberration caused by atmospheric turbulence. As the wavefront aberration can be corrected by using adaptive optics system, the imaging resolution of large ground-based telescope will be significantly improved to be near its diffraction limitation. The development of sodium beacon laser is described in detail, especially the micro-second pulse sodium beacon laser with spectral format matched to the mesospheric D2 line developed in Research Center for Laser Physics and Technique, TechnicalInstitute of Physics and Chemistry, Chinese Academy of Sciences, as well as its successful application in some large ground-based optical telescopes.

Sodium guide star generated in sodium layer by 589 nm laser is considered as a critical component for ground-based optical telescope adaptive optical systems to correct the atmospheric aberrations of light transmission. Such kind of systems are of intense interest for applications in astronomical observations, ground-space optical communications and space debris tracking. Here, a novel sodium guide star laser based on diamond Raman technique is proposed and demonstrated. Output power scaling and single frequency operation are favored for the novel laser due to the high thermal conductivity of diamond crystal and the gain nature of the spatial hole burning-free. Recently, up to 22 W single mode diamond Raman laser at 589 nm had been demonstrated. Diamond Raman laser affords a highly efficient scheme for achieving high power sodium laser, and moreover, it is well suited to achieving microsecond pulsed, high repetition rate pulsed, and frequency chirped formats of interest for advanced sodium guide star laser systems.

Distributed holographic aperture digital imaging technology is an active imaging technology which uses digital holographic technology to record sub-aperture complex amplitude information, and then realizes comprehensive imaging through complex amplitude stitching between apertures. In engineering applications, it is well known that the assembly error of the imaging system will cause the shape and position errors between the sub-aperture complex amplitudes, and then blur the image after aperture synthesis. While in the existing methods, the shape and position errors are mostly corrected by the similar transformation model, but the relationship between the complex amplitude and ideal complex amplitude is complex projection transformation, so the method based on the similar transformation model is no longer applicable. Firstly, a method for correcting the shape and position errors between complex amplitudes on the image plane is proposed. In this method, projection transformation correction on the image plane complex amplitude is performed firstly through image registration, and then inverse Fresnel diffraction is performed on the corrected image plane complex amplitude to obtain the complex amplitude of the pupil plane corrected for shape and position errors. Then a distributed holographic aperture imaging system is built, and the shape and position errors are effectively corrected by correcting the shape and position errors between complex amplitudes on the image plane as suggested in this work.

When laser beam propagates through the strong turbulent atmosphere, phase vortex existing in the distorted wavefront makes the correction of adaptive optics system decline. By establishing a near ground laser propagation model, the distribution characteristics of phase vortex under different scintillation levels and the correction of adaptive optics system were analyzed. In order to investigate the reason why the phase vortex cannot be effectively corrected, the correction result of deformable mirrors with different number of actuators is analyzed when the wavefront distortion is completely restored. Results show that the adaptive optics system using the direct slope method can only correct the continuous phase, but not the discontinuous phase composed of phase vortices. And after the wavefront distortion with phase vortices is effectively restored, the continuous surface deformable mirror can correct the discontinuous phase. At this stage, the key factor limiting the correction effect of the adaptive optics is whether the wavefront distortion can be effectively restored.

The multi-angle scattering properties of atmospheric particles includes scattering function and scattering matrix (also known as “Müeller matrix"), which are not only the basic parameters for unpolarized and polarized radiative transfer simulation, but also the information carriers of the microphysical properties of atmospheric particles. Because of its fundamental position, how to obtain the scattering characteristics of aerosol has become an international hot spot of atmospheric research. The actuality and progress of the measurement techniques of the scattering function and Müeller matrix are reviewed, and the main content can be divided into four parts, as shown in the following: (1) Thechallenge and necessity of developing the measurement techniques of the multi-angle scattering properties are pointed out by analyzing the uncertainty of aerosol micro-physical properties and the limitation and complexity of the existed scattering theory. (2) The multi-angle scattering measurement techniques at visible-infrared band are described concisely, where the measurement instruments and prototypes of scattering function and Müeller matrix are grouped into three types according to their design principles, and the development progress, advantages and disadvantages of the different types of design are analyzed as well. (3) The research status, advantages and disadvantages of the measurement techniques in microwave band are introduced briefly. (4) The existing problems in the multi-angle scattering properties measurement techniques are summarized, and the corresponding research hot spots and development trend are prospected. This work can provide a reference for the further study of the multi-angle scattering properties of the atmospheric particles.

The total atmospheric transmittance is an important parameter reflecting the optical properties of the whole atmosphere, which is of great significance in the study of laser atmospheric propagation, infrared radiative transfer and the engineering application of photoelectric systems. The measurement principle of laser heterodyne technology is introduced firstly, especially the principle and method of high-resolution measurement of the total atmospheric transmittance by using laser heterodyne spectroscopy, as well as the method of simultaneous inversion of the profile distribution and column concentration of water vapor. Then the high-resolution laser heterodyne spectrometers at 4.5 μm and 3.53 mum band developed by our research group, with 0.006 cm-1 and 0.002 cm-1 spectral resolutions respectively, are introduced, and the typical measurement results of the total atmospheric transmittance, water vapor profile distribution and column concentration in Hefei area with the two devices are also presented. Finally, the future development of laser heterodyne technology in photo-electric systems engineering is prospected.

Atmospheric optical turbulence is one of the principal factors that has effects on laser beams propagation through the atmosphere. In consideration of the uncontrollability of the actual atmospheric trubulence, it is necessary to establish a stable and controllable simulation atmospheric turbulence in laboratory in order to carry out the study of laser atmospheric transmission effect. In addition, the real-time measurement of multiple parameters of atmospheric optical turbulence is also an important research in the field of atmospheric optics. A device was set up in laboratory for simulating atmospheric optical turbulence by using the forced convection of hot air, and then the real-time measurement technology of atmospheric turbulence parameters, such as atmospheric coherent length, atmospheric turbulence intensity and internal scale, was studied. Under the approximation of geometrical optics, the parameters of atmospheric optical turbulence were obtained by measuring the irradiance fluctuations and arrival-of-angle fluctuations of laser beams after propagation through simulated-turbulence, and then the uncertainty in measurement was given by analyzing the experimental data. Finally, the experimental data was compared with the measurement results of literature. It is shown that the atmospheric turbulence simulation device developed in this work can be used for the real-time measurement of atmospheric turbulence parameters and the study of laser propagation effect in the laboratory.