Optically anisotropic crystalline grisms for astronomical spectrographs

Abstract

We show that a crystalline LiNbO₃ grism and a hybrid grism made of a LiNbO₃ transmission grating and a ZnS prism can be new and powerful dispersing elements with refractive indices high enough to realize high spectral resolution for visible to near-infrared astronomical spectrographs with transmission optics. We describe the basic principle and the limitation to minimizing the spectral separation that is due to the inherent birefringence of such an optically anisotropic crystal used for grisms.