到达角起伏谱测量的影响因素

考虑了接收孔径滤波作用和实际湍流场速度起伏对到达角起伏谱测量的影响，理论分析得到了均匀光路情况下到达角起伏谱的表达式。计算结果表明，当接收孔径较小时，到达角起伏谱的高频端和低频端形状都有较大的衰减，而接收孔径大时，到达角起伏谱的高频端和低频端衰减较小；当速度起伏小时，到达角起伏谱高频端衰减快，反之，当速度起伏不大时，到达角起伏谱高频端衰减慢。利用湍流池模拟实验，让准直激光束通过湍流池，当改变接收孔径的大小时，测量到到达角起伏谱的变化；实验中，准直激光束的直径为0．1m，选取的接收孔径直径分别为0．1m，0．03m和0．01m，实验数据较好地验证了接收孔径大小对到达角起伏谱测量影响的理论结果。

Factors Affecting Spectral Measurement Arrival-angle Fluctuation

An expression of arrival_angle fluctuation spectrum for the collimated light propagating through homogeneous turbulent media is developed, when the effects of filter of lens and the real fluctuation of velocity on measuring the spectrum of the arrival_angle fluctuation is taken into account. The calculating results are that: high_frequency and low_frequency end of arrival_angle fluctuation spectrum will decay fast when the aperture of lens is small, but they will decay slowly when the aperture is large; and when fluctuation of velocity is minor, high_frequency end of arrival_angle fluctuation spectrum becomes steeper, while on the contrary, when fluctuation of velocity is strong, high_frequency end of arrival_angle fluctuation spectrum becomes flatter, which is due to the smoothing effect of fluctuation of velocity on arrival_angle fluctuation spectrum. On the current experimental conditions, the theoretical results are confirmed. The experiments are finished in a laboratory turbulence cell. The collimated laser beam with the diameter of 0.1 m passes through the turbulence cell where the diameters of the receiving aperture are 0.1 m, 0.03 m and 0.01 m respectively. The spectrum of the arrival_angle fluctuation will change spontaneously. Data from laboratory simulation of the turbulent cell are in agreement with the theory about small apertures.