High-precision laser alignment technique based on spiral phase plate

Abstract

The laser alignment technique is widely used in the measurement of straightness due to its unique capabilities of non-contact detection, fast response and high accuracy. By coupling the laser beam into a single-mode fiber, traditional alignment method can be greatly improved, since the emitting beam from the fiber basically won’t be affected by the variation of the incident intensity distribution. However, such method still suffers from errors caused by the vibration of the emitting fiber end and air turbulence. In this paper, the traditional alignment reference, which is the centroid of the intensity distribution, is replaced by center of the dark spot in a diffraction pattern, by adding a spiral phase plate (SPP) into the optical path. The center of the dark spot is proved to be stationary when the laser beam drifts. The far-field diffraction model of SPP is theoretically analyzed in detail. In the calibration experiments, the detected position data of the scanned CCD is highly linear with a correlation coefficient of 0.99999. The system is guaranteed with outstanding stability by a series of experiments, in which the standard deviation of the x and y coordinates are respectively only 7.0% and 33.7% in short-term tests and 20.3% and 25.3% in long-term tests. With simple configuration, the proposed system demonstrates satisfying performance in laser alignment.