A method to diverge reflected beam uniformly using cube-corner retroreflector array with dihedral angle tolerances

Abstract

The cube-corner retroreflector (CCR) is widely applied in the electro-optical tracking, satellite communication, interferometers and adjust-free solid state laser. In some applications, the incident beam emitted by a laser is reflected back by the CCR to a photoelectric detector. The distance between the photoelectric detector and the laser source on the ground is much larger than the diffraction-limited spot. Meanwhile, the attitude angle of the CCR would randomly vary for the jitter of the platform. Therefore, the reflected beam should be diverged uniformly at far-field, whereas the normal CCR cannot achieve the divergence on the reflected beam. The investigation indicated that six sub-spots are generated by a CCR with dihedral angle tolerances at far-field. According the characteristics of the CCR with dihedral angle tolerances, a structure and its design method are proposed to diverge the reflected beam with a CCR array. The azimuthal angles of the every CCR of the array should be specially designed to generate an annular and uniform pattern. Due to the propagation distance is much larger than the size of the CCR array, the feasibility of the method is analyzed by the wave theory. A CCR array with a divergence half-angle of 0.5 mrad is designed, in which the dihedral angle tolerance of every CCR is 20. The influences of the beam and structure parameters on the diffraction characteristics of the reflected beam are investigated. The numerical results indicate the divergence half-angle of the CCR array varies quasi-linearly with the change of the dihedral angle tolerance, and the intensity distribution of the incident beam does not influence the divergence half-angle. The propagation distance does not affect the uniformity of the reflected beam when the CCR array satisfies the point source condition. When the number of the array element increases to a certain value, the increase of the number can strengthen the intensity and hardly influences the uniformity of the reflected beam. For the restriction of the machining and assembling technics, the dihedral angle tolerance of every CCR is hardly identical and the assembling azimuthal angles of the array element can not be identical with the design result. Therefore, the influence of the assemblage azimuth error and machining accuracy of the dihedral angle are studied. It reveals that the assemblage azimuth error does not remarkably the reflection pattern, whereas the machining accuracy can observably affect the uniformity of the reflection pattern, which can be resolved by the growth of the number of array element.