Glass material identification. (a) Geometric ray-trace model of RCM measurements showing the illumination cone focused on the front surface (blue), followed by the back surface (green) of the first lens element after the lens is translated axially by an offset (zc). zc is the confocal thickness and differs from the glass element thickness (zg) due to refraction of the marginal rays of the illumination cone. The red line represents the front surface normal at its intersection with the marginal ray. (b) Representative on-axis RCM axial response measured at 3 surfaces of an achromatic doublet (AC127-025-A, Thorlabs, Inc., USA). (c) Corresponding computational ray-trace simulating RCM illumination. (d,e) Log-error plots corresponding to the glass elements in (a). The insets show magnified cluster of glass materials near the minima. Red labels show manufacturer specified glass material for each lens element in (a). (f) Phase index (np) and Abbe number (vd) plot showing the relationship between identified and manufacturer specified glass material properties (dotted lines) for all 12 elements from Table 1. (g) Deviations in np and vd of identified glass materials relative to manufacturer specifications. Estimated 1 and 2 indicate materials that were characterized through air and an upstream element, respectively.