Optical earth imaging simulation of a space target in orbit and it's extraction in laser illumination condition were discussed. Based on the orbit and corresponding attitude of a satellite, its 3D imaging rendering was built. General simulation platform was researched, which was adaptive to variable 3D satellite models and relative position relationships between satellite and earth detector system. Unified parallel projection technology was proposed in this paper. Furthermore, we denoted that random optical distribution in laser-illuminated condition was a challenge for object discrimination. Great randomicity of laser active illuminating speckles was the primary factor. The conjunction effects of multi-frame accumulation process and some tracking methods such as Meanshift tracking, contour poid, and filter deconvolution were simulated. Comparison of results illustrates that the union of multi-frame accumulation and contour poid was recommendable for laser active illuminated images, which had capacities of high tracking precise and stability for multiple object attitudes.
In the field of laser applications, it needs to know the optical characters of sea’s atmosphere. By referring, measuring and theoretically studying, the optical characters of atmosphere of China’s sea are studied herein. These optical characters are mainly about C<sub>n</sub><sup>2</sup>, and visibility, and so on. And the differences between sea and earth are compared with their optical characters. Then, some basic and important conclusions are made.
Thermal blooming effect of inner optical path remarkably affects far-field beam quality and energy distributions which should be taken into account in high energy laser (HEL) system. A physical model of thermal blooming is established. Based on the model, numerical simulations are carried out to study both the influences of absorptions of laser energy and tube structures on laser propagation in a closed tube. The natural convection of gas is numerically simulated by computational fluid dynamics (CFD) method. Gas temperature distributions, additional phase differences (APDs), variations of beam quality and drifts of mass center in far-field under different absorptions of laser energy and tube structures (Z-shaped and U-shaped) are compared, respectively. By analysis of numerical simulation results, the switch time of heat conduction and heat convection in gas is distinguished, which significantly affects the variations of beam quality and drifts of mass center in far-field. In addition, it also indicates that less absorption of laser energy improves beam quality and delays the switch time of beam quality between two heat transfer mechanisms. Therefore, it is significant to control the absorptions of laser energy for HEL system in practice. Different tube structures owning different beam paths change the distributions of APDs and thus influence beam quality. APDs of the two horizontal sections are the same (superposition effect) for Z-shaped tube while inverse (compensation effect) for U-shaped tube. It is shown that drifts of mass center in far-field are greatly suppressed for U-shaped tube than that of Z-shaped tube and beam quality is also improved.
The image quality of space object or the Laser propagation characteristics in atmosphere will be degraded by the effect of turbulence. Adaptive optics can be used to correct atmospheric turbulent aberration, but the anisoplanatic effect of atmospheric turbulence is unavoidable. Adopting the special spectral filtering method, different type of anisoplanatism in different scene are systemically modelled, and the formulae that describing different type of anisoplanatic variance and their Zernike model components are obtained. According to HV turbulent outline, the characteristics of Zernike model components of different type of anisoplanatic variance are analyzed.
EasyLaser is component-based laser system simulation software. Beam control system simulation is a main part of EasyLaser, which can be used for systems with multi-optical paths, multi-wavelength beams, and multi-controllers. A new numerical method about general kinematics separation is proposed for beam control system simulation. It provides axis rotation conversion relationships due to orientation data of apparatus of system, such as gimal, sensor and optical mirror. It gives their coupling and uncoupling matrixes in kinematics and controller model. The matrixes could change every iterative time automatically during the dynamic tracking process. The main advantage of the method is more suitable to solve the problems that the gimbal movement and geometry optical transmission are considered simultaneously. By using the method, sensor images and undershoot data are updated automatically. And further the kinematic driver or controller signals are separated automatically. Therefore the tracking and beam control can be designed without consideration of the system kinematical composition. Then the beam control system simulation has the virtues of generality, flexibility, and usability. No matter what kinds of gimbal and optical path, designer needs only to consider tracking and beam control aspects. In addition, a union beam control example for atmosphere transmission correction is given. It includes tracking tilt mirror and adaptive optics system. Simulation results show that the low-frequency fluctuation is restrained effectively and the high-frequency fluctuation is corrected obviously.
Adaptive optics (AO) system can be used to detect and compensate the aberrational wavefront of beam in real time. The compensative ability will be affected by the detecting precision of wavefront. Noise is one of the most important factors that affect the detecting precision of Hartmann-Shack (HS) sensor. Noise can induce the errors of centroid detected by HS sensor, consequently influences the wavefront reconstruction. Based on the characteristic of Charge Coupled Devices (CCD), the model that simulates the detecting precision of wavefront affected by noise is built. Based on the factual application scene of artificial beacon, for typical HS sensor, the effects of noise on the detecting precision of wavefront are simulated, and the relations of wavefront beam spot in CCD, and the number of pixel used to calculate spot centroid are analyzed. Several results that can be used in engineering application are obtained.
The concept of asymmetrical thermal blooming (ATB) effect of intense laser beam propagation through atmosphere is presented. The numerical simulation results for simplified cases are given. Some analyses of the ATB effect have been done.
The beam spot will break up into some cracks when laser propagates through the turbulent atmosphere. The
characteristics of the cracked beam spot are studied statistically for different apertures and beam qualities, and with
different turbulent strengths. It is shown that, with the degeneration of the beam quality and the turbulence being
stronger, the total size of the beam spots and the numbers of the fragments will increase; meanwhile the scale of the
fragments will keep invariable almost. Four special situations are analyzed and the physical hypostasis of Fourier
transformation is discussed to understand these results.
On the base of the detailed numerical computations by 4-D wave optics code, the scaling laws for estimating the thermal blooming effects on target of the atmospheric propagation of high energy laser, for both horizontal and slant paths are given.