High precision optical surface sensor

Abstract

A noncontact optical surface sensor with <1-nm resolution has been developed. The principle of this high precision optical surface sensor (HIPOSS) is based on the focus detection technique which has been employed in the pickup for optical disks. For focus detection, we chose the critical angle method of total reflection which used the steep reflectivity change around the critical angle. The HIPOSS was designed to increase the sensitivity and to eliminate some errors for nanometer order profilometer use. The size of the HIPOSS optical head is as small as 45 × 30 × 65 mm, so it can be installed side by side with a diamond stylus in the profile measuring instrument. These styli, if we term the HIPOSS an optical stylus, can be interchanged easily to obtain profile data on the same surface by different means, contact and noncontact. The repeatability of going and returning measurements is <1-nm rms, and the difference between HIPOSS and stylus measurements is also below 1-nm rms for most example surfaces. Using the high speed response of the HIPOSS, 3-D profile measurement over the workpiece and in-process measurements for ultraprecise diamond turning are also demonstrated.