Optical design of Offner-Chrisp imaging spectrometer with freeform surfaces

The Offner-Chrisp spectrometer is the preferred optical configuration in many spectroscopic imaging applications because it has several advantages over other similar instruments. Freeform surfaces enable imaginative optics by providing abundant degrees of freedom for an optical designer as compared to spherical surfaces, and offer many advantages in imaging application. An Offner-Chrisp imaging spectrometer with freeform surfaces is designed in this paper. The imaging spectrometer works at the wavelength range from 200 to 1500nm. The freeform surfaces are used to reduce the residual aberration over the large wavelength range and achieve a large flat field simultaneously. Different types of freeform surfaces are considered to evaluate their potential, e.g. anamorphic aspherical surface, X-Y polynomial surface and Zernike polynomial surface. Benefits from the freeform surfaces, the residual aberrations are well corrected, especially in the UV region and a flat field over the wide wavelength range is also obtained. The image quality is near diffraction limits. The smile and keystone are also well controlled <0.1 mu m.