Measurement of lens parameters based on Shack-Hartmann wavefront sensor

Abstract

The focal length, radius of curvature, and refractive index are key parameters of a spherical lens. Here, an approach for measuring lens parameters based on the Shack-Hartmann wavefront sensor (SHS) is proposed. Firstly, the position of the reference point for measuring focal length is determined by the figure-of-merit function, called the least square sum of centroids shifts (LSSCS), from the spot array formed by the microlens array of SHS. The focal length is estimated by measuring radii of curvatures of two spherical waves. Each spherical wave is caused by the distance between the focal point of the lens and the determined reference. Secondly, the radius of curvature is the difference between two coordinate locations of the lens. Each location, corresponding to a collimated beam reflected from the lens, is determined by the figure-of-merit function LSSCS. Thirdly, the refractive index can be further estimated by lens maker's equation through the measured focal length and radius of curvature. A positive and a negative lens are both tested by the proposed method. Experimental results show that the lens parameters measured by the proposed method are in good agreement with the nominal values. The proposed method does not require wavefront reconstruction, and is simple, accurate and noise-resistant.