Intensity and Time Resolved Scattered Laser Radiation Monitoring in Single Pulse Micro-Drilling as a Method for Quality Control

This paper presents a monitoring system for scattered laser radiation in the single pulse microdrilling process.Scattered laser radiation is non-absorbed radiation scattered both at the surface and in the particles of the material removed.The system developed to measure this radiation is based on a fiber optic bundle attached to a narrow filter photodiode that captures the scattered light symmetrically around the area where the micro-drilling is performed.This provides sensitivity to non-symmetrical scattering processes (for example, in the event that the sample is tilted) and enables the system to be simplified by using only two photodiodes: One to monitor the beam entrance area and the other to monitor the beam exit.Two types of analysis are carried out on the two sides of the sample: Intensity monitoring and time resolved monitoring.The former can be used as a detector of deviations in the configured micro-drilling process and the latter as a real measurement of drilling time.A further analysis of these measurements enables correlations to be established with process parameters and physical scattering processes.The system designed is a low-cost tool for real-time quality monitoring of large, time-consuming industrial micro-drilling processes.