The elimination-compensation-utilization technique of the turbulence effects of the collimated laser beam in the atmospheric propagation--The distribution and compensation of the spot dance

when a laser beam passes through the turbulent atmosphere, the main effects which influence the displacement measurement or alignment are the intensity fluctuation, the intensity distribution (speckle), the spot dance and the spot expansion. The effects obey a certain statistical distribution and possess a certain width of probability density distribution curve (spetro-width in brief). And the precision of the displacement measurement or alignment depends upon the spetro-width. Based on the displacement-time converting technique (G.L. Tan J. Optics, Paris, 1981, vol. 12,4) the turbulent influence on the displacement measurement could be replaced by the effects which is of pulse amplitude, pulse shape and the fluctuation of the pulse appearing moment on the time axis. The influence of the photoelectric pulse amplitude and pulse shape on the displacement measurement may be eliminated. (G.L. TAN, ICL Digest, 1983, GUANGZHOU, CHINA). The rest, the fluctuation of the pulse appearing moment on a time axis is just the motion of spot dance of a laser beam passing through the atmosphere. We carried out the experiment to determine the distribution of spot dance, and compared the experimental distribution with that of the ideal distribution. The main conclusion is that the spot dance obeys a normal distribution either in the strong turbulence or in the weak turbulence, whether in the wind rising before or in the wind blowing with the drop in temperature. The maximum deviation of the experimental distribution related to the ideal normal distribution is of -5.5% in the weak turbulence, of 14.2% in the strong turbulence, of 8.4% in the wind rising before and of -18.5% in the degree wind of 4 with the drop in temperature. The probability density distribution curves are shown as in FIG.(1) and FIG.(2).