**5.2.2 Collimated wave system**

This system has two sets of two-beam illuminations. One set, that is, an optical setup for displacement measurement using two-beam illuminations is shown in Figure 21. A collimated light beam from a laser is divided into an object wave and a reference wave by beam splitter 1. Additionally, the object wave is divided into object wave 1 and object wave 2 by beam splitter 2. Each object wave has a shutter on the light path. From the two holograms, the *x*-directional in-plane and the *z*-directional out-of-plane displacements are analyzed. Another set of two-beam illuminations provides the *y*-directional in-plane displacement.

Fig. 21. Optical using two beam illuminations

Fig. 22. Phase-difference displacement and strain distributions measured by collimated beam system

An L-shaped cantilever with a fixed line is measured by the system shown in Figure 21. Figures 22(a) and (b) show the phase-difference distributions along the *x*- and *z*-directions, respectively, obtained by the *x*-directional set. Figures 22(c) and (d) show the phasedifference distributions along the *y*- and *z*-directions, respectively, obtained by the *y*directional set. Figures 22(e) and (f) show the *x*- and *y*-directional displacement distributions, respectively. Figures 22(g) and (h) show the *x*- and *y*- directional strain distributions, respectively.
