A novel system for on-line measurement of the distance from the melt pool to the lens in laser material processing is described. A spectrometer analyzes the broadband radiation that is produced at the laser-workpiece interaction zone and then focused by the effector optics in the direction of the laser source. From the influence of chromatic aberration on the detected radiation spectrum, the distance from the workpiece to the lens can be derived. An analytical calculation of the shift of the melt pool spectrum that depends on the distance between the molten zone and the focusing lens shows good agreement with the measured results.
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