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In order to lead the laser beam transmit in the atmosphere convergently, an experiment of laser focus at the distance of
450m and 300m has been operated in the outdoor place. The actual manipulations are as follows: Firstly, the laser was
collimated by a beam expander, then the near-parallel laser beam was transmitted with a Galileo telescope system, and
the distance between the concave lens and the convex lens can be tuned through a precise displacement platform, so the
focus of the system changed due to the tiny displacement of the concave lens. Secondly, the average power of the laser
spot can be measured using power meter, the power is 47.67mW and the standard deviation is 0.67mW while the focal
length is 450m. Thirdly, the energy distribution was found through the laser beam analyzer. The spot images were saved
using the beam analyzer, then the saved image can be processed with Matlab software afterwards. The function named
EDGE and Sobel operator was used in the pre-processing of the saved image, then method of median filter was used in
the course of image de-noising and 53H filter was adopted in the signal analysis. The diameter of laser spot was obtained
by the method above, the diameter is 5.56mm and the standard deviation is 0.24mm. The spot center excursion is
0.56mm, it is 10.43% of the total diameter of the laser spot. At last, the key factors of the energy dissipation in the
focusing system can be summarized as follows: restriction of the diffraction limit, attenuation in the atmosphere,
geometrical aberration of optical system, and the diffraction limit and the geometrical aberration are significant in the
three factors above, so we can reduce the impact of the both factors during the design of optical system. The reliable
referenced data of the system design can be acquired through the primary experiment research.
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