New optical system for reducing the interference fringe density in laser interferometric measurement of tooth flank form of a gear

In interferometric measurement, it is important to obtain a clear interference fringe pattern. A high density of fringes in interferometric measurements of involute gear tooth induces noises in the measuring signal and makes analysis difficult. In this paper, we propose a new optical system to obtain an interference fringe pattern of low density. A spherical concave lens is added in the optical path of the reference beam to deform the curved figure of phase of the reference beam over a charge-coupled device image sensor. By selecting a suitable focal length of the inserted concave lens, the phase difference between the reference beam and the object beam becomes fairly small over the CCD image sensor and the fringe density of the interference fringe pattern decreases. The effect of this new optical system is investigated.