Online laser beam monitoring by detection of scattered light from dielectric mirrors

摘要

An online laser beam monitoring system is presented in this article that detects the power distribution of the observed beam from the scattered light on dielectric deflecting mirrors. It is a simple possibility for determining the laser beam intensity profile during a laser treatment. The laser beam remains uninfluenced during the measurement. This technique provides high-resolution online information about a laser beam's power distribution and beam size. It is capable of monitoring cw or pulsed laser beams at different wavelengths. This measurement instrument can also be used for adjustment, beam localisation and for detecting power fluctuations in real time. Two different types of near infrared lasers were used to test the method: a semiconductor laser (λ = 808 nm) and a Nd:YAG laser (λ = 1064 nm). Several microscopic techniques, atomic force microscope (AFM) and white light interferometer (WLI), were used to measure the topography of the mirror surface. This information about the surface roughness is used for predicting information about the expected scattered light. A comparison with a reference system highlights the quality and the applications of this measurement technique.