Real Time Measurement of a Surface Displacement with Two Laser Beams

Abstract

An optical method for measuring surface displacement in real time has been proposed by means of a system composed of two laser beams, and is discussed analytically using paraxial optics. The normalized light intensity defined by both the lights, I=(I1-I2) / (I1+I2), was expressed by I =-2(f1-f0) 2 (1/q) ∆f0, where f1 and f2 are the focal lengths of the first (objective) and second (focusing) lenses, q a distance between the pinhole and the focal point of the second lens for both laser beams, and ∆f 0 surface displacement. The above analytical result has been roughly verified by preliminary experiment, though there were differences in absolute intensity between the experimental and the analytical results. The spatial resolution of this method was expected to be about 2 µm from these analytical and experimental results.

Interaction Between Line Soliton andY-Periodic Soliton: Solutions to the Asymmetric Nizhnik–Novikov–Veselov Equation

“…The first and main reason for this difference is the pinhole size, which was assumed to be infinitely small in the theoretical analysis but in practice was 0.2 mm. The second reason is that this theoretical value was obtained based on the paraxial optics as was shown in a previous paper [9]. The final reason is a slight shift of both optical axes on the pinholes A 1 and A 2 , which is another main reason for this difference.…”

“…In contrast to the reflection method described above, an imaging method [7], a laser interferometry method [3,4] and a two-laser light method [8,9] can all be successfully used for almost all the samples, since a rough surface can be examined by means of the scattered light on the surface. Figure 4 shows the basic optics of this method.…”

“…Some representative devices for the measurement of longitudinal resolution on a sub-nm scale have been developed, which are all based on laser interferometry employing sub-nanometre double shearing heterodyne interferometry [3] or a phase shift method [4]. Another device has been developed by the present authors, which is based on laser reflection [5]. Both methods [3,4] utilizing laser interferometry are based on the imaging of an irradiated area, and thus can obtain two-dimensional information instantaneously.…”

“…However, the data processing involved with these methods is relatively time consuming since analysis of the interferogram is moderately difficult. Also, these methods and devices [3][4][5] for nm measurement are very complicated and expensive. Our method, on the other hand, though it can scan only a line on a surface and requires many measurements to scan a two-dimensional region, is relatively simple and inexpensive, and provides a real-time technique for data acquisition.…”

A hybrid sensor for the measurement of a wide range of longitudinal surface displacement based on laser reflection and scattering

“…One of the representative devices currently in the market is manufactured by Keyence at Osaka in Japan and is based on the imaging method [7]. Another developed by the present authors is based on scattered light intensity [8,9]. Both methods employ a principle involving scattered light on a surface, but differ in practice.…”