Power coupling of a two-Cassegrain-telescopes system in turbulent atmosphere in a slant path

The characteristics of dark hollow beams passing through a two-Cassegrain-telescopes system in turbulent atmosphere in a slant path have been investigated. The distribution of the average intensity at the receiver telescope and the efficiency of power coupling with respect to propagation distance with different parameters are derived and numerically calculated. These studies illuminate that the power of the dark hollow beams is concentrated on a narrow annular aperture at the source plane and its power coupling with a transmitter Cassegrain telescope can remain quite high. For short distance between the two Cassegrain telescopes, the normalized average intensity distribution at receiver plane holds shape similar to that at the source plane, and the two Cassegrain telescopes keep high efficiency of the power coupling. But with the increment in the propagation distance, the power of the dark hollow beams gradually converges to the central and the spot spreads. The central obscuration of the receiver telescope blocks more of the power; meanwhile more of the power moves out beyond the edge of the receiving aperture. Therefore, the efficiency of the power coupling decreases with the increment in the propagation distance. In addition, the relations between the efficiency of power coupling and wavelength of laser beams are also numerically calculated and discussed.