Full-aperture tilt measurement technique with a laser guide star

摘要

Abstract: A technique for measuring a full aperture tilt (FAT) with a laser guide star (LGS) is proposed. It is shown that information about a FAT is lost in a conventional LGS scheme because of the reciprocity of propagation paths. As a consequence neither the conventional LGS scheme nor its modifications with the receiver coaxial with the transmitter can be used to sense the FAT. A bistatic scheme that permits us to overcome the above difficulty is considered. This scheme permits us to single out the tilt component corresponding to the transmitting beam which is highly correlated with the FAT for a natural star. The tilt component corresponding to the reflected wave can be averaged out by averaging a LGS image motion over its angular extent. Such an averaging, however, does not affect the tilt component corresponding to the transmitting beam. This tilt conservation effect occurs due to the fact that a random motion of the transmitting beam causes a displacement of the LGS as a whole. The accuracy of measuring a FAT with a LGS is determined and the requirements for the measurement scheme are discussed.!28