Beacon Laser Aperture Launch And Receive Efficient Coupler

The technology of coupling and splitting beam in common aperture with high efficiency is studied for the need of research and application of laser guide star(LGS) in astronomy and directed-energy system, including polarizing beam coupling and splitting technology, rotating mirror beam coupling and splitting technology and frustrated total internal reflection(FTIR) beam coupling and splitting technology. These technology can improving the detecting ability and receiving efficiency of the LGS system, reduce the power request for the LGS laser, and cut down the cost of the system using adaptive optics(AO).The polarizing beam coupling and splitting technology for LGS is the main part of this study. During the rotating of the telescope the phase difference between s wave and p wave will change, and the receiving efficiency of the polarizing beam coupling and splitting system will decrease. The physical model of polarizing beam coupling and splitting system using altazimuth coude telescope is built up based on Mueller matrix and Stokes vector. The phenomena of the decreasing of the receiving efficiency are successfully explained by this model. Three dynamic phase compensation solutions are proposed: 1) Two quarter-wave plates are rotated to compensate the phase of the laser. 2) A Faraday rotator is fixed and only one quarter-wave plate is rotated. 3) A Faraday rotator is fixed and the phase retard of a Berek compensator is adjusted to compensate the phase of the laser. The validity and continuity of these three solutions is numerically simulated, and the results show that all of them can make the receiving efficiency be better than 90% after compensation. The phase compensation may be discontinuous in solution 1 and 2, but solution 3 has a continuous and stable compensation process.An experimental equipment of polarizing beam coupling and splitting is built up, and phase compensation experiments using solution 2 and solution 3 are separately done. In the first experiment, the rotating angle of the quarter-wave plate is calculated using information about the phase difference, azimuth angle and zenith angle of the telescope. The average receiving efficiency acquired in this experiment is better than 90%. In the second experiment, the receiving efficiency is measured by a light power meter and used as a feedback to control the phase retard of a Berek compensator. The polarizing beam coupling and spitting system is stable and the average receiving efficiency is larger than 90% after closed loop compensation. In order to get the rotating angle of the quarter-wave plate in solution 2, the phase difference caused by the plane mirror is accurately obtained by experiment.The technology of rotating mirror beam coupling and splitting is also studied. The structure and sequence of the rotating mirror is designed to enable the time gating for Raleigh LGS. The analyses based on geometric optics indicate that the vibration of the mirror will lead to a beam-excursion and a focal departure. The physic model of the rotating mirror beam splitter is built up and then the formula of the beam-excursion and focal departure caused by the vibration of the mirror is deduced. Grounded on this, the optical and structural design is optimized to reduce the beam-excursion and focal departure caused by the mirror.The principle of FITR and the working sequence of the FITR shutter is introduced. At last, the feasibility of using FITR device in the beam coupling and splitting system of LGS is analyzed.