The design of infrared double-layer refractive–diffractive inverted telephoto optical system

In this paper, the double-layer harmonic diffractive element (HDE) structure is investigated and the optimization procedure is given based on the equation of diffraction efficiency of the double-layer diffractive optical element. A new infrared double-layer inverted telephoto with HDE is designed, which can work in the mid- and far-infrared wavebands. The diffraction efficiency of the system at each wavelength in the designed two wavebands is larger than 90%, which improves the image contrast and the imaging quality significantly.