Far-field focal spot measurement based on DMD

Based on digital micro-mirror device(DMD), a novel method for measuring high power laser far-field focal spot with high dynamic range was proposed. The region of focal spot was divided into two segments with different intensity range through DMD, and then captured by two CCD respectively. Image fusion technique was used to put two results together and the intensity distribution of high dynamic range focal spot was acquired. Based on the digital control of DMD, focal spot with different forms can be measured efficiently. The principle of focal spot division using DMD and the approach to obtain DMD control signal template were analyzed and the procedures of image calibration and registration for focal spot reconstruction were explained. The feasibility of the new method was verified by experiment. The results show that a dynamic range of 3 000:1 is achieved through the proposed method.