GS(2)-11(GSW0444) A New Method of Measuring Aspherical Optical Surface

Abstract

Aspherical mirrors are being widely used in modern photoelectron instrument. Hence measurement of optical aspherical surface is necessary. At present, there are several methods to obtain the shape of an aspherical surfaces, such as phase shifting interference method, laser scanning method, three-coordination measurement method, etc. Phase shifting technique has many advantages but it is marred by a few inaccuracies due to the vibration and mechanical movement of the phase shifter itself. This paper presents a novel aspherical surface measurement technique based on the fringe projection. Sinusoidal fringes produced by a Michelson interferometer are captured by a camera and stored in a computer. The fringe patterns are project onto aspherical surface by a Liquid Crystal Display (LCD) Projection system, which takes the role of a piezo-electric transducer (PZT) phase shifter. The projected fringe patterns are captured by a CCD camera and stored in a digital frame buffer for subsequent analysis by a computer. In this system, phase shift is done electronically and thus errors due to the vibration and mechanical movement of the phase shifter itself and eliminated. The shifting operation is easy and rapid, and furthermore, the displacement can be done precisely. In contrast to the conventional phase shift method, this method is relatively simple and accurate, and is capable of conducting fully automatic measurement. A practical example confirms the predictions of the proposed method.