Chromatic modulation based acoustic analysis technique for in-process monitoring of laser materials processing

The analysis of acoustic waves produced during laser materials processing is widely carried out for characterizing, monitoring, and controlling the process. Traditional methods used in analyzing the acoustic data such as rms signal strength and variation analysis, frequency spectrum analysis are based on signal intensity modulation which offers the advantage of inherent simplicity. However, these basic intensity monitoring systems tend to be sensitive to spurious changes in intensity resulting from variations in the various electrical components within the system and the noise of the industrial environment. In addition, it is known that the acoustic intensity is dependent on the distance and observation angle between its source and acoustic sensor. In this article, a type of acoustic analyzing method based on chromatic modulation is presented. Chromatic modulation offers not only much more acoustic information, precise distinction of the ambiguous signals, and robust monitoring in the laser processing system, but it could also make control of the laser process easier by simple chromatic output factors. It is also shown in this article how a chromatic modulation technique may be utilized as an acoustic analysis method to monitor the laser cleaning process. Consequently, it was found that the chromatic acoustic analysis method could be successfully applied for surface monitoring in the laser cleaning process and could provide correct monitoring information in spite of sensor stand-off variation.