レーザ光 (6328Å) の大気伝播による偏光変動の測定について(第 1 報)
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概要
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It is known that, on propagation of the laser light beam (6328A) through the atmosphere, various kinds of random variations such as the random attenuation of beam power, deformation of beam pattern, beam spot dancing, phase fluctuation are observed and their researches have been reported by many authors. Among these phenomena, our effort is directed towards determination of the method of precise measurements to find the variation of polarization characteristics caused by the refractive index fluctuation of the atmosphere, to show the value of polarization fluctuation and the statistical relation between meteorological conditions and observed phenomena. Though the experiments reported here are performed under relatively short propagation path over total path of 142meters (one way of 71meters) folded by a reflection mirror and with the mean height of 10meters above ground, the beam power fluctuation exceeds noise level from the light beam oscillator and the polarization fluctuation is of the order of 10^<-2>∿10^<-1>. In the case where the plane of polarization is rotated by modulation, in communication applications, such fluctuation seems to degrade signal to noise ratio. To estimate the degree of polarization degradation, the plane of polarization in the beam is directed towards 45degree measured from the vertical plane and the difference of vertical and horizontal components of the polarized field is obtained by differential amplifier and recorded automatically after the field is separated into these components. Atmospheric transmission experiments and tentative simple experiments show that this polarization fluctuation is mainly due to the effect of refractive index fluctuation caused by temperature variations of the air.
- 1971-03-31