11.2 - A new method of contour measurement by gas lasers

A profiling apparatus, in which a He-Ne 6328-Å laser beam is used as a probe, will be described. The laser beam is focused on a target by a servo-driven optical system. An objective lens works not only for converging the laser beam but also for condensing the light scattered from the target. The displacement from focus was detected by a photodetector and a vibrating pinhole plate. Contour measurements were made on the surfaces of plaster, clay, and brass. The reproducibility in indicated distances was within 2 microns when the surface was stopped and the angle of incidence at the surface was nearly zero. As for the profiling of curved surfaces, the profiling errors from the plaster seemed to be lower than 40 microns. The errors from the rough surface of brass were 50 to 80 microns, but the highly glossy surface of brass created larger errors which were illustrated by a spherical aberration of the lenses.