Microlenses focal length measurement using Z-scan and parallel moiré deflectometry

In this paper, a simple and accurate method based on Z-scan and parallel moire deflectometry for measuring the focal length of microlenses is reported. A laser beam is focused by one lens and is re-collimated by another lens, and then strikes a parallel moire deflectometer. In the presence of a microlens near the focal point of the first lens, the radius of curvature of the beam is changed; the parallel moire fringes are formed only due to the beam divergence or convergence. The focal length of the microlens is obtained from the moire fringe period graph without the need to know the position of the principal planes. This method is simple, more reliable, and completely automated. The implementation of the method is straightforward. Since a focused laser beam and Z-scan in free space are used, it can be employed for determining small focal lengths of small size microlenses without serious limitation on their size.