System for the measurement of the deviation of a laser beam from the vertical direction

If a used "vertical beam" is not perfectly vertical in a measurement, a cosine error will be introduced into it. To decrease and compensate for this cosine error, a measurement system is proposed to measure the deviation of the laser beam from the vertical direction. The structure of our measurement system is illustrated, and a model for solving for the deviation angle is established. As the distance of the beam spots on the charge-coupled device is the essential parameter for the measurement results, the acquisition process for this distance is explained. Moreover, the accuracy of the algorithm used in the acquisition process is also tested by experiments. Further, a self-correction module is designed and applied to reduce the error caused by the corner cube reflector in the system. The characteristics of the measurement system such as the resolution, stability, temperature drift, and direction accuracy are analyzed through experiments. The combined uncertainty of the measurement system is calculated to be 11×10^-6  rad.