Study On Laser Pointing System Using Return Photon Signal

Laser applications including active tracking and free-space laser communicationrequire high precise pointing control. However, when the laser beam is illuminating thetarget, the pointing errors due to the limitations of the tracking system, mechanicalvibration, atmosphere turbulence, and the optical misalignment, will cause pointingoff-axis and the energy loss on the target. Determining of these errors has historically adifficult problem-especially for a non-cooperative target, most of which are in a state ofopen-loop pointing. In order to explore a method of pointing errors estimation andclosed-loop pointing realization with the non-cooperative target, this paper studies thepointing technology using return photon signal.In this paper, the history of pointing technology using return photon signal isreviewed and the significance of this research is pointed out based on the applicationsand trends. Then, this novel pointing technology is introduced according to a fieldactive illumination experiment. A physical model of return photon signal is given.And the theory of pointing errors estimation is described.A numerical simulation system is established for the return photon signal withactive illuminating the target. The entire physical process of photons from the emissionto reception is simulated, which contains boresight and jitter, vacuum laser transmitting,atmospheric turbulence, reflecting process of target, scattering photons transmission,return photon signal processing, and closed-loop control simulation. Based on thesimulation system, the theory of pointing errors estimation is verified and theperformance of every estimation algorithm is analyzed according to sample size, jitterand boresight.In order to estimate the direction of boresight error, a triangular scan algorithm ispresented. And the Cramer-Rao lower bounds (CRLB) performance of the triangularscan algorithm is induced in closed-loop pointing applications. The simulation resultsdemonstrate that the closed-loop pointing using return photon signal can be realized bythe triangular scan algorithm, and the performance closes to the CRLB. The closed-looplaser pointing with the pointing errors estimation is realized by this method for the firsttime.A laboratory platform for the laser pointing system is set up. Then, a closed-loop pointing experiment is realized using two-dimensional hill-climbing algorithm based onthe return photon signal. And the anti-jamming capability of hill-climbing algorithm isanalyzed. What’s more, the experimental verification of maximum likelihood estimationis given. Mean while, a closed-loop targeting experiments by triangular scanningalgorithms is presented. And the performance of this method is analyzed from residualsaccuracy.A noise model of return photon signal is established. Then, in order to eliminate theenergy fluctuation of laser source, transmission distance changing and tracking zenithchanging, a normalization model of return photon signal is given. Secondly, in order tosolve the distribution changing of return photon signal when illuminating extendedtarget, an equivalent far field distribution parameter of laser beam is proposed. Thirdly,the impact of the speckle noise reflecting from diffuse target for the return photon signalmeasurement is described. A scheme for lessening the speckle noise is given andverified with simulations. All of the work done above laid a theoretical foundation forfield experiment.In order to study the performance of the pointing technology using return photonsignal in the atmospheric environment, a field experiment platform is set up, whichcontains: pulse laser launch system, return photon signal reception system based onrange gating, and a control system on Labview platform. Under the field environment,the performance of the pointing errors estimation and triangular scanning algorithm isverified. And a closed-loop pointing experiment is realized based on return photonsignal.Finally, for the problem of pointing technology using return photon signal inengineering applications, two novel designs are proposed. These solutions laid thefoundation for the engineering realization of this pointing technology.