The primary structure design of a birefringent lens with the concept of pseudo-chromatic aberration

Much attention has been paid to the optical design of a birefringent lens and analysis of its polarization aberration due to its essential application in bifocal interferometric microscopes. To investigate a practical way of designing a birefringent lens with large separation between the two foci, a novel concept named 'pseudo-chromatic aberration' is proposed, which results from the difference of refractive indices between the ordinary and extraordinary rays when they pass through the birefringent lens. As the concept is similar to normal chromatic aberration, the existing primary aberration theory to design a thin cemented lens can also be adopted on the design of a birefringent lens. A table of primary structure of cemented doublet birefringent lenses is consequently obtained. Different combinations of three kinds of birefringent crystals and optical glasses can satisfy various requirements. A concrete example of a birefringent lens with the compactness factor γ of 0.25 is given using the glass of SF2 and calcite.