In order to improve the capacity of beam collimation for laser beam expander, it is necessary to design a more reasonable
and feasible structure of beam expander system. Laser beam expander is used to compress the laser divergence angle, in
order to reduce the energy losing in long distance scanning acquisition system. This paper introduces the working
principle and design idea of the laser beam expander, the collimating multiplying power focal length and the collimated
magnification formula of expander main, secondary mirror. According to the third-order aberration theory, Considering
the spherical aberration, sine difference and divergence angle, the reasonable analysis of optical path, ZEMAX optical
design software was used to design large-diameter laser beam expander and analysis and optimize, And given the actual
design data and results. Display the maximum optical path difference is ±0.01λ of the main light ray and each light ray.
To combination the rear- group objective lens of Galileo and Kepler beam expander, a large-diameter(1.475m) laser
beam expander was designed with 0.2m in the diameter, 1/2m in the relative caliber. In the objective lens System, a
high-order aspherical was used to the aberration of extra-axial point. we can see that the image quality is close to the
diffraction limit from the curves of wavefront. In addition to improve image quality effectively, the system has the
characteristics of simple structure, less costly and less design difficulty to compare with the other beam expanding
system. And make the output beam's divergence angle smaller, energy density higher, and the beam quality has been
greatly improved. The results show that the beam expander is fully meet the design requirements, the use effect is good.
Design and research of laser beam expanding system not only improves the quality of the laser beam in the laser system,
but also enlarge the application field of laser technology in photoelectric system.