Measurement of the refractive index and thickness for lens by confocal technique

A new confocal measurement for lens refractive index and thickness is proposed based on the property that the peak of an axial intensity curve precisely corresponds to the focus of the objective in a confocal system, which uses the peak of confocal axial response curve to precisely identify the positions of the objective when the measurement pencil is focused on the vertex of the test lens and the reflector with or without the test lens in the measurement light-path, and then uses ray tracing facet iterative calculation to obtain the refractive index and thickness of the test lens simultaneously. The preliminary experiments indicate that the measurement accuracy can reach about 3.8 × 10^-4 for the refractive index and 0.05% for the thickness.