<title>Development of an optical probe for profile inspection of mirror surfaces</title>

Abstract

An optical probe for profile inspections of mirror surfaces is developed. This probe can detect the displacement and angle at one point on the measured surface simultaneously. Both the displacement meter and the angle meter of the probe use position sensing detectors (PSD) to detect the position of the optical spot. The principle of the displacement meter is the image formation system, and that of the angle meter is the autocollimation. The displacement meter and the angle meter have two important characteristics. One is the good linearity, the other is that they can detect the displacement and angle independently without interfering with each other. An optical fiber output is used as the light source so that the probe is made compact and to have good characteristics. To eliminate influences of disturbance lights, the light intensity of the laser diode is modulated by a sine wave of 20 kHz, only the position signal is taken out from signals obtained from the PSD in the demodulation circuit. According to the geometrical relation and the active size of the PSD, the displacement meter can measure more than 1000 micrometers and 120 minutes (arc) with good linearity, respectively. Estimating from the signal to noise ratio of the system, the displacement resolution and the angle resolution are 10 nm and 0.1 arcsec, respectively. Some experimental results to confirm the performance of the proposed probe are shown in this paper.