Optical design of speckle suppression in laser measurement system

Abstract

Laser measurement system has the advantages of fast speed, high precision, and cost-effective. But the laser itself coherently produces speckles, the presence of laser speckle can seriously degrade image quality, leading to decrease in image recognition accuracy, thus reducing the accuracy of measurement. In this paper, we propose a multi-beam superposition method to reduce laser speckle. We use four lasers with equal optical power as the incident light source, then build the entire system light path by beam shaping and polarized beams superimposing, which achieves the line structured light required for the laser measurement system. According to the theoretical analysis and simulation optimization, the speckle contrast was reduced to 50% of the original value in this way. After beam shaping, we can obtain the linear laser beam with a line width of less than 1mm, a field of view angle of 66.8°, a light energy loss of less than 10% and an energy uniformity of 97.25% at a projection distance of 1000mm.The above results highlight a viable approach to decrease speckle contrast and measurement errors. This system can achieve high power and low speckle contrast light sources in the field of measurement, with outstanding result in practicability and convenience. On the other hand, this system can effectively solve the problems of serious error and low efficiency in measurement.