Noncontact profiling of machined metal surfaces by fiber optic interferometry

A rugged interferometric fiber optic instrument for non-contact profiling of optically rough, machined metal surfaces has been developed, designed for use on the machine tool. The sensor is a robust and compact interferometric probe which scans focused light across the test surface. A laser diode source and photodetector communicate with the sensor through an optical fiber, and the output is demodulated with a phase-stepping algorithm, achieved by frequency modulating the source. Operation is demonstrated with face-milled steel surfaces, with steep local gradients and local variations in reflectivity of a factor of 100,000. The measured horizontal resolution is 1.5 µm, and the noise-limited vertical resolution 0.3 nm/vHz. Two additional manufacturing applications are demonstrated: in-situ profiling of diamond-machined surfaces and score dies.