Ultrafast lasers have proven to be an effective tool to improve the process quality when machining hard ceramic materials such as silicon carbide, silicon nitride and alumina, as well as hardened alloys. We have developed an in-line optical displacement sensor that is coaxial with the laser processing beam and measures the part surface height at high-speed (80 kHz) with sub-micron axial resolution and a measurement range of >3 mm. The sensor was integrated into a laser micromachining system with a 40W ultrafast IR laser (1030 nm, 400 mJ, 190 fs), a 5-axis motion system, and a custom scanhead that creates a common optical path for the process and sensing beams. In this configuration, the sensor can record the local surface height of a part across the optical field to generate a 2-D profile of the surface, which is used to generate a point-cloud for further analysis. A calibration standard and process has been developed to ensure the measure surface profiles are accurate in 3-D (XY and Z).

The micromachining system was tested on ceramic (SiC, SiN, Alumina) and titanium alloy (Ti-6Al-4V) samples by machining various features and scanning them with our in-line profiler. The results of the scanned features were validated with measurements from a confocal scanning laser microscope.