Angle measurement method based on axicon lens

A method for measuring the incident angle of the light beam based on an axicon lens which defined by cone length and cone angle is presented in this letter. The system is mainly composed of a stop, an axicon lens, a telescopic system, an image receiving device, a display device and a digital image processing device. The light beam is refracted to a larger incident angle when passing through the telescopic system. It then goes through the aperture and the axicon lens, whose refraction times in axicon lens correlate with the incident angle, resulting in different spots captured by image sensor. The angle can be figured out with rich image characteristic information, which includes symmetry axis direction, area, the mass position center, the inertia moment, etc. In a practical design example, the image processing of the spot image shows that the rotational inertia of the spot has a one-to-one correspondence with the incident angle of the light beam, which features an obvious monotonicity. The angle measurement range can reach up to 3°, with an accuracy up to 1×10-3 ". Compared with the traditional angle measurement method, the measurement accuracy of this method based on axicon lens is improved by an order of magnitude. The system has the advantages of high accuracy, compact but simple structure, and no cumbersome installation and debugging. It can be used not only as a high-precision collimator, but also as a high-precision goniometer.