Investigation of the refractive index distribution in precision compression glass molding by use of 3D tomography

Compression molding of glass optical components is a high volume near net-shape precision fabrication method. In the compression molding process, refractive index variation is often introduced in glass during cooling. The variation of the refractive index in a molded glass lens is an important parameter that can influence its optical performance, especially for lenses used in high precision optical systems. In this research, the three-dimensional (3D) refractive index distribution in molded glass lenses was studied using an optical setup based on the Mach-Zehnder interferometer and filtered back-projection reconstruction algorithm. Specifically, phase information was first evaluated by measuring interferometric fringes using a digital camera at pre-determined discrete locations. The 3D refractive index distribution inside the molded glass lens was then calculated from the phase information.